ORCID Profile
0000-0001-5522-8887
Current Organisation
University of Southern Queensland
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Astronomical and Space Sciences | Stellar Astronomy and Planetary Systems | Astronomical and Space Instrumentation | Astrobiology | Astronomy And Astrophysics |
Expanding Knowledge in the Physical Sciences | Computer software and services not elsewhere classified | Physical sciences | Scientific instrumentation
Publisher: Oxford University Press (OUP)
Date: 12-08-2016
Publisher: Oxford University Press (OUP)
Date: 18-12-2020
Abstract: Studying cool star magnetic activity gives an important insight into the stellar dynamo and its relationship with stellar properties, as well as allowing us to place the Sun’s magnetism in the context of other stars. Only 61 Cyg A (K5V) and τ Boo (F8V) are currently known to have magnetic cycles like the Sun’s, where the large-scale magnetic field polarity reverses in phase with the star’s chromospheric activity cycles. τ Boo has a rapid ∼240 d magnetic cycle, and it is not yet clear whether this is related to the star’s thin convection zone or if the dynamo is accelerated by interactions between τ Boo and its hot Jupiter. To shed light on this, we studied the magnetic activity of HD 75332 (F7V) which has similar physical properties to τ Boo and does not appear to host a hot Jupiter. We characterized its long-term chromospheric activity variability over 53 yr and used Zeeman Doppler Imaging to reconstruct the large-scale surface magnetic field for 12 epochs between 2007 and 2019. Although we observe only one reversal of the large-scale magnetic dipole, our results suggest that HD 75332 has a rapid ∼1.06 yr solar-like magnetic cycle where the magnetic field evolves in phase with its chromospheric activity. If a solar-like cycle is present, reversals of the large-scale radial field polarity are expected to occur at around activity cycle maxima. This would be similar to the rapid magnetic cycle observed for τ Boo, suggesting that rapid magnetic cycles may be intrinsic to late-F stars and related to their shallow convection zones.
Publisher: Zenodo
Date: 2016
DOI: 10.5281/ZENODO.58288
Publisher: Oxford University Press (OUP)
Date: 04-2011
Publisher: Oxford University Press (OUP)
Date: 08-07-2020
Abstract: Asteroids and comets (planetesimals) are created in gas- and dust-rich protoplanetary discs. The presence of these planetesimals around main-sequence stars is usually inferred from the detection of excess continuum emission at infrared wavelengths from dust grains produced by destructive processes within these discs. Modelling of the disc structure and dust grain properties for those discs is often hindered by the absence of any meaningful constraint on the location and spatial extent of the disc. Multi-wavelength, spatially resolved imaging is thus invaluable in refining the interpretation of these systems. Observations of HD 48682 at far-infrared (Spitzer, Herschel) and sub-millimetre (JCMT, SMA) wavelengths indicated the presence of an extended, cold debris disc with a blackbody temperature of 57.9 ± 0.7 K. Here, we combined these data to perform a comprehensive study of the disc architecture and its implications for the dust grain properties. The deconvolved images revealed a cold debris belt, verified by combining a 3D radiative transfer dust continuum model with image analysis to replicate the structure using a single, axisymmetric annulus. A Markov chain Monte Carlo analysis calculated the maximum likelihood of HD48682’s disc radius ($R_{\\rm disc} = 89^{+17}_{-20}~$ au), fractional width ($\\Delta R_{\\rm disc} = 0.41^{+0.27}_{-0.20}$), position angle ($\\theta = 66{_{.}^{\\circ}} 3^{+4.5}_{-4.9}$), and inclination ($\\phi = 112{_{.}^{\\circ}} 5^{+4.2}_{-4.2}$). HD 48682 has been revealed to host a collisionally active, broad disc whose emission is dominated by small dust grains, smin ∼ 0.6 μm, and a size distribution exponent of 3.60 ± 0.02.
Publisher: American Astronomical Society
Date: 2022
Abstract: We simulate possible stellar coronal mass ejection (CME) scenarios over the magnetic cycle of ϵ Eridani (18 Eridani HD 22049). We use three separate epochs from 2008, 2011, and 2013, and estimate the radio emission frequencies associated with these events. These stellar eruptions have proven to be elusive, although a promising approach to detect and characterize these phenomena are low-frequency radio observations of potential type II bursts as CME-induced shocks propagate through the stellar corona. Stellar type II radio bursts are expected to emit below 450 MHz, similarly to their solar counterparts. We show that the length of time these events remain above the ionospheric cutoff is not necessarily dependent on the stellar magnetic cycle, but more on the eruption location relative to the stellar magnetic field. We find that these type II bursts would remain within the frequency range of LOFAR for a maximum of 20–30 minutes post-eruption for the polar CMEs (50 minutes for second harmonics). We find evidence of slower equatorial CMEs, which result in slightly longer observable windows for the 2008 and 2013 simulations. Stellar magnetic geometry and strength have a significant effect on the detectability of these events. We place the CMEs in the context of the stellar mass-loss rate (27–48× solar mass-loss rate), showing that they can amount to 3%–50% of the stellar wind mass-loss rate for ϵ Eridani. Continuous monitoring of likely stellar CME candidates with low-frequency radio telescopes will be required to detect these transient events.
Publisher: Oxford University Press (OUP)
Date: 08-2005
Publisher: EDP Sciences
Date: 2005
Publisher: Oxford University Press (OUP)
Date: 13-11-2021
Abstract: Mapping the large-scale magnetic field in late F-type stars is important for understanding the nature of the stellar dynamo and the dynamics of thin outer convection zones. We use Zeeman Doppler Imaging to produce multi-epoch maps of the surface magnetic field for two mature late F-type stars: β Virginis (F9V) and θ Draconis (F8IV). We also provide a magnetohydrodynamic model for the stellar winds from the corona to the inner astrosphere, which exists in an environment at the hot end of habitability for exoplanets. Our results show that either simple or complex dynamo magnetic fields are present in mature late F-type stars, with shallow outer convection zones. The results of stellar wind modelling show the average space weather for β Vir at a distance of 1 au falls within the range of space weather conditions observed at Earth, while θ Dra produces a wind pressure an order of magnitude stronger than the Sun’s wind pressure.
