- ID:
- ivo://CDS.VizieR/J/A+A/615/A6
- Title:
- Photospheric parameters of CARMENES stars
- Short Name:
- J/A+A/615/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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. 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. We used a {chi}^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 Teff, logg, and [Fe/H] show degeneracies, the surface gravity is determined independently using stellar evolutionary models. 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 {sigma}_Teff_=51K, {sigma}_logg_=0.07, and {sigma}_[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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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/216/7
- Title:
- Planets Around Low-Mass Stars (PALMS). IV.
- Short Name:
- J/ApJS/216/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a high-contrast adaptive optics imaging search for giant planets and brown dwarfs (>~1M_Jup_) around 122 newly identified nearby (<~40pc) young M dwarfs. Half of our targets are younger than 135Myr and 90% are younger than the Hyades (620Myr). After removing 44 close stellar binaries (implying a stellar companion fraction of >35.4%+/-4.3% within 100AU), 27 of which are new or spatially resolved for the first time, our remaining sample of 78 single M dwarfs makes this the largest imaging search for planets around young low-mass stars (0.1-0.6M_{sun}_) to date. Our H- and K-band coronagraphic observations with Keck/NIRC2 and Subaru/HiCIAO achieve typical contrasts of 12-14mag and 9-13mag at 1", respectively, which correspond to limiting planet masses of 0.5-10M_Jup_ at 5-33AU for 85% of our sample. We discovered four young brown dwarf companions: 1RXS J235133.3+312720B (32+/-6M_Jup_; L0^+2^_-1_; 120+/-20AU), GJ 3629B (64^+30^_-23_M_Jup_; M7.5+/-0.5; 6.5+/-0.5AU), 1RXS J034231.8+121622B (35+/-8M_Jup_; L0+/-1; 19.8+/-0.9AU), and 2MASS J15594729+4403595B (43+/-9M_Jup_; M8.0+/-0.5; 190+/-20AU). Over 150 candidate planets were identified; we obtained follow-up imaging for 56% of these but all are consistent with background stars. Our null detection of planets enables strong statistical constraints on the occurrence rate of long-period giant planets around single M dwarfs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/407/2269
- Title:
- Polarisation of a sample of late M dwarfs
- Short Name:
- J/MNRAS/407/2269
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here the final results of the first spectropolarimetric survey of a small sample of active M dwarfs, aimed at providing observational constraints on dynamo action on both sides of the full-convection threshold (spectral type M4). Our two previous studies (Donati et al. 2008. Cat. J/MNRAS/390/545; Morin et al., 2008, Cat. J/MNRAS/384/77) were focused on early and mid M dwarfs. The present paper examines 11 fully convective late M dwarfs (spectral types M5-M8). Tomographic imaging techniques were applied to time-series of circularly polarised profiles of 6 stars, in order to infer their large-scale magnetic topologies. For 3 other stars we could not produce such magnetic maps, because of low variability of the Stokes V signatures, but were able to derive some properties of the magnetic fields. We find 2 distinct categories of magnetic topologies: on the one hand strong axisymmetric dipolar fields (similar to mid M dwarfs), and on the other hand weak fields generally featuring a significant non-axisymmetric component, and sometimes a significant toroidal one. Comparison with unsigned magnetic fluxes demonstrates that the second category of magnetic fields shows less organization (less energy in the large scales), similarly to partly convective early M dwarfs. Stars in both categories have similar stellar parameters, our data do not evidence a separation between these 2 categories in the mass-rotation plane. We also report marginal detection of a large-scale magnetic field on the M8 star VB 10 featuring a significant toroidal axisymmetric component, whereas no field is detectable on VB 8 (M7).
- ID:
- ivo://CDS.VizieR/J/ApJ/807/45
- Title:
- Potentially habitable planets orbiting M dwarfs
- Short Name:
- J/ApJ/807/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an improved estimate of the occurrence rate of small planets orbiting small stars by searching the full four-year Kepler data set for transiting planets using our own planet detection pipeline and conducting transit injection and recovery simulations to empirically measure the search completeness of our pipeline. We identified 156 planet candidates, including one object that was not previously identified as a Kepler Object of Interest. We inspected all publicly available follow-up images, observing notes, and centroid analyses, and corrected for the likelihood of false positives. We evaluated the sensitivity of our detection pipeline on a star-by-star basis by injecting 2000 transit signals into the light curve of each target star. For periods shorter than 50 days, we find 0.56^+0.06^_-0.05_ Earth-size planets (1-1.5R_{Earth}_) and 0.46^+0.07^_-0.05_ super-Earths (1.5-2R_{Earth}_) per M dwarf. In total, we estimate a cumulative planet occurrence rate of 2.5+/-0.2 planets per M dwarf with radii 1-4R_{Earth}_ and periods shorter than 200 days. Within a conservatively defined habitable zone (HZ) based on the moist greenhouse inner limit and maximum greenhouse outer limit, we estimate an occurrence rate of 0.16^+0.17^_-0.07_ Earth-size planets and 0.12^+0.10^_-0.05_ super-Earths per M dwarf HZ. Adopting the broader insolation boundaries of the recent Venus and early Mars limits yields a higher estimate of 0.24^+0.18^_-0.08_ Earth-size planets and 0.21^+0.11^_-0.06_ super-Earths per M dwarf HZ. This suggests that the nearest potentially habitable non-transiting and transiting Earth-size planets are 2.6+/-0.4pc and 10.6^+1.6^_-1.8_pc away, respectively. If we include super-Earths, these distances diminish to 2.1+/-0.2pc and 8.6^+0.7^_-0.8_pc.
