CARMENES input catalogue of M dwarfs Cortés-Contreras, M.; Béjar, V. J. S.; Caballero, J. A. ...
Astronomy and astrophysics (Berlin),
2016, 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 1.5 m Telescopio Carlos Sánchez 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-spectral 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 14 pc. 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 ± 2.0%. The bias-corrected multiplicity fraction in our volume-limited sample is 19.5 ± 2.3% for angular separations of 0.2 to 5.0 arcsec (1.4−65.6 au), with a peak in the distribution of the projected physical separations at 2.5−7.5 au. For M0.0-M3.5 V 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 50 au also tend to be of equal mass. For 26 of our systems, we estimated orbital periods shorter than 50 a, 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 0.2 arcsec, longer than 5.0 arcsec, 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 main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS ...and either were reported to have one short period planetary companion (GJ 15 A, GJ 176, GJ 436, GJ 536 and GJ 1148) or are multiple planetary systems (GJ 581 and GJ 876).
Aims.
We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES.
Methods.
We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems were fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability.
Results.
We confirm or provide supportive arguments for planets around all the investigated stars except for GJ 15 A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ 15 Ab, we show evidence for a possible long-period (
P
c
= 7030
-630
+970
d) Saturn-mass (
m
c
sin
i
= 51.8
-5.8
+5.5
M
⊕
) planet around GJ 15 A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ 1148, for which we estimate a period
P
c
= 532.6
-2.5
+4.1
days, eccentricity
e
c
= 0.342
-0.062
+0.050
and minimum mass
m
c
sin
i
= 68.1
-2.2
+4.9
M
⊕
.
Conclusions.
The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars.
Dynamical histories of planetary systems, as well as the atmospheric evolution of highly irradiated planets, can be studied by characterizing the ultra-short-period planet population, which the TESS ...mission is particularly well suited to discover. Here, we report on the follow-up of a transit signal detected in the TESS sector 19 photometric time series of the M3.0 V star TOI-1685 (2MASS J04342248+4302148). We confirm the planetary nature of the transit signal, which has a period of
P
b
= 0.6691403
−0.0000021
+0.0000023
d, using precise radial velocity measurements taken with the CARMENES spectrograph. From the joint photometry and radial velocity analysis, we estimate the following parameters for TOI-1685 b: a mass of
M
b
= 3.78
−0.63
+0.63
M
⊕
, a radius of
R
b
= 1.70
−0.07
+0.07
R
⊕
, which together result in a bulk density of
ρ
b
= 4.21
−0.82
+0.95
g cm
−3
, and an equilibrium temperature of
T
eq
= 1069
−16
+16
K. TOI-1685 b is the least dense ultra-short-period planet around an M dwarf known to date. TOI-1685 b is also one of the hottest transiting super-Earth planets with accurate dynamical mass measurements, which makes it a particularly attractive target for thermal emission spectroscopy. Additionally, we report with moderate evidence an additional non-transiting planet candidate in the system, TOI-1685 c, which has an orbital period of
P
c
= 9.02
−0.12
+0.10
d.
The hydrogen Paschen lines are known activity indicators, but studies of them in M~dwarfs during quiescence are as rare as their reports in flare studies. This situation is mostly caused by a lack of ...observations, owing to their location in the near-infrared regime, which is covered by few high-resolution spectrographs. We study the Pa\(\beta\) line, using a sample of 360 M~dwarfs observed by the CARMENES spectrograph. Descending the spectral sequence of inactive M~stars in quiescence, we find the Pa\(\beta\) line to get shallower until about spectral type M3.5 V, after which a slight re-deepening is observed. Looking at the whole sample, for stars with H\(\alpha\) in absorption, we find a loose anti-correlation between the (median) pseudo-equivalent widths (pEWs) of H\(\alpha\) and Pa\(\beta\) for stars of similar effective temperature. Looking instead at time series of individual stars, we often find correlation between pEW(H\(\alpha\)) and pEW(Pa\(\beta\)) for stars with H\(\alpha\) in emission and an anti-correlation for stars with H\(\alpha\) in absorption. Regarding flaring activity, we report the automatic detection of 35 Paschen line flares in 20 stars. Additionally we found visually six faint Paschen line flares in these stars plus 16 faint Paschen line flares in another 12 stars. In strong flares, Paschen lines can be observed up to Pa 14. Moreover, we find that Paschen line emission is almost always coupled to symmetric H\(\alpha\) line broadening, which we ascribe to Stark broadening, indicating high pressure in the chromosphere. Finally we report a few Pa\(\beta\) line asymmetries for flares that also exhibit strong H\(\alpha\) line asymmetries.