Publisher: AIP
Date: 2009
DOI: 10.1063/1.3246437
Publisher: EDP Sciences
Date: 04-2012
Publisher: Oxford University Press (OUP)
Date: 17-09-2014
Publisher: Oxford University Press (OUP)
Date: 04-2011
Publisher: Oxford University Press (OUP)
Date: 24-04-2020
Abstract: We present a spectropolarimetric magnetic snapshot survey of 55 stars which includes 53 F-type stars ranging from spectral types F0 to F9 plus 2 chemically peculiar stars β CrB, and δ Cap. We look for magnetic fields in stars spanning a range of effective temperatures where the transition from fossil to dynamo magnetic fields is believed to occur. High-resolution spectropolarimetry using circularly polarized spectra is used to look for a magnetic detection in the Stokes V profile, determine the mean longitudinal magnetic field (Bl), and to look for correlations with stellar parameters. Surface magnetic fields are detected on 14 F-stars, and present in every spectral class from F3V-F9V ranging in strength from 0.3 ± 0.1 G (36 UMa, F8V) to 8.3 ± 0.9 G (h Dra, F8V). Thus we find photospheric magnetic fields are present in stars as early as spectral type F3V with an outer convection zone thickness less than a few per cent of the stellar radius.
Publisher: Zenodo
Date: 2016
Publisher: Zenodo
Date: 2018
Publisher: Oxford University Press (OUP)
Date: 29-04-2022
Abstract: The study of magnetism in stars close to the transition from fossil to dynamo magnetic fields is important for understanding the nature of the stellar dynamo and dynamics of the outer atmosphere. We present surface magnetic maps for two stars that are located on opposite sides of the suspected transition zone: the chemically peculiar late A-star β Coronae Borealis (A9SrEuCr) and the early F-star σ Bootis (F3V). The large-scale magnetic field reconstructed at six epochs for β Coronae Borealis shows a complex fossil magnetic field, which is highly poloidal, and contains almost half the magnetic energy in higher multipoles (ℓ & 1). In contrast, the single epoch magnetic map for σ Bootis contains a simple surface magnetic topology that is mostly poloidal, and predominantly dipolar, and is consistent with observations of other mature late F-stars.
Publisher: EDP Sciences
Date: 04-05-4015
Publisher: Cambridge University Press (CUP)
Date: 08-2014
DOI: 10.1017/S1743921314001926
Abstract: HD 206860 is a young planet (HN Peg b) hosting star of spectral type G0V and it has a potential debris disk around it. In this work we measure the longitudinal magnetic field of HD 206860 using spectropolarimetric data and we measure the chromospheric activity using Ca II H& K, H-alpha and Ca II infrared triplet lines.
Publisher: Oxford University Press (OUP)
Date: 03-02-2020
Abstract: Helicity is a fundamental property of a magnetic field but to date it has only been possible to observe its evolution in one star – the Sun. In this paper, we provide a simple technique for mapping the large-scale helicity density across the surface of any star using only observable quantities: the poloidal and toroidal magnetic field components (which can be determined from Zeeman–Doppler imaging) and the stellar radius. We use a s le of 51 stars across a mass range of 0.1–1.34 M⊙ to show how the helicity density relates to stellar mass, Rossby number, magnetic energy, and age. We find that the large-scale helicity density increases with decreasing Rossby number Ro, peaking at Ro ≃ 0.1, with a saturation or decrease below that. For both fully and partially convective stars, we find that the mean absolute helicity density scales with the mean squared toroidal magnetic flux density according to the power law: $|\langle {h\, }\rangle |$ ∝ $\langle {\rm {{\it B}_{tor}}^2_{}\, \rangle }^{0.86\, \pm \, 0.04}$. The scatter in this relation is consistent with the variation across a solar cycle, which we compute using simulations and observations across solar cycles 23 and 24, respectively. We find a significant decrease in helicity density with age.
Publisher: EDP Sciences
Date: 09-2014
Publisher: Oxford University Press (OUP)
Date: 17-11-2016
Publisher: Oxford University Press (OUP)
Date: 11-05-2005
Publisher: EDP Sciences
Date: 24-09-2007
Publisher: Wiley
Date: 18-06-2010
Publisher: Oxford University Press (OUP)
Date: 09-12-2021
Abstract: We present wind models of 10 young Solar-type stars in the Hercules-Lyra association and the Coma Berenices cluster aged around ∼0.26 and ∼0.58 Gyr, respectively. Combined with five previously modelled stars in the Hyades cluster, aged ∼0.63 Gyr, we obtain a large atlas of 15 observationally based wind models. We find varied geometries, multi-armed structures in the equatorial plane, and a greater spread in quantities such as the angular momentum loss. In our models, we infer variation of a factor of ∼6 in wind angular momentum loss $\\dot{J}$ and a factor of ∼2 in wind mass-loss $\\dot{M}$ based on magnetic field geometry differences when adjusting for the unsigned surface magnetic flux. We observe a large variation factor of ∼4 in wind pressure for an Earth-like planet we attribute this to variations in the ‘magnetic inclination’ of the magnetic dipole axis with respect to the stellar axis of rotation. Within our models, we observe a tight correlation between unsigned open magnetic flux and angular momentum loss. To account for possible underreporting of the observed magnetic field strength we investigate a second series of wind models where the magnetic field has been scaled by a factor of 5. This gives $\\dot{M}\\propto B^{0.4}$ and $\\dot{J}\\propto B^{1.0}$ as a result of pure magnetic scaling.
Publisher: EDP Sciences
Date: 04-2021
DOI: 10.1051/0004-6361/202040027
Abstract: Aims. We report on observations of the active K2 dwarf ϵ Eridani based on contemporaneous SPIRou, NARVAL and TESS data obtained over two months in late 2018, when the activity of the star was reported to be in a non-cyclic phase. Methods. Near-infrared (NIR) spectropolarimetry was obtained using SPIRou over four nights in late September, while visible spectropolarimetry was collected with NARVAL over 20 nights, spread between 18 September and 07 November. We first recovered the fundamental parameters of the target from both visible and NIR spectral fitting. The large-scale magnetic field was investigated from polarimetric data. From unpolarized spectra, we estimated the total magnetic flux through Zeeman broadening of magnetically sensitive NIR lines and the chromospheric emission using the CaII H& K lines. The photometric monitoring, secured with TESS between 19 October and 15 November, is modelled with pseudo-periodic Gaussian process regression. Results. Fundamental parameters of ϵ Eridani derived from visible and NIR wavelengths provide us with consistent results, which also agree with published values. We report a progressive increase of macroturbulence towards larger NIR wavelengths. Zeeman broadening of in idual lines highlights an unsigned surface magnetic field B mono = 1.90 ± 0.13 kG, with a filling factor f = 12.5 ± 1.7% (unsigned magnetic flux Bf = 237 ± 36 G). The large-scale magnetic field geometry, chromospheric emission and broadband photometry display clear signs of non-rotational evolution over the course of data collection. Characteristic decay times deduced from the light curve and longitudinal field fall in the range 30–40 days, while the characteristic timescale of surface differential rotation, as derived through the evolution of the magnetic geometry, is equal to 57 ± 5 days. The large-scale magnetic field exhibits a combination of properties not observed previously for ϵ Eridani, with a surface field among the weakest previously reported, but this field is also mostly axisymmetric, and is dominated by a toroidal component.