- ID:
- ivo://CDS.VizieR/J/PASP/109/849
- Title:
- Probing the LHS Catalog
- Short Name:
- J/PASP/109/849
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present moderate resolution spectroscopy of 111 cool dwarf stars to supplement the observations we have already presented in the Palomar/MSU Nearby-Star Spectroscopic Survey. The sample consists of 71 suspected nearby stars added to the Preliminary Third Catalog of Nearby Stars since 1991 as well as 40 faint red stars selected from the LHS catalog. The study was aimed at identifying interesting red dwarfs, particularly new nearby, ultracool dwarfs, and very metal-poor stars. The observations were made using the Palomar 60-inch, the Hale 200-inch and the Las Campanas 100-inch telescopes between June 1995 and January 1996. The spectral resolution is approximately 3 Angstroms per pixel with wavelength coverage from 6200 to 7500 Angstroms. Table 2 contains bandstrengths for TiO, CaH, and CaOH indices.
- ID:
- ivo://CDS.VizieR/J/ApJ/789/102
- Title:
- Properties of late M-dwarfs
- Short Name:
- J/ApJ/789/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of multiplicity among low-mass stars is a key issue to understanding the formation of stars and brown dwarfs, and recent surveys have yielded large enough samples of nearby low-mass stars to study this issue statistically to good accuracy. Previously, we have presented a multiplicity study of ~700 early/mid M-type stars observed with the AstraLux high-resolution Lucky Imaging cameras. Here, we extend the study of multiplicity in M-type stars through studying 286 nearby mid/late M-type stars, bridging the gap between our previous study and multiplicity studies of brown dwarfs. Most of the targets have been observed more than once, allowing us to assess common proper motion to confirm companionship. We detect 68 confirmed or probable companions in 66 systems, of which 41 were previously undiscovered. Detections are made down to the resolution limit of ~100 mas of the instrument. The raw multiplicity in the AstraLux sensitivity range is 17.9%, leading to a total multiplicity fraction of 21%-27% depending on the mass ratio distribution, which is consistent with being flat down to mass ratios of ~0.4, but cannot be stringently constrained below this value. The semi-major axis distribution is well represented by a log-normal function with {mu}_a_= 0.78 and {sigma}_a_= 0.47, which is narrower and peaked at smaller separations than for a Sun-like sample. This is consistent with a steady decrease in average semi-major axis from the highest-mass binary stars to the brown dwarf binaries.
- ID:
- ivo://CDS.VizieR/J/AJ/151/106
- Title:
- Radial velocities in 2006-2014 for HD 89758
- Short Name:
- J/AJ/151/106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report that the spectroscopic binary {mu} Ursae Majoris ({mu} UMa) has secondary RV variations of 471.2 days in addition to those of 230.0 days already known. Keplerian orbit analysis yields stellar mass companions of 1.6M_{sun}_ for the 230 day period and 0.14M_{sun}_for the 471 day period. However, the HIPPARCOS photometries show a period similar to the stellar rotational period, which is one-quarter of the RV period. Variations in the bisector velocity curvature show a period of 463.6 days. We also find ~473 day variations in the equivalent width (EW) measurements of the H_{alpha}_ and H_{beta}_ lines, whose origin is probably stellar activity. We note that the nature of 471 day variations is similar to one observed in "Sequence D" of Asymptotic Giant Branch pulsating stars. We therefore conclude that the RV and the EW variations in the spectroscopic binary M giant {mu} UMa A originate from the complex pulsations and the chromospheric activity.
