Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System

Abstract We present updated radial-velocity (RV) analyses of the AU Mic system. AU Mic is a young (22 Myr) early-M dwarf known to host two transiting planets—P b ∼ 8.46 days, R b = 4.38 − 0.18 + 0.18 R ⊕ , P c ∼ 18.86 days, R c = 3.51 − 0.16 + 0.16 R ⊕ . With visible RVs from Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical echelle Spectrographs (CARMENES)-VIS, CHIRON, HARPS, HIRES, Minerva-Australis, and Tillinghast Reflector Echelle Spectrograph, as well as near-infrared (NIR) RVs from CARMENES-NIR, CSHELL, IRD, iSHELL, NIRSPEC, and SPIRou, we provide a 5σ upper limit to the mass of AU Mic c of M c ≤ 20.13 M ⊕ and present a refined mass of AU Mic b of M b = 20.12 − 1.57 + 1.72 M ⊕ . Used in our analyses is a new RV modeling toolkit to exploit the wavelength dependence of stellar activity present in our RVs via wavelength-dependent Gaussian processes. By obtaining near-simultaneous visible and near-infrared RVs, we also compute the temporal evolution of RV “color” and introduce a regressional method to aid in isolating Keplerian from stellar activity signals when modeling RVs in future works. Using a multiwavelength Gaussian process model, we demonstrate the ability to recover injected planets at 5σ significance with semi-amplitudes down to ≈10 m s−1 with a known ephemeris, more than an order of magnitude below the stellar activity amplitude. However, we find that the accuracy of the recovered semi-amplitudes is ∼50% for such signals with our model.

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Stellar Variabilities: Challenges for the Detection and Characterization of Exoplanets

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313013227 ◽

2012 ◽

Vol 8 (S293) ◽

pp. 388-392

Author(s):

I. Boisse ◽

X. Dumusque ◽

N. C. Santos ◽

M. Oshagh ◽

X. Bonfils ◽

...

Keyword(s):

Near Infrared ◽

Parameters Estimation ◽

Habitable Zone ◽

M Dwarfs ◽

Stellar Activity ◽

Stellar Pulsation ◽

Low Mass ◽

Magnetic Cycles ◽

M Dwarf

AbstractThe photometric and RV techniques, although extremely efficient to detect and characterize planets, are, however, indirect techniques (as well as astrometry). Phenomena such as stellar pulsation, inhomogeneous convection, spots or magnetic cycles can prevent us from finding planets or they might degrade the parameters estimation. We will consider the challenges related to the knowledge of stellar activity for the next decade: detect telluric planets in the habitable zone of their stars (from G to M dwarfs), understand the activity in the low-mass end of M dwarf (on which will focus future near-infrared high-resolution spectrograph like SPIRou or CARMENES), limitation to the process of summing several transit observations (in order to characterize the atmospheric components) due to the variability of stellar activity (from the ground or with Spitzer or JWST), as well as the methods proposed and used to overcome this issue.

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The Near Infrared FeH Lines as Indicators of Surface Gravity of M stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900233597 ◽

1996 ◽

Vol 171 ◽

pp. 441-441

Author(s):

Ricardo Piorno Schiavon ◽

Beatriz Barbuy

Keyword(s):

Near Infrared ◽

Synthesis Method ◽

Population Synthesis ◽

Atmospheric Parameters ◽

M Dwarfs ◽

Synthetic Spectra ◽

Iron Hydride ◽

M Stars ◽

M Dwarf ◽

Ongoing Project

We compute synthetic spectra in the region around 1 μm, including the Wing-Ford band (WFB) of Iron Hydride (FeH) in the calculations. This band is known to be a good indicator of surface gravities of M stars. Employing Kurucz model atmospheres, we study the response of the intensity of the WFB to atmospheric parameters and check our results against observations of M dwarfs. This study is part of an ongoing project which aims to investigate the M dwarf-to-giant ratio in galaxies, through a population synthesis method, exploring a number of spectral indicators in the near infrared, such as the WFB, the NaI, CaII and CO near infrared features.

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New disk discovered with VLT/SPHERE around the M star GSC 07396−00759

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832740 ◽

2018 ◽

Vol 613 ◽

pp. L6 ◽

Cited By ~ 13

Author(s):

E. Sissa ◽

J. Olofsson ◽

A. Vigan ◽

J. C. Augereau ◽

V. D’Orazi ◽

...