Publisher: Cambridge University Press (CUP)
Date: 08-2014
DOI: 10.1017/S1743921314001896
Abstract: As part of the Bcool project, over 150 solar-type stars chosen mainly from planet search databases have been observed between 2006 and 2013 using the NARVAL and ESPaDOnS spectropolarimeters on the Telescope Bernard Lyot (Pic du Midi, France) and the Canada France Hawaii Telescope (Mauna Kea, USA), respectively. These single “snapshot” observations have been used to detect the presence of magnetic fields on 40% of our s le, with the highest detection rates occurring for the youngest stars. From our observations we have determined the mean surface longitudinal field (or an upper limit for stars without detections) and the chromospheric surface fluxes, and find that the upper envelope of the absolute value of the mean surface longitudinal field is directly correlated to the chromospheric emission from the star and increases with rotation rate and decreases with age.
Publisher: Oxford University Press (OUP)
Date: 10-05-2022
Abstract: Spectropolarimetric data allow for simultaneous monitoring of stellar chromospheric $\log {R^{\prime }_{\rm {HK}}}$ activity and the surface-averaged longitudinal magnetic field, Bl, giving the opportunity to probe the relationship between large-scale stellar magnetic fields and chromospheric manifestations of magnetism. We present $\log {R^{\prime }_{\rm {HK}}}$ and/or Bl measurements for 954 mid-F to mid-M stars derived from spectropolarimetric observations contained within the PolarBase database. Our magnetically active s le complements previous stellar activity surveys that focus on inactive planet-search targets. We find a positive correlation between mean $\log {R^{\prime }_{\rm {HK}}}$ and mean log |Bl|, but for G stars the relationship may undergo a change between $\log {R^{\prime }_{\rm {HK}}}\sim -4.4$ and −4.8. The mean $\log {R^{\prime }_{\rm {HK}}}$ shows a similar change with respect to the $\log {R^{\prime }_{\rm {HK}}}$ variability litude for intermediately active G stars. We also combine our results with archival chromospheric activity data and published observations of large-scale magnetic field geometries derived using Zeeman–Doppler Imaging. The chromospheric activity data indicate a slight under-density of late-F to early-K stars with $-4.75\le \log {R^{\prime }_{\rm HK}}\le -4.5$. This is not as prominent as the original Vaughan–Preston gap, and we do not detect similar under-populated regions in the distributions of the mean |Bl|, or the Bl and $\log {R^{\prime }_{\rm HK}}$ variability litudes. Chromospheric activity, activity variability, and toroidal field strength decrease on the main sequence as rotation slows. For G stars, the disappearance of dominant toroidal fields occurs at a similar chromospheric activity level as the change in the relationships between chromospheric activity, activity variability, and mean field strength.
Publisher: Oxford University Press (OUP)
Date: 21-10-2009
Publisher: Oxford University Press (OUP)
Date: 16-01-2019
Publisher: American Astronomical Society
Date: 21-09-2023
Publisher: Wiley
Date: 12-2007
Publisher: Oxford University Press (OUP)
Date: 04-2011
Publisher: Oxford University Press (OUP)
Date: 06-06-2008
DOI: 10.1111/J.1365-2966.2008.13196.X
Abstract: We present the first maps of the surface magnetic fields of a pre-main-sequence binary system. Spectropolarimetric observations of the young, 18 Myr, HD 155555 (V824 Ara, G5IV+K0IV) system were obtained at the Anglo-Australian Telescope in 2004 and 2007. Both data sets are analysed using a new binary Zeeman–Doppler imaging (ZDI) code. This allows us to simultaneously model the contribution of each component to the observed circularly polarized spectra. Stellar brightness maps are also produced for HD 155555 and compared to previous Doppler images. Our radial magnetic maps reveal a complex surface magnetic topology with mixed polarities at all latitudes. We find rings of azimuthal field on both stars, most of which are found to be non-axisymmetric with the stellar rotational axis. We also examine the field strength and the relative fraction of magnetic energy stored in the radial and azimuthal field components at both epochs. A marked weakening of the field strength of the secondary star is observed between the 2004 and 2007 epochs. This is accompanied by an apparent shift in the location of magnetic energy from the azimuthal to radial field. We suggest that this could be indicative of a magnetic activity cycle. We use the radial magnetic maps to extrapolate the coronal field (by assuming a potential field) for each star in idually – at present ignoring any possible interaction. The secondary star is found to exhibit an extreme tilt (≈75°) of its large-scale magnetic field to that of its rotation axis for both epochs. The field complexity that is apparent in the surface maps persists out to a significant fraction of the binary separation. Any interaction between the fields of the two stars is therefore likely to be complex also. Modelling this would require a full binary field extrapolation.
Publisher: Oxford University Press (OUP)
Date: 02-06-2023
Abstract: Solar-type stars, which shed angular momentum via magnetized stellar winds, enter the main sequence with a wide range of rotational periods Prot. This initially wide range of rotational periods contracts and has mostly vanished by a stellar age $t\\sim {0.6}\\, {\\rm Gyr}$, after which Solar-type stars spin according to the Skumanich relation $P_\\text{rot}\\propto \\sqrt{t}$. Magnetohydrodynamic stellar wind models can improve our understanding of this convergence of rotation periods. We present wind models of 15 young Solar-type stars aged ∼24 Myr to ∼0.13 Gyr. With our previous wind models of stars aged ∼0.26 and ∼0.6 Gyr we obtain 30 consistent three-dimensional wind models of stars mapped with Zeeman–Doppler imaging – the largest such set to date. The models provide good cover of the pre-Skumanich phase of stellar spin-down in terms of rotation, magnetic field, and age. We find the mass-loss rate $\\dot{M}\\propto \\Phi ^{{0.9\\pm 0.1}}$ with a residual spread of ∼150 per cent and the wind angular momentum loss rate $\\dot{J}\\propto {}P_\\text{rot}^{-1} \\Phi ^{1.3\\pm 0.2}$ with a residual spread of ∼500 per cent where Φ is the unsigned surface magnetic flux. When comparing different magnetic field scalings for each single star we find a gradual reduction in the power-law exponent with increasing magnetic field strength.