- ID:
- ivo://CDS.VizieR/J/AJ/160/3
- Title:
- Radial velocities of M-dwarf LTT 3780 with HARPS
- Short Name:
- J/AJ/160/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the confirmation of two new planets transiting the nearby mid-M dwarf LTT3780 (TIC36724087, TOI-732, V=13.07, Ks=8.204, Rs=0.374R{sun}, Ms=0.401 M{sun}, d=22pc). The two planet candidates are identified in a single Transiting Exoplanet Survey Satellite sector and validated with reconnaissance spectroscopy, ground-based photometric follow-up, and high-resolution imaging. With measured orbital periods of P_b_=0.77, P_c_=12.25days and sizes r_p,b_=1.33{+/-}0.07, r_p,c_=2.30{+/-}0.16R{earth}, the two planets span the radius valley in period-radius space around low-mass stars, thus making the system a laboratory to test competing theories of the emergence of the radius valley in that stellar mass regime. By combining 63 precise radial velocity measurements from the High Accuracy Radial velocity Planet Searcher (HARPS) and HARPS-N, we measure planet masses of m_p,b_=2.62_-0.46_^+0.48^ and m_p,c_=8.6_-1.3_^+1.6^M{earth}, which indicates that LTT3780b has a bulk composition consistent with being Earth-like, while LTT3780c likely hosts an extended H/He envelope. We show that the recovered planetary masses are consistent with predictions from both photoevaporation and core-powered mass-loss models. The brightness and small size of LTT3780, along with the measured planetary parameters, render LTT3780b and c as accessible targets for atmospheric characterization of planets within the same planetary system and spanning the radius valley.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/29
- Title:
- Radial velocities of TOI-1728 with HPF
- Short Name:
- J/ApJ/899/29
- Date:
- 14 Mar 2022 09:03:00
- Publisher:
- CDS
- Description:
- We confirm the planetary nature of TOI-1728b using a combination of ground-based photometry, near-infrared Doppler velocimetry and spectroscopy with the Habitable-zone Planet Finder. TOI-1728 is an old, inactive M0 star with Teff=3980_-32_^+31^K, which hosts a transiting super-Neptune at an orbital period of ~3.49days. Joint fitting of the radial velocities and TESS and ground-based transits yields a planetary radius of 5.05_-0.17_^+0.16^ R{Earth}, mass 26.78_-5.13_^+5.43^M{Earth}, and eccentricity 0.057_-0.039_^+0.054^. We estimate the stellar properties, and perform a search for He 10830{AA} absorption during the transit of this planet and claim a null detection with an upper limit of 1.1% with 90% confidence. A deeper level of He 10830{AA} absorption has been detected in the planet atmosphere of GJ3470b, a comparable gaseous planet. TOI-1728b is the largest super-Neptune-the intermediate subclass of planets between Neptune and the more massive gas-giant planets-discovered around an M-dwarf. With its relatively large mass and radius, TOI-1728 represents a valuable data point in the M-dwarf exoplanet mass-radius diagram, bridging the gap between the lighter Neptune-sized planets and the heavier Jovian planets known to orbit M dwarfs. With a low bulk density of 1.14_-0.24_^+0.26^g/cm^3^, and orbiting a bright host star (J~9.6, V~12.4), TOI-1728b is also a promising candidate for transmission spectroscopy both from the ground and from space, which can be used to constrain planet formation and evolutionary models.
- ID:
- ivo://CDS.VizieR/J/AJ/155/192
- Title:
- Radial velocities & photometry of AD Leonis & GJ 674
- Short Name:
- J/AJ/155/192
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- AD Leonis is a nearby magnetically active M dwarf. We find Doppler variability with a period of 2.23 days, as well as photometric signals: (1) a short-period signal, which is similar to the radial velocity signal, albeit with considerable variability; and (2) a long-term activity cycle of 4070+/-120 days. We examine the short-term photometric signal in the available All-Sky Automated Survey and Microvariability and Oscillations of STars (MOST) photometry and find that the signal is not consistently present and varies considerably as a function of time. This signal undergoes a phase change of roughly 0.8 rad when considering the first and second halves of the MOST data set, which are separated in median time by 3.38 days. In contrast, the Doppler signal is stable in the combined High-Accuracy Radial velocity Planet Searcher and High Resolution Echelle Spectrometer radial velocities for over 4700 days and does not appear to vary in time in amplitude, phase, period, or as a function of extracted wavelength. We consider a variety of starspot scenarios and find it challenging to simultaneously explain the rapidly varying photometric signal and the stable radial velocity signal as being caused by starspots corotating on the stellar surface. This suggests that the origin of the Doppler periodicity might be the gravitational tug of a planet orbiting the star in spin-orbit resonance. For such a scenario and no spin-orbit misalignment, the measured vsini indicates an inclination angle of 15.5+/-2.5{deg} and a planetary companion mass of 0.237+/-0.047 M_Jup_.