Keyword(s):

Near Infrared ◽

Scattered Light ◽

Debris Disks ◽

M Dwarfs ◽

Infrared Excess ◽

Asymmetric Structures ◽

High Resolution Imagery ◽

Low Mass ◽

Dust Dynamics ◽

M Dwarf

Debris disks are usually detected through the infrared excess over the photospheric level of their host star. The most favorable stars for disk detection are those with spectral types between A and K, while the statistics for debris disks detected around low-mass M-type stars is very low, either because they are rare or because they are more difficult to detect. Terrestrial planets, on the other hand, may be common around M-type stars. Here, we report on the discovery of an extended (likely) debris disk around the M-dwarf GSC 07396−00759. The star is a wide companion of the close accreting binary V4046 Sgr. The system probably is a member of the β Pictoris Moving Group. We resolve the disk in scattered light, exploiting high-contrast, high-resolution imagery with the two near-infrared subsystems of the VLT/SPHERE instrument, operating in the Y J bands and the H2H3 doublet. The disk is clearly detected up to 1.5′′ (~110 au) from the star and appears as a ring, with an inclination i ~ 83°, and a peak density position at ~70 au. The spatial extension of the disk suggests that the dust dynamics is affected by a strong stellar wind, showing similarities with the AU Mic system that has also been resolved with SPHERE. The images show faint asymmetric structures at the widest separation in the northwest side. We also set an upper limit for the presence of giant planets to 2 MJ. Finally, we note that the 2 resolved disks around M-type stars of 30 such stars observed with SPHERE are viewed close to edge-on, suggesting that a significant population of debris disks around M dwarfs could remain undetected because of an unfavorable orientation.

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The CARMENES search for exoplanets around M dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732312 ◽

2018 ◽

Vol 615 ◽

pp. A6 ◽

Cited By ~ 33

Author(s):

V. M. Passegger ◽

A. Reiners ◽

S. V. Jeffers ◽

S. Wende-von Berg ◽

P. Schöfer ◽

...

Keyword(s):

High Resolution ◽

Near Infrared ◽

Stellar Atmosphere ◽

Stellar Atmospheres ◽

Surface Gravity ◽

M Dwarfs ◽

Low Mass Stars ◽

Target Sample ◽

M Dwarf ◽

The Phoenix

Context. The new CARMENES instrument comprises two high-resolution and high-stability spectrographs that are used to search for habitable planets around M dwarfs in the visible and near-infrared regime via the Doppler technique. Aims. Characterising our target sample is important for constraining the physical properties of any planetary systems that are detected. The aim of this paper is to determine the fundamental stellar parameters of the CARMENES M-dwarf target sample from high-resolution spectra observed with CARMENES. We also include several M-dwarf spectra observed with other high-resolution spectrographs, that is CAFE, FEROS, and HRS, for completeness. Methods. We used a χ2 method to derive the stellar parameters effective temperature Teff, surface gravity logg, and metallicity [Fe/H] of the target stars by fitting the most recent version of the PHOENIX-ACES models to high-resolution spectroscopic data. These stellar atmosphere models incorporate a new equation of state to describe spectral features of low-temperature stellar atmospheres. Since Teff, logg, and [Fe/H] show degeneracies, the surface gravity is determined independently using stellar evolutionary models. Results. We derive the stellar parameters for a total of 300 stars. The fits achieve very good agreement between the PHOENIX models and observed spectra. We estimate that our method provides parameters with uncertainties of σTeff = 51 K, σlog g = 0.07, and σ[Fe/H] = 0.16, and show that atmosphere models for low-mass stars have significantly improved in the last years. Our work also provides an independent test of the new PHOENIX-ACES models, and a comparison for other methods using low-resolution spectra. In particular, our effective temperatures agree well with literature values, while metallicities determined with our method exhibit a larger spread when compared to literature results.

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The CARMENES search for exoplanets around M dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936193 ◽

2019 ◽

Vol 632 ◽

pp. A24

Author(s):

B. Fuhrmeister ◽

S. Czesla ◽

L. Hildebrandt ◽

E. Nagel ◽

J. H. M. M. Schmitt ◽

...