Publisher: Zenodo
Date: 2021
Publisher: American Astronomical Society
Date: 28-04-2023
Abstract: During the first half of their main-sequence lifetimes, stars rapidly lose angular momentum to their magnetized winds, a process known as magnetic braking. Recent observations suggest a substantial decrease in the magnetic braking efficiency when stars reach a critical value of the Rossby number, the stellar rotation period normalized by the convective overturn timescale. Cooler stars have deeper convection zones with longer overturn times, reaching this critical Rossby number at slower rotation rates. The nature and timing of the transition to weakened magnetic braking have previously been constrained by several solar analogs and two slightly hotter stars. In this Letter, we derive the first direct constraints from stars cooler than the Sun. We present new spectropolarimetry of the old G8 dwarf τ Cet from the Large Binocular Telescope, and we reanalyze a published Zeeman Doppler image of the younger G8 star 61 UMa, yielding the large-scale magnetic field strengths and morphologies. We estimate mass-loss rates using archival X-ray observations and inferences from Ly α measurements, and we adopt other stellar properties from asteroseismology and spectral energy distribution fitting. The resulting calculations of the wind braking torque demonstrate that the rate of angular momentum loss drops by a factor of 300 between the ages of these two stars (1.4–9 Gyr), well above theoretical expectations. We summarize the available data to help constrain the value of the critical Rossby number, and we identify a new signature of the long-period detection edge in recent measurements from the Kepler mission.
Publisher: Zenodo
Date: 2021
Publisher: AIP
Date: 2009
DOI: 10.1063/1.3099217
Publisher: EDP Sciences
Date: 10-12-2015
Publisher: Oxford University Press (OUP)
Date: 30-03-2016
DOI: 10.1093/MNRAS/STW731
Publisher: Oxford University Press (OUP)
Date: 14-03-2015
DOI: 10.1093/MNRAS/STV006
Publisher: Oxford University Press (OUP)
Date: 18-12-2012
DOI: 10.1093/MNRAS/STS383
Publisher: Oxford University Press (OUP)
Date: 29-11-2018
Publisher: American Meteorological Society
Date: 06-1998
Publisher: Springer Science and Business Media LLC
Date: 29-08-2006
Publisher: Cambridge University Press (CUP)
Date: 08-2014
DOI: 10.1017/S1743921314001902
Abstract: κ 1 Cet (HD 20630, HIP 15457, d = 9.16 pc, V = 4.84) is a dwarf star approximately 30 light-years away in the equatorial constellation of Cetus. Among the solar proxies studied in the Sun in Time, κ 1 Cet stands out as potentially having a mass very close to solar and a young age. On this study, we monitored the magnetic field and the chromospheric activity from the Ca II H & K lines of κ 1 Cet. We used the technique of Least-Square-Deconvolution (LSD, Donati et al. 1997) by simultaneously extracting the information contained in all 8,000 photospheric lines of the echelogram (for a linelist matching an atmospheric model of spectral type K1). To reconstruct a reliable magnetic map and characterize the surface differential rotation of κ 1 Cet we used 14 exposures spread over 2 months, in order to cover at least two rotational cycles (Prot ~9.2 days). The Least Square deconvolution (LSD) technique was applied to detect the Zeeman signature of the magnetic field in each of our 14 observations and to measure its longitudinal component. In order to reconstruct the magnetic field geometry of κ 1 Cet, we applied the Zeeman Doppler Imaging (ZDI) inversion method. ZDI revealed a structure in the radial magnetic field consisting of a polar magnetic spot. On this study, we present the fisrt look results of a high-resolution spectropolarimetric c aign to characterize the activity and the magnetic fields of this young solar proxy.
Publisher: Oxford University Press (OUP)
Date: 07-2004
Publisher: Oxford University Press (OUP)
Date: 05-07-2018
Publisher: Oxford University Press (OUP)
Date: 27-07-2017
Abstract: The young and magnetically active K dwarf ε Eridani exhibits a chromospheric activity cycle of about 3 yr. Previous reconstructions of its large-scale magnetic field show strong variations at yearly epochs. To understand how ε Eridani’s large-scale magnetic field geometry evolves over its activity cycle, we focus on high-cadence observations spanning 5 months at its activity minimum. Over this time-span, we reconstruct three maps of ε Eridani’s large-scale magnetic field using the tomographic technique of Zeeman–Doppler imaging. The results show that at the minimum of its cycle, ε Eridani’s large-scale field is more complex than the simple dipolar structure of the Sun and 61 Cyg A at minimum. Additionally, we observe a surprisingly rapid regeneration of a strong axisymmetric toroidal field as ε Eridani emerges from its S-index activity minimum. Our results show that all stars do not exhibit the same field geometry as the Sun, and this will be an important constraint for the dynamo models of active solar-type stars.
Publisher: American Astronomical Society
Date: 27-11-2019
Publisher: Cambridge University Press (CUP)
Date: 2001
DOI: 10.1071/AS01028
Abstract: The Algol type eclipsing binary KZ Pav has been observed over one complete orbit (0.95 days) with theAustraliaTelescope CompactArray. Contemporaneous optical photometric data from the University of Southern Queensland’s Observatory at Mount Kent were also collected and have been included in this multi-wavelength study. Preliminary indications are that the low levels of emission observed share similarities to those of some RS CVn binaries. The optical data show phase-linked effects which can be related to the mass transfer process of Algols. The possibility that the radio emission may be related to this process is considered.
Publisher: Oxford University Press (OUP)
Date: 15-01-2020
Abstract: Little is known of the activity and differential rotation of low luminosity, early M dwarfs from direct observation. We present the first stellar activity analysis of star-spots and faculae for the hot Jupiter hosting M1V dwarf Kepler-45 from $\\it Kepler$ transit light curves. We find star-spot and facula temperatures contrasting a few hundred degrees with the quiet photosphere, hence similar to other early M dwarfs having a convective envelope surrounding a radiative core. Star-spots are prominent close to the centre of the stellar disc, with faculae prominent towards the limbs, similar to what is observed for the Sun. Star-spot and facula mean sizes are about 40 and 45 × 103 km, respectively, and thus faculae occupy a 10 per cent larger surface area than the star-spots. A short-term activity cycle of about 295 d is observed that is reminiscent of those seen for other cool dwarfs. Adopting a solar-type differential rotation profile (faster equatorial rotation than polar rotation), our star-spot and facula temporal mapping indicates a rotation period of 15.520 ± 0.025 d at the transit latitude of −33.2°. From the mean stellar rotation of 15.762 d, we estimate a rotational shear of 0.031 ± 0.004 rad d−1, or a relative differential rotation of 7.8 ± 0.9 per cent. Kepler-45’s surface rotational shear is thus consistent with observations and theoretical modelling of other early M dwarfs that indicate a shear of less than 0.045 rad d−1 and no less than 0.03 rad d−1 for stars with similar stellar rotation periods.
