CARMENES input catalogue of M dwarfs Jeffers, S. V.; Schöfer, P.; Lamert, A. ...
Astronomy and astrophysics (Berlin),
06/2018, Volume:
614
Journal Article
Peer reviewed
Open access
CARMENES is a spectrograph for radial velocity surveys of M dwarfs with the aim of detecting Earth-mass planets orbiting in the habitable zones of their host stars. To ensure an optimal use of the ...CARMENES guaranteed time observations, in this paper we investigate the correlation of activity and rotation for approximately 2200 M dwarfs, ranging in spectral type from M0.0 V to M9.0 V. We present new high-resolution spectroscopic observations with FEROS, CAFE, and HRS of approximately 500 M dwarfs. For each new observation, we determined its radial velocity and measured its H
α
activity index and its rotation velocity. Additionally, we have multiple observations of many stars to investigate if there are any radial velocity variations due to multiplicity. The results of our survey confirm that early-M dwarfs are H
α
inactive with low rotational velocities and that late-M dwarfs are H
α
active with very high rotational velocities. The results of this high-resolution analysis comprise the most extensive catalogue of rotation and activity in M dwarfs currently available.
Aims. We look for common proper motion companions to stars of the nearby young beta Pictoris moving group. Methods. First, we compiled a list of 185 beta Pictoris members and candidate members from ...35 representative works. Next, we used the Aladin and STILTS virtual observatory tools and the PPMXL proper motion and Washington Double Star catalogues to look for companion candidates. The resulting potential companions were subjects of a dedicated astro-photometric follow-up using public data from all-sky surveys. After discarding 67 sources by proper motion and 31 by colour-magnitude diagrams, we obtained a final list of 36 common proper motion systems. The binding energy of two of them is perhaps too small to be considered physically bound. Results. Of the 36 pairs and multiple systems, eight are new, 16 have only one stellar component previously classified as a beta Pictoris member, and three have secondaries at or below the hydrogen-burning limit. Sixteen stars are reported here for the first time as moving group members. The unexpected large number of high-order multiple systems, 12 triples and two quadruples among 36 systems, may suggest a biased list of members towards close binaries or an increment of the high-order-multiple fraction for very wide systems.
CARMENES input catalogue of M dwarfs Cortes-Contreras, M; Bejar, V J S; Caballero, J A ...
Astronomy and astrophysics (Berlin),
1/2017, Volume:
597
Journal Article
Peer reviewed
Open access
Aims. We search for low-mass companions of M dwarfs and characterize their multiplicity fraction with the purpose of helping in the selection of the most appropriate targets for the CARMENES ...exoplanet survey. Methods. We obtained high-resolution images in the I band with the lucky imaging instrument FastCam at the 1.5m Telescopio Carlos Sanchez for 490 mid- to late-M dwarfs. For all the detected binaries, we measured angular separations, position angles, and magnitude differences in the I band. We also calculated the masses of each individual component and estimated orbital periods, using the available magnitude and colour relations for M dwarfs and our own MJ-spectra l type and mass-MI relations. To avoid biases in our sample selection, we built a volume-limited sample of M0.0-M5.0 dwarfs that is complete up to 86% within 14pc. Results. From the 490 observed stars, we detected 80 companions in 76 systems, of which 30 are new discoveries. Another six companion candidates require additional astrometry to confirm physical binding. The multiplicity fraction in our observed sample is 16.7+ or -2.0%. The bias-corrected multiplicity fraction in our volume-limited sample is 19.5+ or -2.3% for angular separations of 0.2 to 5.0arcsec (1.4-65.6au), with a peak in the distribution of the projected physical separations at 2.5-7.5au. For M0.0-M3.5V primaries, our search is sensitive to mass ratios higher than 0.3 and there is a higher density of pairs with mass ratios over 0.8 compared to those at lower mass ratios. Binaries with projected physical separations shorter than 50au also tend to be of equal mass. For 26 of our systems, we estimated orbital periods shorter than 50a, 10 of which are presented here for the first time. We measured variations in angular separation and position angle that are due to orbital motions in 17 of these systems. The contribution of binaries and multiples with angular separations shorter than 0.2arcsec, longer than 5.0arcsec, and of spectroscopic binaries identified from previous searches, although not complete, may increase the multiplicity fraction of M dwarfs in our volume-limited sample to at least 36%.