Keyword(s):

Near Infrared ◽

Activity Levels ◽

Line Formation ◽

M Dwarfs ◽

Complex Behaviour ◽

X Ray ◽

Solar Type ◽

M Dwarf ◽

Calar Alto ◽

Important Activity

The He I infrared (IR) triplet at 10 830 Å is an important activity indicator for the Sun and in solar-type stars, however, it has rarely been studied in relation to M dwarfs to date. In this study, we use the time-averaged spectra of 319 single stars with spectral types ranging from M0.0 V to M9.0 V obtained with the CARMENES high resolution optical and near-infrared spectrograph at Calar Alto to study the properties of the He I IR triplet lines. In quiescence, we find the triplet in absorption with a decrease of the measured pseudo equivalent width (pEW) towards later sub-types. For stars later than M5.0 V, the He I triplet becomes undetectable in our study. This dependence on effective temperature may be related to a change in chromospheric conditions along the M dwarf sequence. When an emission in the triplet is observed, we attribute it to flaring. The absence of emission during quiescence is consistent with line formation by photo-ionisation and recombination, while flare emission may be caused by collisions within dense material. The He I triplet tends to increase in depth according to increasing activity levels, ultimately becoming filled in; however, we do not find a correlation between the pEW(He IR) and X-ray properties. This behaviour may be attributed to the absence of very inactive stars (LX∕Lbol < −5.5) in our sample or to the complex behaviour with regard to increasing depth and filling in.

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THREE NEW ECLIPSING WHITE-DWARF-M-DWARF BINARIES DISCOVERED IN A SEARCH FOR TRANSITING PLANETS AROUND M-DWARFS

The Astrophysical Journal ◽

10.1088/0004-637x/757/2/133 ◽

2012 ◽

Vol 757 (2) ◽

pp. 133 ◽

Cited By ~ 35

Author(s):

Nicholas M. Law ◽

Adam L. Kraus ◽

Rachel Street ◽

Benjamin J. Fulton ◽

Lynne A. Hillenbrand ◽

...

Keyword(s):

White Dwarf ◽

M Dwarfs ◽

Transiting Planets ◽

M Dwarf

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The CARMENES search for exoplanets around M dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732054 ◽

2018 ◽

Vol 612 ◽

pp. A49 ◽

Cited By ~ 76

Author(s):

A. Reiners ◽

M. Zechmeister ◽

J. A. Caballero ◽

I. Ribas ◽

J. C. Morales ◽

...

Keyword(s):

High Resolution ◽

Wavelength Range ◽

Near Infrared ◽

Signal To Noise Ratio ◽

Rotation Velocity ◽

Atmospheric Models ◽

M Dwarfs ◽

Low Mass Stars ◽

Low Mass ◽

M Dwarf

The CARMENES radial velocity (RV) survey is observing 324 M dwarfs to search for any orbiting planets. In this paper, we present the survey sample by publishing one CARMENES spectrum for each M dwarf. These spectra cover the wavelength range 520–1710 nm at a resolution of at least R >80 000, and we measure its RV, Hα emission, and projected rotation velocity. We present an atlas of high-resolution M-dwarf spectra and compare the spectra to atmospheric models. To quantify the RV precision that can be achieved in low-mass stars over the CARMENES wavelength range, we analyze our empirical information on the RV precision from more than 6500 observations. We compare our high-resolution M-dwarf spectra to atmospheric models where we determine the spectroscopic RV information content, Q, and signal-to-noise ratio. We find that for all M-type dwarfs, the highest RV precision can be reached in the wavelength range 700–900 nm. Observations at longer wavelengths are equally precise only at the very latest spectral types (M8 and M9). We demonstrate that in this spectroscopic range, the large amount of absorption features compensates for the intrinsic faintness of an M7 star. To reach an RV precision of 1 m s−1 in very low mass M dwarfs at longer wavelengths likely requires the use of a 10 m class telescope. For spectral types M6 and earlier, the combination of a red visual and a near-infrared spectrograph is ideal to search for low-mass planets and to distinguish between planets and stellar variability. At a 4 m class telescope, an instrument like CARMENES has the potential to push the RV precision well below the typical jitter level of 3–4 m s−1.

