- ID:
- ivo://CDS.VizieR/J/AJ/143/134
- Title:
- Candidate members of {beta} Pic / AB Dor groups
- Short Name:
- J/AJ/143/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present moderate resolution (R~3575) optical spectra of 19 known or suspected members of the AB Doradus and {beta} Pictoris Moving Groups, obtained with the DeVeny Spectrograph on the 72inch Perkins telescope at Lowell Observatory. For four of five recently proposed members, signatures of youth such as LiI 6708{AA} absorption and H{alpha} emission further strengthen the case for youth and membership. The lack of detected lithium in the proposed {beta} Pic member TYC 2211-1309-1 implies that it is older than all other K-type members and weakens the case for membership. Effective temperatures are determined via line ratio analyses for the 11 F, G, and early-K stars observed, and via spectral comparisons for the eight late-K and M stars observed. We assemble updated candidate membership lists for these moving groups that account for known binarity. Currently, the AB Dor Moving Group contains 127 proposed members and the {beta} Pic Moving Group holds 77 proposed members. We then use temperature, luminosity, and distance estimates to predict angular diameters for these stars; the motivation is to identify stars that can be spatially resolved with long-baseline optical/infrared interferometers in order to improve age estimates for these groups and to constrain evolutionary models at young ages. Considering the portion of the sky accessible to northern hemisphere facilities (DE>-30), six stars have diameters large enough to be spatially resolved ({theta}>0.4mas) with the CHARA Array, which currently has the world's longest baseline of 331m; this subsample includes the low-mass M2.5 member of AB Dor, GJ 393, which is likely to still be pre-main sequence. For southern hemisphere facilities (DE<+30), 18 stars have diameters larger than this limiting size, including the low-mass debris disk star AU Mic (0.72mas). However, the longest baselines of southern hemisphere interferometers (160m) are only able to resolve the largest of these, the B6 star {alpha} Gru (1.17mas); proposed long-baseline stations may alleviate the current limitations.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/3133
- Title:
- Candidate Neptunes around late-type dwarfs
- Short Name:
- J/MNRAS/437/3133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Studies of transiting Neptune-size planets orbiting close to nearby bright stars can inform theories of planet formation because mass and radius and therefore mean density can be accurately estimated and compared with interior models. The distribution of such planets with stellar mass and orbital period relative to their Jovian-mass counterparts can test scenarios of orbital migration, and whether "hot" (period <10d) Neptunes evolved from "hot" Jupiters as a result of mass loss. We searched 1763 late K and early M dwarf stars for transiting Neptunes by analyzing photometry from the Wide Angle Search for Planets and obtaining high-precision (<=10^-3^) follow-up photometry of stars with candidate transit signals. We identified 92 candidate signals among 80 other stars and carried out 148 observations of predicted candidate transits with 1-2m telescopes.
- ID:
- ivo://CDS.VizieR/J/ApJ/770/90
- Title:
- Candidate planets in the habitable zones
- Short Name:
- J/ApJ/770/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A key goal of the Kepler mission is the discovery of Earth-size transiting planets in "habitable zones" where stellar irradiance maintains a temperate climate on an Earth-like planet. Robust estimates of planet radius and irradiance require accurate stellar parameters, but most Kepler systems are faint, making spectroscopy difficult and prioritization of targets desirable. The parameters of 2035 host stars were estimated by Bayesian analysis and the probabilities p_HZ_ that 2738 candidate or confirmed planets orbit in the habitable zone were calculated. Dartmouth Stellar Evolution Program models were compared to photometry from the Kepler Input Catalog, priors for stellar mass, age, metallicity and distance, and planet transit duration. The analysis yielded probability density functions for calculating confidence intervals of planet radius and stellar irradiance, as well as p_HZ_. Sixty-two planets have p_HZ_>0.5 and a most probable stellar irradiance within habitable zone limits. Fourteen of these have radii less than twice the Earth; the objects most resembling Earth in terms of radius and irradiance are KOIs 2626.01 and 3010.01, which orbit late K/M-type dwarf stars. The fraction of Kepler dwarf stars with Earth-size planets in the habitable zone ({eta}_{Earth}_) is 0.46, with a 95% confidence interval of 0.31-0.64. Parallaxes from the Gaia mission will reduce uncertainties by more than a factor of five and permit definitive assignments of transiting planets to the habitable zones of Kepler stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/778/132
- Title:
- C and O abundances in 55 Cnc
- Short Name:
- J/ApJ/778/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The super-Earth exoplanet 55 Cnc e, the smallest member of a five-planet system, has recently been observed to transit its host star. The radius estimates from transit observations, coupled with spectroscopic determinations of mass, provide constraints on its interior composition. The composition of exoplanetary interiors and atmospheres are particularly sensitive to elemental C/O ratio, which to first order can be estimated from the host stars. Results from a recent spectroscopic study analyzing the 6300{AA}[OI] line and two CI lines suggest that 55 Cnc has a carbon-rich composition (C/O=1.12+/-0.09). However, oxygen abundances derived using the 6300{AA}[OI] line are highly sensitive to a Ni I blend, particularly in metal-rich stars such as 55 Cnc ([Fe/H]=0.34+/-0.18). Here, we further investigate 55 Cnc's composition by deriving the carbon and oxygen abundances from these and additional C and O absorption features. We find that the measured C/O ratio depends on the oxygen lines used. The C/O ratio that we derive based on the 6300{AA}[OI] line alone is consistent with the previous value. Yet, our investigation of additional abundance indicators results in a mean C/O ratio of 0.78+/-0.08. The lower C/O ratio of 55 Cnc determined here may place this system at the sensitive boundary between protoplanetary disk compositions giving rise to planets with high (>0.8) versus low (<0.8) C/O ratios. This study illustrates the caution that must applied when determining planet host star C/O ratios, particularly in cool, metal-rich stars.