We report the confirmation and mass determination of a mini-Neptune transiting the M3.5 V star TOI-4438 (G 182-34) every 7.44 days. A transit signal was detected with NASA's TESS space mission in the ...sectors 40, 52, and 53. In order to validate the planet TOI-4438 b and to determine the system properties, we combined TESS data with high-precision radial velocity measurements from the CARMENES spectrograph, spanning almost one year, and ground-based transit photometry. We found that TOI-4438 b has a radius of Rb = 2.52 +/- 0.13 R_Earth (5% precision), which together with a mass of Mb=5.4 +/- 1.1 M_Earth (20% precision), results in a bulk density of rho = 1.85+0.51-0.44 g cm-3 (28% precision), aligning the discovery with a volatile-rich planet. Our interior structure retrieval with a pure water envelope yields a minimum water mass fraction of 46% (1-sigma). TOI-4438 b is a volatile-rich mini-Neptune with likely H/He mixed with molecules, such as water, CO_2, and CH_4. The primary star has a J-band magnitude of 9.7, and the planet has a high transmission spectroscopy metric (TSM) of 136 +/- 13. Taking into account the relatively warm equilibrium temperature of T_eq = 435 +/- 15 K, and the low activity level of its host star, TOI-4438 b is one of the most promising mini-Neptunes around an M dwarf for transmission spectroscopy studies.
Radial velocities (RVs) measured from high-resolution stellar spectra are routinely used to detect and characterise orbiting exoplanet companions. The different lines present in stellar spectra are ...created by several species, which are non-uniformly affected by stellar variability features such as spots or faculae. Stellar variability distorts the shape of the spectral absorption lines from which precise RVs are measured, posing one of the main problems in the study of exoplanets. In this work we aim to study how the spectral lines present in M dwarfs are independently impacted by stellar activity. We used CARMENES optical spectra of six active early- and mid-type M dwarfs to compute line-by-line RVs and study their correlation with several well-studied proxies of stellar activity. We are able to classify spectral lines based on their sensitivity to activity in five M dwarfs displaying high levels of stellar activity. We further used this line classification to compute RVs with activity-sensitive lines and less sensitive lines, enhancing or mitigating stellar activity effects in the RV time series. For specific sets of the least activity-sensitive lines, the RV scatter decreases by ~ 2 to 5 times the initial one, depending on the star. Finally, we compare these lines in the different stars analysed, finding the sensitivity to activity to vary from star to star. Despite the high density of lines and blends present in M dwarf stellar spectra, we find that a line-by-line approach is able to deliver precise RVs. Line-by-line RVs are also sensitive to stellar activity effects, and they allow for an accurate selection of activity-insensitive lines to mitigate activity effects in RV. However, we find stellar activity effects to vary in the same insensitive lines from star to star.
Planets with orbital periods shorter than 1 day are rare and have formation histories that are not completely understood. Small (\(R_\mathrm{p} < 2\; R_\oplus\)) ultra-short-period (USP) planets are ...highly irradiated, probably have rocky compositions with high bulk densities, and are often found in multi-planet systems. Additionally, USP planets found around small stars are excellent candidates for characterization using present-day instrumentation. Of the current full sample of approximately 5500 confirmed exoplanets, only 130 are USP planets and around 40 have mass and radius measurements. Wolf 327 (TOI-5747) is an M dwarf (\(R_\star = 0.406 \pm 0.015 \; R_\odot\), \(M_\star = 0.405 \pm 0.019 \; M_\odot\), \(T_{\mathrm{eff}}=3542 \pm 70\) K, and \(V = 13\) mag) located at a distance \(d = 28.5\) pc. NASA's planet hunter satellite, TESS, detected transits in this star with a period of 0.573 d (13.7 h) and with a transit depth of 818 ppm. Ground-based follow-up photometry, high resolution imaging, and radial velocity (RV) measurements taken with the CARMENES spectrograph confirm the presence of this new USP planet. Wolf 327b is a super-Earth with a radius of \(R_\mathrm{p} = 1.24 \pm 0.06 \; R_\oplus\) and a mass of \(M_\mathrm{p} = 2.53 \pm 0.46 \; M_\oplus\), yielding a bulk density of \(7.24 \pm 1.66 \)\,g cm\(^{-3}\) and thus suggesting a rocky composition. Owing to its close proximity to its host star (\(a = 0.01\) au), Wolf 327b has an equilibrium temperature of \(996 \pm 22\) K. This planet has a mass and radius similar to K2-229b, a planet with an inferred Mercury-like internal composition. Planet interior models suggest that Wolf 327b has a large iron core, a small rocky mantle, and a negligible (if any) H/He atmosphere.
