The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra

L. Tal-Or; M. Zechmeister; A. Reiners; S. V. Jeffers; P. Schöfer; A. Quirrenbach; P. J. Amado; I. Ribas; J. A. Caballero; J. Aceituno; F. F. Bauer; V. J.S. Béjar; S. Czesla; S. Dreizler; B. Fuhrmeister; A. P. Hatzes; E. N. Johnson; M. Kürster; M. Lafarga; D. Montes; J. C. Morales; S. Reffert; S. Sadegi; W. Seifert; D. Shulyak

doi:10.1051/0004-6361/201732362

The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra

L. Tal-Or, M. Zechmeister, A. Reiners, S. V. Jeffers, P. Schöfer, A. Quirrenbach, P. J. Amado, I. Ribas, J. A. Caballero, J. Aceituno, F. F. Bauer, V. J.S. Béjar, S. Czesla, S. Dreizler, B. Fuhrmeister, A. P. Hatzes, E. N. Johnson, M. Kürster, M. Lafarga, D. MontesJ. C. Morales, S. Reffert, S. Sadegi, W. Seifert, D. Shulyak

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Abstract

Context. Previous simulations predicted the activity-induced radial-velocity (RV) variations of M dwarfs to range from ∼1 cm s^-1 to ∼1 km s^-1, depending on various stellar and activity parameters. Aims. We investigate the observed relations between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing CARMENES high-resolution visual-channel spectra (0.5-1μm), which were taken within the CARMENES RV planet survey during its first 20 months of operation. Methods. During this time, 287 of the CARMENES-sample stars were observed at least five times. From each spectrum we derived a relative RV and a measure of chromospheric Hα emission. In addition, we estimated the chromatic index (CRX) of each spectrum, which is a measure of the RV wavelength dependence. Results. Despite having a median number of only 11 measurements per star, we show that the RV variations of the stars with RV scatter of >10 m s^-1 and a projected rotation velocity v sin i > 2 km s^-1 are caused mainly by activity. We name these stars "active RV-loud stars" and find their occurrence to increase with spectral type: from ∼3% for early-type M dwarfs (M0.0-2.5 V) through ∼30% for mid-type M dwarfs (M3.0-5.5 V) to >50% for late-type M dwarfs (M6.0-9.0 V). Their RV-scatter amplitude is found to be correlated mainly with v sin i. For about half of the stars, we also find a linear RV-CRX anticorrelation, which indicates that their activity-induced RV scatter is lower at longer wavelengths. For most of them we can exclude a linear correlation between RV and Hα emission. Conclusions. Our results are in agreement with simulated activity-induced RV variations in M dwarfs. The RV variations of most active RV-loud M dwarfs are likely to be caused by dark spots on their surfaces, which move in and out of view as the stars rotate.

Original language	English
Article number	A122
Journal	Astronomy and Astrophysics
Volume	614
DOIs	https://doi.org/10.1051/0004-6361/201732362
State	Published - 1 Jun 2018
Externally published	Yes

Keywords

Stars: activity
Stars: late-type
Stars: rotation
Techniques: radial velocities

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10.1051/0004-6361/201732362

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Tal-Or, L., Zechmeister, M., Reiners, A., Jeffers, S. V., Schöfer, P., Quirrenbach, A., Amado, P. J., Ribas, I., Caballero, J. A., Aceituno, J., Bauer, F. F., Béjar, V. J. S., Czesla, S., Dreizler, S., Fuhrmeister, B., Hatzes, A. P., Johnson, E. N., Kürster, M., Lafarga, M., ... Shulyak, D. (2018). The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra. Astronomy and Astrophysics, 614, Article A122. https://doi.org/10.1051/0004-6361/201732362