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The CARMENES search for exoplanets around M dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037867 ◽

2020 ◽

Vol 642 ◽

pp. A173 ◽

Cited By ~ 1

Author(s):

G. Nowak ◽

R. Luque ◽

H. Parviainen ◽

E. Pallé ◽

K. Molaverdikhani ◽

...

Keyword(s):

Planetary System ◽

Outer Planet ◽

Planetary Formation ◽

Atmospheric Models ◽

M Dwarfs ◽

Ideal Object ◽

Transiting Planets ◽

Short Period ◽

Iron Abundance ◽

M Dwarf

We present the discovery and characterisation of two transiting planets observed by the Transiting Exoplanet Survey Satellite (TESS) orbiting the nearby (d⋆ ≈ 22 pc), bright (J ≈ 9 mag) M3.5 dwarf LTT 3780 (TOI–732). We confirm both planets and their association with LTT 3780 via ground-based photometry and determine their masses using precise radial velocities measured with the CARMENES spectrograph. Precise stellar parameters determined from CARMENES high-resolution spectra confirm that LTT 3780 is a mid-M dwarf with an effective temperature of Teff = 3360 ± 51 K, a surface gravity of log g⋆ = 4.81 ± 0.04 (cgs), and an iron abundance of [Fe/H] = 0.09 ± 0.16 dex, with an inferred mass of M⋆ = 0.379 ± 0.016M⊙ and a radius of R⋆ = 0.382 ± 0.012R⊙. The ultra-short-period planet LTT 3780 b (Pb = 0.77 d) with a radius of 1.35−0.06+0.06 R⊕, a mass of 2.34−0.23+0.24 M⊕, and a bulk density of 5.24−0.81+0.94 g cm−3 joins the population of Earth-size planets with rocky, terrestrial composition. The outer planet, LTT 3780 c, with an orbital period of 12.25 d, radius of 2.42−0.10+0.10 R⊕, mass of 6.29−0.61+0.63 M⊕, and mean density of 2.45−0.37+0.44 g cm−3 belongs to the population of dense sub-Neptunes. With the two planets located on opposite sides of the radius gap, this planetary system is anexcellent target for testing planetary formation, evolution, and atmospheric models. In particular, LTT 3780 c is an ideal object for atmospheric studies with the James Webb Space Telescope (JWST).

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The CARMENES search for exoplanets around M dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935534 ◽

2019 ◽

Vol 627 ◽

pp. A116 ◽

Cited By ~ 4

Author(s):

S. Lalitha ◽

D. Baroch ◽

J. C. Morales ◽

V. M. Passegger ◽

F. F. Bauer ◽

...

Keyword(s):

Near Infrared ◽

Correlated Noise ◽

Stellar Rotation ◽

M Dwarfs ◽

Stellar Activity ◽

Orbital Parameters ◽

Rotation Periods ◽

Planetary Mass ◽

Low Mass ◽

Orbital Periods

Although M dwarfs are known for high levels of stellar activity, they are ideal targets for the search of low-mass exoplanets with the radial velocity (RV) method. We report the discovery of a planetary-mass companion around LSPM J2116+0234 (M3.0 V) and confirm the existence of a planet orbiting GJ 686 (BD+18 3421; M1.0 V). The discovery of the planet around LSPM J2116+0234 is based on CARMENES RV observations in the visual and near-infrared channels. We confirm the planet orbiting around GJ 686 by analyzing the RV data spanning over two decades of observationsfrom CARMENES VIS, HARPS-N, HARPS, and HIRES. We find planetary signals at 14.44 and 15.53 d in the RV data for LSPM J2116+0234 and GJ 686, respectively. Additionally, the RV, photometric time series, and various spectroscopic indicators show hints of variations of 42 d for LSPM J2116+0234 and 37 d for GJ 686, which we attribute to the stellar rotation periods. The orbital parameters of the planets are modeled with Keplerian fits together with correlated noise from the stellar activity. A mini-Neptune with a minimum mass of 11.8 M⊕ orbits LSPM J2116+0234 producing a RV semi-amplitude of 6.19 m s−1, while a super-Earth of mass 6.6 M⊕ orbits GJ 686 and produces a RV semi-amplitude of 3.0 m s−1. Both LSPM J2116+0234 and GJ 686 have planetary companions populating the regime of exoplanets with masses lower than 15 M⊕ and orbital periods <20 d.

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