Publisher: Oxford University Press (OUP)
Date: 21-07-2006
Publisher: Oxford University Press (OUP)
Date: 19-05-2014
DOI: 10.1093/MNRAS/STU728
Publisher: Oxford University Press (OUP)
Date: 18-12-2012
DOI: 10.1093/MNRAS/STS384
Publisher: Oxford University Press (OUP)
Date: 17-09-2015
Publisher: Zenodo
Date: 2018
Publisher: Oxford University Press (OUP)
Date: 23-10-2016
Publisher: Oxford University Press (OUP)
Date: 11-11-2003
Publisher: Wiley
Date: 12-2011
Abstract: A s le of 19 solar‐type stars, probing masses between 0.6 and 1.4 solar masses and rotation periods between 3.4 and 43 days, was regularly observed using the NARVAL spectropolarimeter at Telescope Bernard Lyot (Pic du Midi, France) between 2007 and 2011. The Zeeman‐Doppler Imaging technique is employed to reconstruct the large‐scale photospheric magnetic field structure of the targets and investigate its long‐term temporal evolution. We present here the first results of this project with the observation of short magnetic cycles in several stars, showing up a succession of polarity reversals over the timespan of our monitoring. Preliminary trends suggest that short cycles are more frequent for stellar periods below a dozen days and for stellar masses above about one solar mass. The cycles lengths unveiled by the direct tracking of polarity switches are significantly shorter than those derived from previous studies based on chromospheric activity monitoring, suggesting the coexistence of several magnetic timescales in a same star (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: EDP Sciences
Date: 19-01-2015
Publisher: Oxford University Press (OUP)
Date: 05-2008
Publisher: Zenodo
Date: 2021
Publisher: IOP Publishing
Date: 26-09-2019
Publisher: EDP Sciences
Date: 29-10-2020
DOI: 10.1051/0004-6361/202037693
Abstract: Context. Young solar analogs reaching the main sequence experience very strong magnetic activity, generating angular momentum losses through wind and mass ejections. Aims. We investigate signatures of magnetic fields and activity at the surface and in the prominence system of the ultra-rapid rotator V530 Per, a G-type solar-like member of the young open cluster α Persei. This object has a rotation period that is shorter than all stars with available magnetic maps. Methods. With a time-series of spectropolarimetric observations gathered with ESPaDOnS over two nights on the Canada-France-Hawaii Telescope, we reconstructed the surface brightness and large-scale magnetic field of V530 Per using the Zeeman-Doppler imaging method, assuming an oblate stellar surface. We also estimated the short term evolution of the brightness distribution through latitudinal differential rotation. Using the same data set, we finally mapped the spatial distribution of prominences through tomography of the H α emission. Results. The brightness map is dominated by a large, dark spot near the pole, accompanied by a complex distribution of bright and dark features at lower latitudes. Taking the brightness map into account, the magnetic field map is reconstructed as well. Most of the large-scale magnetic field energy is stored in the toroidal field component. The main radial field structure is a positive region of about 500 G, at the location of the dark polar spot. The brightness map of V530 Per is sheared by solar-like differential rotation, with roughly a solar value for the difference in rotation rate between the pole and equator. It is important to note that H α is observed in emission and it is mostly modulated by the stellar rotation period over one night. The prominence system is organized in a ring at the approximate location of the corotation radius, and displays significant evolution between the two observing nights. Conclusions. V530 Per is the first ex le of a solar-type star to have its surface magnetic field and prominences mapped together, which will bring important observational constraints to better understand the role of slingshot prominences in the angular momentum evolution of the most active stars.
Publisher: Oxford University Press (OUP)
Date: 02-06-2021
Abstract: Short-orbit gas giant planet formation/evolution mechanisms are still not well understood. One promising pathway to discriminate between mechanisms is to constrain the occurrence rate of these peculiar exoplanets at the earliest stage of the system’s life. However, a major limitation when studying newly born stars is stellar activity. This cocktail of phenomena triggered by fast rotation, strong magnetic fields, and complex internal dynamics, especially present in very young stars, compromises our ability to detect exoplanets. In this paper, we investigated the limitations of such detections in the context of already acquired data solely using radial velocity data acquired with a non-stabilized spectrograph. We employed two strategies: Doppler Imaging and Gaussian Processes and could confidently detect hot Jupiters with a semi- litude of 100 m s−1 buried in the stellar activity. We also showed the advantages of the Gaussian Process approach in this case. This study serves as a proof of concept to identify potential candidates for follow-up observations or even discover such planets in legacy data sets available to the community.
Publisher: EDP Sciences
Date: 12-2018
DOI: 10.1051/0004-6361/201834347
Abstract: Context. The behaviour of the large-scale dipolar field, during a star’s magnetic cycle, can provide valuable insight into the stellar dynamo and associated magnetic field manifestations such as stellar winds. Aims. We investigate the temporal evolution of the dipolar field of the K dwarf 61 Cyg A using spectropolarimetric observations covering nearly one magnetic cycle equivalent to two chromospheric activity cycles. Methods. The large-scale magnetic field geometry is reconstructed using Zeeman Doppler imaging, a tomographic inversion technique. Additionally, the chromospheric activity is also monitored. Results. The observations provide an unprecedented s ling of the large-scale field over a single magnetic cycle of a star other than the Sun. Our results show that 61 Cyg A has a dominant dipolar geometry except at chromospheric activity maximum. The dipole axis migrates from the southern to the northern hemisphere during the magnetic cycle. It is located at higher latitudes at chromospheric activity cycle minimum and at middle latitudes during cycle maximum. The dipole is strongest at activity cycle minimum and much weaker at activity cycle maximum. Conclusions. The behaviour of the large-scale dipolar field during the magnetic cycle resembles the solar magnetic cycle. Our results are further confirmation that 61 Cyg A indeed has a large-scale magnetic geometry that is comparable to the Sun’s, despite being a slightly older and cooler K dwarf.
Publisher: Oxford University Press (OUP)
Date: 29-09-2021
Abstract: The evolution in latitude of sunspots is a key feature of the cyclic solar dynamo. Here, we present the results of a spectroscopic and spectropolarimetric monitoring c aign on the young (∼20 Myr old) early G star HIP 89829, in order to investigate potential evolution in the distribution of the star’s spots and magnetic features. Our analysis of this G5V star spans eight epochs, from June 2010 to August 2015. The techniques of Doppler imaging and Zeeman–Doppler imaging were used to create brightness maps for each epoch and magnetic maps for two epochs. The brightness images show the star to have stable spot features with two main spot latitudes – a polar spot, often seen on young rapidly rotating stars such as this, and another highly unusual group of large spot features around the 20° and 30° latitudes. These lower spot latitudes appear to be rather stable over the 5 yr of observations. We included a solar-type differential rotation law into the imaging process and measured near-solid-body rotation for epochs where sufficient data exist for this analysis. The magnetic features show a dominant poloidal and a weaker toroidal magnetic field for both Stokes V epochs, which is unusual for a star with a rapid rotation period of 0.57 d. We conclude that HIP 89829 is an active young solar-type star with long-lived spots and near-solid-body rotation.
