Modelling the magnetic activity and filtering radial velocity curves of young Suns : the weak-line T Tauri star LkCa 4

Donati, J.‐F.; Hébrard, E.; Hussain, G. A. J.; Moutou, C.; Grankin, K. N.; Boisse, I.; Morin, J.; Gregory, S. G.; Vidotto, A. A.; Bouvier, J.; Alencar, S. H. P.; Delfosse, X.; Doyon, René; Takami, M.; Jardine, M.; Farès, R.; Cameron, A. Collier; Ménard, F.; Dougados, C.; Herczeg, Gregory J.

doi:10.1093/mnras/stu1679

Cited by 78 publications

(192 citation statements)

References 38 publications

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“…One conceivable interpretation of the 74%-86% coverage fraction of cool photosphere is a stellar axis inclined towards our observing direction, with a large circumpolar spot covering much of the observable hemisphere, as described by Donati et al (2014). The ambient hot photosphere would then be close to the equator, which would be limb-darkened due to projection effects.…”

Section: Discussionmentioning

confidence: 89%

“…There is also evidence for a hot spot in the reconstructed ZDI map. These spot maps demonstrate that multiple temperature components contribute to the broadband emission from the star, which may explain the large differences between the 4100 K effective temperature measurement obtained from high-resolution optical spectra (Donati et al 2014) compared with 3600 K obtained from an analysis dominated by TiO bands (Herczeg & Hillenbrand 2014).…”

mentioning

confidence: 88%

“…Published data targeting LkCa 4 is composed of 29 BV R visits from 1985(Vrba et al 1993, 26 BV R epochs from 1990−1991 (Bouvier et al 1993), 284 visits in Vband (278 with B and 268 with R) from 1992 August -2004 October (Grankin et al 2008), and 10 BV R visits from 2013 (Donati et al 2014). ASAS3 (Pojmański 2004 Figure 2 shows all available V −band data grouped by the 22 observing seasons and phase-folded by the period P = 3.375 days obtained from multiterm Lomb-Scargle periodograms (Ivezić et al 2014).…”

Section: Photometric Monitoringmentioning

confidence: 99%

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Placing the Spotted T Tauri Star LkCa 4 on an HR Diagram

Gully-Santiago

Herczeg

Czekala

et al. 2017

ApJ

134

111

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Ages and masses of young stars are often estimated by comparing their luminosities and effective temperatures to pre-main sequence stellar evolution tracks, but magnetic fields and starspots complicate both the observations and evolution. To understand their influence, we study the heavily-spotted weak-lined T-Tauri star LkCa 4 by searching for spectral signatures of radiation originating from the starspot or starspot groups. We introduce a new methodology for constraining both the starspot filling factor and the spot temperature by fitting two-temperature stellar atmosphere models constructed from Phoenix synthetic spectra to a high-resolution near-IR IGRINS spectrum. Clearly discernable spectral features arise from both a hot photospheric component T hot ∼ 4100 K and to a cool component T cool ∼ 2700 − 3000 K, which covers ∼ 80% of the visible surface. This mix of hot and cool emission is supported by analyses of the spectral energy distribution, rotational modulation of colors and of TiO band strengths, and features in low-resolution optical/near-IR spectroscopy. Although the revised effective temperature and luminosity make LkCa 4 appear much younger and lower mass than previous estimates from unspotted stellar evolution models, appropriate estimates will require the production and adoption of spotted evolutionary models. Biases from starspots likely afflict most fully convective young stars and contribute to uncertainties in ages and age spreads of open clusters. In some spectral regions starspots act as a featureless "veiling" continuum owing to high rotational broadening and heavy line-blanketing in cool star spectra. Some evidence is also found for an anti-correlation between the velocities of the warm and cool components.