@article{cdf69bfa453249118dbb3b17a18b35ce,

title = "The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra",

abstract = "Context. Previous simulations predicted the activity-induced radial-velocity (RV) variations of M dwarfs to range from ∼1 cm s-1 to ∼1 km s-1, depending on various stellar and activity parameters. Aims. We investigate the observed relations between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing CARMENES high-resolution visual-channel spectra (0.5-1μm), which were taken within the CARMENES RV planet survey during its first 20 months of operation. Methods. During this time, 287 of the CARMENES-sample stars were observed at least five times. From each spectrum we derived a relative RV and a measure of chromospheric Hα emission. In addition, we estimated the chromatic index (CRX) of each spectrum, which is a measure of the RV wavelength dependence. Results. Despite having a median number of only 11 measurements per star, we show that the RV variations of the stars with RV scatter of >10 m s-1 and a projected rotation velocity v sin i > 2 km s-1 are caused mainly by activity. We name these stars {"}active RV-loud stars{"} and find their occurrence to increase with spectral type: from ∼3% for early-type M dwarfs (M0.0-2.5 V) through ∼30% for mid-type M dwarfs (M3.0-5.5 V) to >50% for late-type M dwarfs (M6.0-9.0 V). Their RV-scatter amplitude is found to be correlated mainly with v sin i. For about half of the stars, we also find a linear RV-CRX anticorrelation, which indicates that their activity-induced RV scatter is lower at longer wavelengths. For most of them we can exclude a linear correlation between RV and Hα emission. Conclusions. Our results are in agreement with simulated activity-induced RV variations in M dwarfs. The RV variations of most active RV-loud M dwarfs are likely to be caused by dark spots on their surfaces, which move in and out of view as the stars rotate.",

keywords = "Stars: activity, Stars: late-type, Stars: rotation, Techniques: radial velocities",

author = "L. Tal-Or and M. Zechmeister and A. Reiners and Jeffers, {S. V.} and P. Sch{\"o}fer and A. Quirrenbach and Amado, {P. J.} and I. Ribas and Caballero, {J. A.} and J. Aceituno and Bauer, {F. F.} and B{\'e}jar, {V. J.S.} and S. Czesla and S. Dreizler and B. Fuhrmeister and Hatzes, {A. P.} and Johnson, {E. N.} and M. K{\"u}rster and M. Lafarga and D. Montes and Morales, {J. C.} and S. Reffert and S. Sadegi and W. Seifert and D. Shulyak",

note = "Publisher Copyright: {\textcopyright} 2018 ESO.",

year = "2018",

month = jun,

day = "1",

doi = "10.1051/0004-6361/201732362",

language = "אנגלית",

volume = "614",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

}

Tal-Or, L, Zechmeister, M, Reiners, A, Jeffers, SV, Schöfer, P, Quirrenbach, A, Amado, PJ, Ribas, I, Caballero, JA, Aceituno, J, Bauer, FF, Béjar, VJS, Czesla, S, Dreizler, S, Fuhrmeister, B, Hatzes, AP, Johnson, EN, Kürster, M, Lafarga, M, Montes, D, Morales, JC, Reffert, S, Sadegi, S, Seifert, W & Shulyak, D 2018, 'The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra', Astronomy and Astrophysics, vol. 614, A122. https://doi.org/10.1051/0004-6361/201732362

TY - JOUR

T1 - The CARMENES search for exoplanets around M dwarfs

T2 - Radial-velocity variations of active stars in visual-channel spectra

AU - Tal-Or, L.

AU - Zechmeister, M.

AU - Reiners, A.

AU - Jeffers, S. V.

AU - Schöfer, P.

AU - Quirrenbach, A.

AU - Amado, P. J.

AU - Ribas, I.

AU - Caballero, J. A.

AU - Aceituno, J.

AU - Bauer, F. F.

AU - Béjar, V. J.S.

AU - Czesla, S.

AU - Dreizler, S.

AU - Fuhrmeister, B.

AU - Hatzes, A. P.

AU - Johnson, E. N.

AU - Kürster, M.