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
χ
2
method to derive the stellar parameters effective temperature
T
eff
, surface gravity log
g
, 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
T
eff
, log
g
, 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 σ
Teff
= 51 K,
σ
log
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.
Context.
The Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs (CARMENES) survey is searching for Earth-like planets orbiting M ...dwarfs using the radial velocity method. Studying the stellar activity of the target stars is important to avoid false planet detections and to improve our understanding of the atmospheres of late-type stars.
Aims.
In this work we present measurements of activity indicators at visible and near-infrared wavelengths for 331 M dwarfs observed with CARMENES. Our aim is to identify the activity indicators that are most sensitive and easiest to measure, and the correlations among these indicators. We also wish to characterise their variability.
Methods.
Using a spectral subtraction technique, we measured pseudo-equivalent widths of the He
I
D
3
, H
α
, He
I
λ
10833 Å, and Pa
β
lines, the Na
I
D doublet, and the Ca
II
infrared triplet, which have a chromospheric component in active M dwarfs. In addition, we measured an index of the strength of two TiO and two VO bands, which are formed in the photosphere. We also searched for periodicities in these activity indicators for all sample stars using generalised Lomb-Scargle periodograms.
Results.
We find that the most slowly rotating stars of each spectral subtype have the strongest H
α
absorption. H
α
is correlated most strongly with He
I
D
3
, whereas Na
I
D and the Ca
II
infrared triplet are also correlated with H
α
. He
I
λ
10833 Å and Pa
β
show no clear correlations with the other indicators. The TiO bands show an activity effect that does not appear in the VO bands. We find that the relative variations of H
α
and He
I
D
3
are smaller for stars with higher activity levels, while this anti-correlation is weaker for Na
I
D and the Ca
II
infrared triplet, and is absent for He
I
λ
10833 Å and Pa
β
. Periodic variation with the rotation period most commonly appears in the TiO bands, H
α
, and in the Ca
II
infrared triplet.
We present three transit observations of HD 189733 b obtained with the high-resolution spectrograph CARMENES at Calar Alto. A strong absorption signal is detected in the near-infrared He I triplet at ...10830 Å in all three transits. During mid-transit, the mean absorption level is 0.88 ± 0.04% measured in a ±10 km s−1 range at a net blueshift of − 3.5 ± 0.4 km s−1 (10829.84–10830.57 Å). The absorption signal exhibits radial velocities of + 6.5 ± 3.1 km s−1 and − 12.6 ± 1.0 km s−1 during ingress and egress, respectively; all radial velocities are measured in the planetary rest frame. We show that stellar activity related pseudo-signals interfere with the planetary atmospheric absorption signal. They could contribute as much as 80% of the observed signal and might also affect the observed radial velocity signature, but pseudo-signals are very unlikely to explain the entire signal. The observed line ratio between the two unresolved and the third line of the He I triplet is 2.8 ± 0.2, which strongly deviates from the value expected for an optically thin atmospheres. When interpreted in terms of absorption in the planetary atmosphere, this favors a compact helium atmosphere with an extent of only 0.2 planetary radii and a substantial column density on the order of 4 × 1012 cm−2. The observed radial velocities can be understood either in terms of atmospheric circulation with equatorial superrotation or as a sign of an asymmetric atmospheric component of evaporating material. We detect no clear signature of ongoing evaporation, like pre- or post-transit absorption, which could indicate material beyond the planetary Roche lobe, or radial velocities in excess of the escape velocity. These findings do not contradict planetary evaporation, but only show that the detected helium absorption in HD 189733 b does not trace the atmospheric layers that show pronounced escape signatures.
CARMENES input catalogue of M dwarfs Díez Alonso, E.; Caballero, J. A.; Montes, D. ...
Astronomy and astrophysics (Berlin),
01/2019, Volume:
621
Journal Article
Peer reviewed
Aims.
The main goal of this work is to measure rotation periods of the M-type dwarf stars being observed by the CARMENES exoplanet survey to help distinguish radial-velocity signals produced by ...magnetic activity from those produced by exoplanets. Rotation periods are also fundamental for a detailed study of the relation between activity and rotation in late-type stars.
Methods.
We look for significant periodic signals in 622 photometric time series of 337 bright, nearby M dwarfs obtained by long-time baseline, automated surveys (MEarth, ASAS, SuperWASP, NSVS, Catalina, ASAS-SN, K2, and HATNet) and for 20 stars which we obtained with four 0.2–0.8 m telescopes at high geographical latitudes.
Results.