We present the discovery of an Earth-mass planet (\(M_b\sin i = 1.26\pm0.21M_\oplus\)) on a 15.6d orbit of a relatively nearby (\(d\sim\)9.6pc) and low-mass (\(0.167\pm0.011 M_\odot\)) M5.0V star, ...Wolf 1069. Sitting at a separation of \(0.0672\pm0.0014\)au away from the host star puts Wolf 1069b in the habitable zone (HZ), receiving an incident flux of \(S=0.652\pm0.029S_\oplus\). The planetary signal was detected using telluric-corrected radial-velocity (RV) data from the CARMENES spectrograph, amounting to a total of 262 spectroscopic observations covering almost four years. There are additional long-period signals in the RVs, one of which we attribute to the stellar rotation period. This is possible thanks to our photometric analysis including new, well-sampled monitoring campaigns undergone with the OSN and TJO facilities that supplement archival photometry (i.e., from MEarth and SuperWASP), and this yielded an updated rotational period range of \(P_{rot}=150-170\)d, with a likely value at \(169.3^{+3.7}_{-3.6}\)d. The stellar activity indicators provided by the CARMENES spectra likewise demonstrate evidence for the slow rotation period, though not as accurately due to possible factors such as signal aliasing or spot evolution. Our detectability limits indicate that additional planets more massive than one Earth mass with orbital periods of less than 10 days can be ruled out, suggesting that perhaps Wolf 1069 b had a violent formation history. This planet is also the 6th closest Earth-mass planet situated in the conservative HZ, after Proxima Centauri b, GJ 1061d, Teegarden's Star c, and GJ 1002 b and c. Despite not transiting, Wolf 1069b is nonetheless a very promising target for future three-dimensional climate models to investigate various habitability cases as well as for sub-ms\(^{-1}\) RV campaigns to search for potential inner sub-Earth-mass planets in order to test planet formation theories.
Context: A challenge with radial-velocity (RV) data is disentangling the origin of signals either due to a planetary companion or to stellar activity. In fact, the existence of a planetary companion ...has been proposed, as well as contested, around the relatively bright, nearby M3.0V star AD Leo at the same period as the stellar rotation of 2.23d. Aims: We further investigate the nature of this signal. We introduce new CARMENES optical and near-IR RV data and an analysis in combination with archival data taken by HIRES and HARPS, along with more recent data from HARPS-N, GIANO-B, and HPF. Also, we address the confusion concerning the binarity of AD Leo. Methods: We consider possible correlations between the RVs and various stellar activity indicators accessible with CARMENES. We applied models within a Bayesian framework to determine whether a Keplerian model, a red-noise quasi-periodic model using a Gaussian process, or a mixed model would explain the observed data best. We also exclusively focus on spectral lines potentially associated with stellar activity. Results: The CARMENES RV data agree with the previously reported periodicity of 2.23d, correlate with some activity indicators, and exhibit chromaticity. However, when considering the entire RV data set, we find that a mixed model composed of a stable and a variable component performs best. Moreover, when recomputing the RVs using only spectral lines insensitive to activity, there appears to be some residual power at the period of interest. We therefore conclude that it is not possible to determinedly prove that there is no planet orbiting in synchronization with the stellar rotation given our data, current tools, machinery, and knowledge of how stellar activity affects RVs. We do rule out planets more massive than 27M_E (=0.084M_J). We also exclude any binary companion around AD Leo with Msini > 3-6M_J on orbital periods <14yr.
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