Publisher: Oxford University Press (OUP)
Date: 29-10-2015
Publisher: American Astronomical Society
Date: 11-2021
Abstract: HIP 67522 b is a 17 Myr old, close-in ( P orb = 6.96 days), Jupiter-sized ( R = 10 R ⊕ ) transiting planet orbiting a Sun-like star in the Sco–Cen OB association. We present our measurement of the system’s projected orbital obliquity via two spectroscopic transit observations using the CHIRON spectroscopic facility. We present a global model that accounts for large surface brightness features typical of such young stars during spectroscopic transit observations. With a value of ∣ λ ∣ = 5.8 − 5.7 + 2.8 ° it is unlikely that this well-aligned system is the result of a high-eccentricity-driven migration history. By being the youngest planet with a known obliquity, HIP 67522 b holds a special place in contributing to our understanding of giant planet formation and evolution. Our analysis shows the feasibility of such measurements for young and very active stars.
Publisher: Oxford University Press (OUP)
Date: 13-03-2023
Abstract: The early, active history of our Sun is still not fully understood. Observations of the magnetic fields on active young solar-type stars allow us an insight into the early evolution of our Sun. Here we present Doppler and Zeeman–Doppler images of the young late-F star HIP 71933 (HD 129181) at multiple epochs to add to the growing data about the evolution of magnetic cycles in solar-type stars. Spectroscopic data were obtained over seven epochs spanning 10 yr of observations, with two epochs including spectropolarimetric data. The brightness maps at all epochs show a consistent spot activity in a non-uniform ring at a latitude of approximately +60° with no polar spot present in any epoch. The two magnetic field maps taken ∼2 yr apart show a strong poloidal field configuration with most of the poloidal field energy in the dipolar configuration. The magnetic maps show no evidence of a polarity reversal. We were able to measure the differential rotation from one of the seven epochs using the brightness data finding a dΩ of 0.325 ± 0.01 rad d−1. The values for the rotational period and differential rotation found for HIP 71933 are consistent with values found for other late-F or early-G stars. The dominant poloidal features and the limited spots at the pole are unusual for a rapidly rotating star but not unique.
Publisher: Oxford University Press (OUP)
Date: 22-01-2016
Publisher: Cambridge University Press (CUP)
Date: 10-2016
DOI: 10.1017/S1743921317004276
Abstract: Among the solar proxies, κ 1 Cet, stands out as potentially having a mass very close to solar and a young age. We report magnetic field measurements and planetary habitability consequences around this star, a proxy of the young Sun when life arose on Earth. Magnetic strength was determined from spectropolarimetric observations and we reconstruct the large-scale surface magnetic field to derive the magnetic environment, stellar winds, and particle flux permeating the interplanetary medium around κ 1 Cet. Our results show a closer magnetosphere and mass-loss rate 50 times larger than the current solar wind mass-loss rate when Life arose on Earth, resulting in a larger interaction via space weather disturbances between the stellar wind and a hypothetical young-Earth analogue, potentially affecting the habitability. Interaction of the wind from the young Sun with the planetary ancient magnetic field may have affected the young Earth and its life conditions.
Publisher: Cambridge University Press (CUP)
Date: 08-2010
DOI: 10.1017/S1743921309992535
Abstract: A key part of the modern-day regenerative solar magnetic dynamo is the reversal of the Sun's global magnetic field every eleven years. However, recent theoretical models indicate that young-rapidly rotating Sun-like stars may not always undergo full magnetic reversals, but instead may sometimes undergo “attempted” reversals where the magnetic field declines in strength only to return with the same polarity. Using the technique of Zeeman Doppler imaging we have mapped the magnetic field topology of a small s le of young Sun-like stars at multiple epochs, and present tentative evidence of an “attempted” magnetic field reversal on one of our stars.
Publisher: American Astronomical Society
Date: 09-05-2019
Publisher: Wiley
Date: 02-2013
Abstract: Astrophysical plasmas and magnetic fields are inextricably coupled to each other. But magnetic fields are elusive they cannot be fully characterized with standard (spectroscopic) observational techniques. Fortunately, polarisation, the third fundamental property of light, encodes all the quantitative information on the magnetism of the objects we observe. This splinter session brought together the solar and stellar spectropolarimetric communities to discuss some of the fundamental unsolved questions of solar and stellar magnetism and the future of spectropolarimetric observations. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: Oxford University Press (OUP)
Date: 17-04-2019
Publisher: Oxford University Press (OUP)
Date: 09-10-2020
Publisher: Oxford University Press (OUP)
Date: 23-11-2011
Publisher: Oxford University Press (OUP)
Date: 28-12-2020
Abstract: We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA’s Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the Minerva-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of MP = 0.138 ± 0.023 $\\rm {M_J}$ (43.9 ± 7.3 $\\, M_{\\rm \\oplus}$), a radius of RP = 0.639 ± 0.013 $\\rm {R_J}$ (7.16 ± 0.15 $\\, \\mathrm{ R}_{\\rm \\oplus}$), bulk density of $0.65^{+0.12}_{-0.11}$ (cgs), and period $18.38818^{+0.00085}_{-0.00084}$ $\\rm {days}$. TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M* = 1.390 ± 0.046 $\\rm {M_{sun}}$, R* = 1.888 ± 0.033 $\\rm {R_{sun}}$, Teff = 6075 ± 90 $\\rm {K}$, and vsin i = 11.3 ± 0.5 km s−1. Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a ∼71 day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (∼100) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known s le of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.
Publisher: Oxford University Press (OUP)
Date: 11-07-2008
Publisher: Oxford University Press (OUP)
Date: 16-06-2021
Abstract: Stellar winds govern the spin-down of Solar-type stars as they age, and play an important role in determining planetary habitability, as powerful winds can lead to atmospheric erosion. We calculate 3D stellar wind models for five young Solar-type stars in the Hyades cluster, using TOUPIES survey stellar magnetograms and state-of-the-art Alfvén wave-driven wind modelling. The stars have the same 0.6 Gyr age and similar fundamental parameters, and we account for the uncertainty in and underestimation of absolute field strength inherent in Zeeman–Doppler imaging by adopting both unscaled and scaled (by a factor of five) field strengths. For the unscaled fields, the resulting stellar wind mass-loss is 2–4 times greater and the angular momentum loss 2–10 times greater than for the Sun today, with the scaled results correspondingly greater. We compare our results with a range published of wind models and for the Alfvén wave-driven modelling see evidence of mass-loss saturation at ${\\sim 10} \\dot{M}_{\\odot }$.