AU - Lafarga, M.

AU - Montes, D.

AU - Morales, J. C.

AU - Reffert, S.

AU - Sadegi, S.

AU - Seifert, W.

AU - Shulyak, D.

PY - 2018/6/1

Y1 - 2018/6/1

N2 - Context. Previous simulations predicted the activity-induced radial-velocity (RV) variations of M dwarfs to range from ∼1 cm s-1 to ∼1 km s-1, depending on various stellar and activity parameters. Aims. We investigate the observed relations between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing CARMENES high-resolution visual-channel spectra (0.5-1μm), which were taken within the CARMENES RV planet survey during its first 20 months of operation. Methods. During this time, 287 of the CARMENES-sample stars were observed at least five times. From each spectrum we derived a relative RV and a measure of chromospheric Hα emission. In addition, we estimated the chromatic index (CRX) of each spectrum, which is a measure of the RV wavelength dependence. Results. Despite having a median number of only 11 measurements per star, we show that the RV variations of the stars with RV scatter of >10 m s-1 and a projected rotation velocity v sin i > 2 km s-1 are caused mainly by activity. We name these stars "active RV-loud stars" and find their occurrence to increase with spectral type: from ∼3% for early-type M dwarfs (M0.0-2.5 V) through ∼30% for mid-type M dwarfs (M3.0-5.5 V) to >50% for late-type M dwarfs (M6.0-9.0 V). Their RV-scatter amplitude is found to be correlated mainly with v sin i. For about half of the stars, we also find a linear RV-CRX anticorrelation, which indicates that their activity-induced RV scatter is lower at longer wavelengths. For most of them we can exclude a linear correlation between RV and Hα emission. Conclusions. Our results are in agreement with simulated activity-induced RV variations in M dwarfs. The RV variations of most active RV-loud M dwarfs are likely to be caused by dark spots on their surfaces, which move in and out of view as the stars rotate.

AB - Context. Previous simulations predicted the activity-induced radial-velocity (RV) variations of M dwarfs to range from ∼1 cm s-1 to ∼1 km s-1, depending on various stellar and activity parameters. Aims. We investigate the observed relations between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing CARMENES high-resolution visual-channel spectra (0.5-1μm), which were taken within the CARMENES RV planet survey during its first 20 months of operation. Methods. During this time, 287 of the CARMENES-sample stars were observed at least five times. From each spectrum we derived a relative RV and a measure of chromospheric Hα emission. In addition, we estimated the chromatic index (CRX) of each spectrum, which is a measure of the RV wavelength dependence. Results. Despite having a median number of only 11 measurements per star, we show that the RV variations of the stars with RV scatter of >10 m s-1 and a projected rotation velocity v sin i > 2 km s-1 are caused mainly by activity. We name these stars "active RV-loud stars" and find their occurrence to increase with spectral type: from ∼3% for early-type M dwarfs (M0.0-2.5 V) through ∼30% for mid-type M dwarfs (M3.0-5.5 V) to >50% for late-type M dwarfs (M6.0-9.0 V). Their RV-scatter amplitude is found to be correlated mainly with v sin i. For about half of the stars, we also find a linear RV-CRX anticorrelation, which indicates that their activity-induced RV scatter is lower at longer wavelengths. For most of them we can exclude a linear correlation between RV and Hα emission. Conclusions. Our results are in agreement with simulated activity-induced RV variations in M dwarfs. The RV variations of most active RV-loud M dwarfs are likely to be caused by dark spots on their surfaces, which move in and out of view as the stars rotate.

KW - Stars: activity

KW - Stars: late-type

KW - Stars: rotation

KW - Techniques: radial velocities

UR - http://www.scopus.com/inward/record.url?scp=85049588036&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201732362

DO - 10.1051/0004-6361/201732362

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AN - SCOPUS:85049588036

SN - 0004-6361

VL - 614

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

M1 - A122

ER -

The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra

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