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Section: Discussionmentioning

confidence: 89%

mentioning

confidence: 88%

Section: Photometric Monitoringmentioning

confidence: 99%

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Placing the Spotted T Tauri Star LkCa 4 on an HR Diagram

Gully-Santiago

Herczeg

Czekala

et al. 2017

ApJ

134

111

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“…In Figure 6 we plot the difference as a function of spectral type between the observed RV of each candidate and the expected RV if it moved at the mean Taurus v UVW . We expect the RV distribution of bona fide single Taurus members to be inflated by several factors of 1 km s −1 , including observational uncertainties, RV jitter from stellar activity (e.g., Prato et al 2008;Donati et al 2014), the largescale velocity structure of Taurus (Bertout & Genova 2006), and the velocity power spectrum around the Taurus mean (Larson 1981). Indeed, we find that of the 86 objects that agree with comovement to within 3 km s −1 , 48 are flagged as conclusive members while only 6 are flagged as conclusive nonmembers, with 33 remaining ambiguous.…”

Section: Radial Velocitiesmentioning

confidence: 99%

The Greater Taurus–Auriga Ecosystem. I. There is a Distributed Older Population

Kraus

Herczeg

Rizzuto

et al. 2017

ApJ

158

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The census of Taurus-Auriga has been assembled over seven decades and inherited the biases and incompleteness of the input studies. The unusual shape of its inferred initial mass function (IMF) and the existence of isolated diskbearing stars suggest that additional (likely disk-free) members remain to be discovered. We therefore have begun a global reassessment of the census of Taurus-Auriga that exploits new data and better definitions of youth and kinematic membership. As a first step, we reconsider the membership of all disk-free candidate members from the literature with spectral type F0, a < < 3 50 5 40 h m h m , and d  < <  14 34 . We combine data from the literature with Keck/HIRES and UH88/SNIFS spectra to test the membership of these candidates using the positions in the Hertzsprung-Russel diagram, proper motions, radial velocities, Hα, lithium, and surface gravity. We find 218 confirmed or likely Taurus members, 160 confirmed or likely interlopers, and only 18 that lack sufficient evidence to draw firm conclusions. A significant fraction of these stars (81/218 = 37%) are not included in the most recent canonical member lists. There are few additional members to the immediate vicinity of the molecular clouds, preserving the IMFs that have been deemed anomalous in past work. Many of the likely Taurus members are instead distributed broadly across the search area. When combined with the known disk hosts, our updated census reveals two regimes: a high-density population with a high disk fraction (indicative of youth) that broadly traces the molecular clouds, and a low-density population with low disk fraction (hence likely older) that most likely represents previous generations of star formation.

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“…Dumusque et al 2014). Other studies have considered the detectability of planets around active cool stars by modelling the stellar activity from recovered starspot and magnetic field maps (Jeffers et al 2014a;Donati et al 2014). It is clear that knowing the characteristics of the stellar magnetic field is crucial for addressing the presence of exo-planets in a given system (e.g.…”

Section: Introductionmentioning

confidence: 99%

Activity and magnetic field structure of the Sun-like planet-hosting star HD 1237

Alvarado‐Gómez

Hussain

Grunhut

et al. 2015

A&A

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We analyse the magnetic activity characteristics of the planet-hosting Sun-like star, HD 1237, using HARPS spectro-polarimetric time-series data. We find evidence of rotational modulation of the magnetic longitudinal field measurements that is consistent with our ZDI analysis with a period of 7 days. We investigate the effect of customising the LSD mask to the line depths of the observed spectrum and find that it has a minimal effect on the shape of the extracted Stokes V profile but does result in a small increase in the S/N (∼7%). We find that using a Milne-Eddington solution to describe the local line profile provides a better fit to the LSD profiles in this slowly rotating star, which also affects the recovered ZDI field distribution. We also introduce a fit-stopping criterion based on the information content (entropy) of the ZDI map solution set. The recovered magnetic field maps show a strong (+90 G) ring-like azimuthal field distribution and a complex radial field dominating at mid latitudes (∼45 degrees). Similar magnetic field maps are recovered from data acquired five months apart. Future work will investigate how this surface magnetic field distribution affeccts the coronal magnetic field and extended environment around this planet-hosting star.

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Modelling the magnetic activity and filtering radial velocity curves of young Suns : the weak-line T Tauri star LkCa 4

Cited by 78 publications

References 38 publications

Placing the Spotted T Tauri Star LkCa 4 on an HR Diagram

Placing the Spotted T Tauri Star LkCa 4 on an HR Diagram

The Greater Taurus–Auriga Ecosystem. I. There is a Distributed Older Population

Activity and magnetic field structure of the Sun-like planet-hosting star HD 1237

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