Publisher: Oxford University Press (OUP)
Date: 27-10-2016
Publisher: EDP Sciences
Date: 30-01-2019
DOI: 10.1051/0004-6361/201833545
Abstract: Context . The origin of the fossil magnetic fields detected in 5 to 10% of intermediate-mass main sequence stars is still highly debated. Aims . We want to bring observational constraints to a large population of intermediate-mass pre-main sequence (PMS) stars in order to test the theory that convective-dynamo fields generated during the PMS phases of stellar evolution can occasionally relax into fossil fields on the main sequence. Methods . Using distance estimations, photometric measurements, and spectropolarimetric data from HARPSpol and ESPaDOnS of 38 intermediate-mass PMS stars, we determined fundamental stellar parameters ( T eff , L and v sin i ) and measured surface magnetic field characteristics (including detection limits for non-detections, and longitudinal fields and basic topologies for positive detections). Using PMS evolutionary models, we determined the mass, radius, and internal structure of these stars. We compared different PMS models to check that our determinations were not model-dependant. We then compared the magnetic characteristics of our s le accounting for their stellar parameters and internal structures. Results . We detect magnetic fields in about half of our s le. About 90% of the magnetic stars have outer convective envelopes larger than ∼25% of the stellar radii, and heavier than ∼2% of the stellar mass. Going to higher mass, we find that the magnetic incidence in intermediate-mass stars drops very quickly, within a timescale on the order of few times 0.1 Myr. Finally, we propose that intermediate-mass T Tauri stars with large convective envelopes, close to the fully convective limit, have complex fields and that their dipole component strengths may decrease as the sizes of their convective envelopes decrease, similar to lower-mass T Tauri stars.
Publisher: Oxford University Press (OUP)
Date: 24-01-2014
Publisher: IOP Publishing
Date: 05-2014
DOI: 10.1086/676976
Publisher: Wiley
Date: 03-2004
Publisher: Oxford University Press (OUP)
Date: 04-04-2012
Publisher: AIP
Date: 2009
DOI: 10.1063/1.3246492
Publisher: Cambridge University Press (CUP)
Date: 08-2014
DOI: 10.1017/S1743921314001938
Abstract: Doppler Imaging of starspots on young solar analogues is a way to investigate the early history of solar magnetic activity by proxy. Doppler images of young G-dwarfs have yielded the presence of large polar spots, extending to moderate latitudes, along with measurements of the surface differential rotation. The differential rotation measurement for one star (RX J0850.1-7554) suggests it is possibly the first ex le of a young G-type dwarf whose surface rotates as almost a solid body, in marked contrast to the differential rotation of other rapidly rotating young G-dwarfs and the present-day Sun. Overall, our Doppler imaging results show that the young Sun possessed a fundamentally different dynamo to today.
Publisher: Oxford University Press (OUP)
Date: 11-10-2017
Abstract: Magnetic activity is known to be correlated to the rotation period for moderately active main-sequence solar-like stars. In turn, the stellar rotation period evolves as a result of magnetized stellar winds that carry away angular momentum. Understanding the interplay between magnetic activity and stellar rotation is therefore a central task for stellar astrophysics. Angular momentum evolution models typically employ spin-down torques that are formulated in terms of the surface magnetic field strength. However, these formulations fail to account for the magnetic field geometry, unlike those that are expressed in terms of the open flux, i.e. the magnetic flux along which stellar winds flow. In this work, we model the angular momentum evolution of main-sequence solar-mass stars using a torque law formulated in terms of the open flux. This is done using a potential field source surface model in conjunction with the Zeeman–Doppler magnetograms of a s le of roughly solar-mass stars. We explore how the open flux of these stars varies with stellar rotation and choice of source surface radii. We also explore the effect of field geometry by using two methods of determining the open flux. The first method only accounts for the dipole component while the second accounts for the full set of spherical harmonics available in the Zeeman–Doppler magnetogram. We find only a small difference between the two methods, demonstrating that the open flux, and indeed the spin-down, of main-sequence solar-mass stars is likely dominated by the dipolar component of the magnetic field.
Publisher: Oxford University Press (OUP)
Date: 08-2000
Publisher: Cambridge University Press (CUP)
Date: 08-2013
DOI: 10.1017/S174392131400221X
Abstract: The habitable zone is the range of orbital distances from a host star in which an exoplanet would have a surface temperature suitable for maintaining liquid water. This makes the orbital distance of exoplanets an important variable when searching for extra-solar Earth analogues. However, the orbital distance is not the only important factor determining whether an exoplanet is potentially suitable for life. The ability of an exoplanet to retain an atmosphere is also vital since it helps regulate surface temperatures. One mechanism by which a planetary atmosphere can be lost is erosion due to a strong stellar wind from the host star. The presence of a magnetosphere can help to shield a planetary atmosphere from this process. Using a simple stellar wind model, we present the impact that stellar winds might have on magnetospheric sizes of exoplanets. This is done with the aim of further constraining the parameter space in which we look for extra-solar Earth analogues.
Publisher: Oxford University Press (OUP)
Date: 03-01-2022
Abstract: The Kepler mission target star KOI-883 is notable in being a low-mass K2V dwarf with moderately fast 8.99-d rotation and hosting a single transiting hot Jupiter in a 2.69-d orbit. This combination thus presents a particular opportunity to study star-spot activity by using the many deep planetary transits apparent in the light curve to map the stellar surface. The data have been analysed using spot modelling and temporal mapping methods we have used for other Kepler host stars, and a search for flares was conducted. Our results indicate a low-latitude region of the photosphere marked by distinct areas of in idual or grouped star-spots with moderately high solar-type differential rotation of 0.102 ± 0.011 rad d−1, but with just two major flares observed across 400 d. These results imply a rotational shear significantly greater than that of our slower rotating Sun. The observed flares are more energetic than typical solar flares, but similar to those of other magnetically active cool dwarfs.