We present 142 rotation periods (73 new) from 0.12 d to 133 d and ten long-term activity cycles (six new) from 3.0 a to 11.5 a. We compare our determinations with those in the existing literature; we investigate the distribution of
P
rot
in the CARMENES input catalogue, the amplitude of photometric variability, and their relation to
v
sin
i
and pEW(H
α
); and we identify three very active stars with new rotation periods between 0.34 d and 23.6 d.
We present precise photospheric parameters of 282 M dwarfs determined from fitting the most recent version of PHOENIX models to high-resolution CARMENES spectra in the visible (0.52–0.96
μ
m) and NIR ...wavelength range (0.96–1.71
μ
m). With its aim to search for habitable planets around M dwarfs, several planets of different masses have been detected. The characterization of the target sample is important for the ability to derive and constrain the physical properties of any planetary systems that are detected. As a continuation of previous work in this context, we derived the fundamental stellar parameters effective temperature, surface gravity, and metallicity of the CARMENES M-dwarf targets from PHOENIX model fits using a
χ
2
method. We calculated updated PHOENIX stellar atmosphere models that include a new equation of state to especially account for spectral features of low-temperature stellar atmospheres as well as new atomic and molecular line lists. We show the importance of selecting magnetically insensitive lines for fitting to avoid effects of stellar activity in the line profiles. For the first time, we directly compare stellar parameters derived from multiwavelength range spectra, simultaneously observed for the same star. In comparison with literature values we show that fundamental parameters derived from visible spectra and visible and NIR spectra combined are in better agreement than those derived from the same spectra in the NIR alone.
Context.
For years, the standard procedure to measure radial velocities (RVs) of spectral observations consisted in cross-correlating the spectra with a binary mask, that is, a simple stellar ...template that contains information on the position and strength of stellar absorption lines. The cross-correlation function (CCF) profiles also provide several indicators of stellar activity.
Aims.
We present a methodology to first build weighted binary masks and, second, to compute the CCF of spectral observations with these masks from which we derive radial velocities and activity indicators. These methods are implemented in a python code that is publicly available.
Methods.
To build the masks, we selected a large number of sharp absorption lines based on the profile of the minima present in high signal-to-noise ratio (S/N) spectrum templates built from observations of reference stars. We computed the CCFs of observed spectra and derived RVs and the following three standard activity indicators: full-width-at-half-maximum as well as contrast and bisector inverse slope.
Results.
We applied our methodology to CARMENES high-resolution spectra and obtain RV and activity indicator time series of more than 300 M dwarf stars observed for the main CARMENES survey. Compared with the standard CARMENES template matching pipeline, in general we obtain more precise RVs in the cases where the template used in the standard pipeline did not have enough S/N. We also show the behaviour of the three activity indicators for the active star YZ CMi and estimate the absolute RV of the M dwarfs analysed using the CCF RVs.
Aims.
The aim of the project is to identify wide common proper motion companions to a sample of spectroscopically confirmed M and L metal-poor dwarfs (also known as subdwarfs) to investigate the ...impact of metallicity on the binary fraction of low-mass metal-poor binaries and to improve the determination of their metallicity from the higher-mass binary.
Methods.
We made use of Virtual Observatory tools and large-scale public surveys to look in
Gaia
for common proper motion companions to a well-defined sample of ultracool subdwarfs with spectral types later than M5 and metallicities below or equal to −0.5 dex. We collected low-resolution optical spectroscopy for our best system, which is a binary composed of one sdM1.5 subdwarf and one sdM5.5 subdwarf located at ∼1360 au, and for another two likely systems separated by more than 115 000 au.
Results.
We confirm one wide companion to an M subdwarf, and infer a multiplicity for M subdwarfs (sdMs) of 1.0
−1.0
+2.0
% for projected physical separations of up to 743 000 au. We also find four M–L systems, three of which are new detections. No colder companion was identified in any of the 219 M and L subdwarfs of the sample, mainly because of limitations on the detection of faint sources with
Gaia
. We infer a frequency of wide systems for sdM5–9.5 of 0.60
−0.60
+1.17
% for projected physical separations larger than 1 360 au (up to 142 400 au). This study shows a multiplicity rate of 1.0
−1.0
+2.0
% in sdMs, and 1.9
−1.9
+3.7
% in extreme M subdwarfs. We did not find any companion for the ultra M subdwarfs of our sample, establishing an upper limit of 5.3% on binarity for these objects.
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