Publisher: American Astronomical Society
Date: 16-03-2016
Publisher: American Astronomical Society
Date: 17-11-2005
DOI: 10.1086/498941
Publisher: American Astronomical Society
Date: 22-02-2023
Abstract: We report the discovery of TOI-4562b (TIC-349576261), a Jovian planet orbiting a young F7V-type star, younger than the Praesepe/Hyades clusters ( Myr). This planet stands out because of its unusually long orbital period for transiting planets with known masses ( P orb = 225.11781 − 0.00022 + 0.00025 days) and because it has a substantial eccentricity ( e = 0.76 − 0.02 + 0.02 ). The location of TOI-4562 near the southern continuous viewing zone of TESS allowed observations throughout 25 sectors, enabling an unambiguous period measurement from TESS alone. Alongside the four available TESS transits, we performed follow-up photometry using the South African Astronomical Observatory node of the Las Cumbres Observatory and spectroscopy with the CHIRON spectrograph on the 1.5 m SMARTS telescope. We measure a radius of 1.118 + 0.013 − 0.014 R J and a mass of 2.30 − 0.47 + 0.48 M J for TOI-4562b. The radius of the planet is consistent with contraction models describing the early evolution of the size of giant planets. We detect tentative transit timing variations at the ∼20 minutes level from five transit events, favoring the presence of a companion that could explain the dynamical history of this system if confirmed by future follow-up observations. With its current orbital configuration, tidal timescales are too long for TOI-4562b to become a hot Jupiter via high-eccentricity migration though it is not excluded that interactions with the possible companion could modify TOI-4562b’s eccentricity and trigger circularization. The characterization of more such young systems is essential to set constraints on models describing giant-planet evolution.
Publisher: Cambridge University Press (CUP)
Date: 1997
DOI: 10.1071/AS97274
Abstract: The Monash University Physics Department is constructing a spectrograph, to be attached to a 0·46-m Cassegrainian telescope. To help future users of the spectrograph determine the operational capabilities of the spectrograph a PC-based software package was created. This program allows the user to simulate the response of the spectrograph to various stellar types under differing observational constraints. We have estimated the precision of measurements of stellar radial velocities with the spectrograph. The estimates are reasonable but are yet to be compared with real data.
Publisher: Oxford University Press (OUP)
Date: 29-03-2023
Abstract: F stars lie in the transition region between cool stars with dynamo generated fields and hot star fossil fields and offer an interesting window into the generation of magnetic fields in shallow convection zones. In this paper, we investigate the magnetic field of the mature F7V primary of the bright χ Draconis system. χ Dra was observed in circularly polarized light at four epochs from 2014 through to 2019 using the NARVAL spectropolarimeter at the Téléscope Bernard Lyot. Using the technique of least-squares deconvolution, we created high signal-to-noise line profiles from which we were able to measure the radial velocity of both the primary and secondary and use these to improve the orbital parameters of the system. Additionally, we used the technique of Zeeman Doppler imaging to reconstruct the large-scale magnetic field geometry of the primary at the four epochs. The magnetic maps show that χ Dra A has a predominately dipolar poloidal magnetic field at all epochs with the magnetic axis well aligned with the stellar rotation axis. The large-scale features of the magnetic field appear to be relatively stable over the ∼5 yr time base of our observations, with no evidence of any polarity reversals. We used the magnetic field maps to model the wind from χ Dra A at all epochs, showing that the mass-loss from the stellar wind of χ Dra A is 3–6 times the current solar value, while the angular momentum loss from the wind is around 3–4 times the solar value.
Publisher: EDP Sciences
Date: 24-11-2015
Publisher: Oxford University Press (OUP)
Date: 30-11-2016
Publisher: Zenodo
Date: 2016
Publisher: Cambridge University Press (CUP)
Date: 2011
DOI: 10.1071/AS11025
Abstract: High-resolution spectroscopy and spectropolarimetry have been undertaken at the Anglo-Australian Telescope in order to identify suitable targets for magnetic studies of young Sun-like stars, for the proxy study of early solar evolution. This study involved the investigation of some variable late F- / early G-type Sun-like stars originally identified by the Hipparcos mission. Of the 38 stars observed for this study, HIP 31021, HIP 64732, HIP 73780 were found to be spectroscopic binary stars, while HIP 19072, HIP 67651 and HIP 75636 are also likely to be binaries and HIP 33111 could even be a triple system. Magnetic fields were detected on a number of the survey stars: HIP 21632, HIP 43720, HIP 48770, HIP 62517, HIP 71933, HIP 77144, HIP 89829, HIP 90899 and HIP 105388, making these stars good candidates for follow-up Zeeman Doppler imaging studies.
Publisher: AIP
Date: 2012
DOI: 10.1063/1.3701907
Publisher: EDP Sciences
Date: 09-2012
Publisher: Cambridge University Press (CUP)
Date: 07-2004
Publisher: Zenodo
Date: 2018
Publisher: Cambridge University Press (CUP)
Date: 07-2010
DOI: 10.1017/S1743921311010295
Abstract: The ultraviolet stellar wind lines of the photometrically periodic variable early B-type star σ Lupi were found to behave very similarly to what has been observed in known magnetic B stars, although no periodicity could be determined. AAT spectropolarimetric measurements with SEMPOL were obtained. We detected a longitudinal magnetic field with varying strength and litude of about 100 G with error bars of typically 20 G. This type of variability supports an oblique magnetic rotator model. We fold the equivalent width of the 4 usable UV spectra in phase with the well-known photometric period of 3.019 days, which we identify with the rotation period of the star. The magnetic field variations are consistent with this period. Additional observations with ESPaDOnS attached to the CFHT strongly confirmed this discovery, and allowed to determine a precise magnetic period. Like in the other magnetic B stars the wind emission likely originates in the magnetic equatorial plane, with maximum emission occurring when a magnetic pole points towards the Earth. The 3.0182 d magnetic rotation period is consistent with the photometric period, with maximum light corresponding to maximum magnetic field. No helium or other chemical peculiarity is known for this object.
Publisher: Zenodo
Date: 2021
Publisher: EDP Sciences
Date: 10-2014
Publisher: Oxford University Press (OUP)
Date: 22-04-2016
DOI: 10.1093/MNRAS/STW828
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1071/AS04058
Publisher: Oxford University Press (OUP)
Date: 02-2005
Publisher: EDP Sciences
Date: 2009
DOI: 10.1051/EAS/0939007
Publisher: Oxford University Press (OUP)
Date: 11-05-2019
Publisher: Oxford University Press (OUP)
Date: 29-03-2017
DOI: 10.1093/MNRAS/STX753
Publisher: Oxford University Press (OUP)
Date: 22-11-2018
Location: Switzerland
Start Date: 06-2016
End Date: 12-2018
Amount: $800,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2009
End Date: 12-2009
Amount: $350,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2018
End Date: 07-2023
Amount: $792,859.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2016
End Date: 10-2017
Amount: $550,000.00
Funder: Australian Research Council
View Funded Activity