- ID:
- ivo://CDS.VizieR/J/A+A/597/A47
- Title:
- CARMENES input catalogue of M dwarfs II
- Short Name:
- J/A+A/597/A47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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. 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 M_J_-spectral type and mass-M_I_ 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.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A76
- Title:
- CARMENES input catalogue of M dwarfs. III.
- Short Name:
- J/A+A/614/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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{alpha} 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{alpha} inactive with low rotational velocities and that late-M dwarfs are H{alpha} 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.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A126
- Title:
- CARMENES input catalogue of M dwarfs. IV.
- Short Name:
- J/A+A/621/A126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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. 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, obtained by us with four 0.2-0.8m telescopes at high geographical latitudes. We present 142 rotation periods (73 new) from 0.12d to 133d and ten long-term activity cycles (six new) from 3.0a to 11.5a. We compare our determinations with those in the existing literature, investigate the distribution of Prot in the CARMENES input catalogue, the amplitude of photometric variability, and their relation to vsini and pEW(H{alpha}), and identify three very active stars with new rotation periods between 0.34d and 23.6d.
- ID:
- ivo://CDS.VizieR/J/A+A/609/A117
- Title:
- CARMENES radial velocity curves of 7 M-dwarf
- Short Name:
- J/A+A/609/A117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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. 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 are 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 11.4days. Although we cannot confirm the super-Earth planet GJ 15 Ab, we show evidence for a possible long-period (Pc=7025^+972^_-629_days) Saturn-mass (m_c_sini=51.8^+5.5^_-5.8_M_{Earth}_) 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 Pc=532.6^+4.2^_-2.5_days, eccentricity e_c_=0.342^+0.050^_-0.062_ and minimum mass m_c_sini=68.1^+4.9^_-2.2_M_{Earth}_. 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.
- ID:
- ivo://CDS.VizieR/J/A+A/652/A116
- Title:
- CARMENES time-resolved CaII H&K catalog
- Short Name:
- J/A+A/652/A116
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Radial-velocity (RV) jitter caused by stellar magnetic activity is an important factor in state-of-the-art exoplanet discovery surveys such as CARMENES. Stellar rotation, along with heterogeneities in the photosphere and chromosphere caused by activity, can result in false-positive planet detections. Hence, it is necessary to determine the stellar rotation period and compare it to any putative planetary RV signature. Long-term measurements of activity indicators such as the chromospheric emission in the CaII H&K lines enable the identification of magnetic activity cycles. In order to determine stellar rotation periods and study the long-term behavior of magnetic activity of the CARMENES guaranteed time observations (GTO) sample, it is advantageous to extract R'HK time series from archival data, since the CARMENES spectrograph does not cover the blue range of the stellar spectrum containing the Ca II H&K lines. We have assembled a catalog of 11634 archival spectra of 186 M dwarfs acquired by seven different instruments covering the CaII H&K regime: ESPADONS, FEROS, HARPS, HIRES, NARVAL, TIGRE, and UVES. The relative chromospheric flux in these lines, R'HK, was directly extracted from the spectra by rectification with PHOENIX synthetic spectra via narrow passbands around the Ca II H&K line cores. The combination of archival spectra from various instruments results in time series for 186 stars from the CARMENES GTO sample. As an example of the use of the catalog, we report the tentative discovery of three previously unknown activity cycles of M dwarfs. We conclude that the method of extracting R'HK with the use of model spectra yields consistent results for different instruments and that the compilation of this catalog will enable the analysis of long-term activity time series for a large number of M dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A112
- Title:
- CARMENES VIS RVs of 3 M dwarfs
- Short Name:
- J/A+A/643/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We announce the discovery of two planets orbiting the M dwarfs GJ 251 (0.360+/-0.015M_{sun}_) and HD 238090 (0.578+/-0.021M_{sun}_) based on CARMENES radial velocity (RV) data. In addition, we independently confirm with CARMENES data the existence of Lalande 21185 b, a planet that has recently been discovered with the SOPHIE spectrograph. All three planets belong to the class of warm or temperate super-Earths and share similar properties. The orbital periods are 14.24d, 13.67d, and 12.95d and the minimum masses are 4.0+/-0.4M_{sun}_, 6.9+/-0.9M_{sun}_, and 2.7+/-0.3M_{sun}_ for GJ 251 b, HD 238090 b, and Lalande 21185 b, respectively. Based on the orbital and stellar properties, we estimate equilibrium temperatures of 351.0+/-1.4K for GJ 251 b, 469.6+/-2.6K for HD 238090 b, and 370.1+/-6.8K for Lalande 21185 b. For the latter we resolve the daily aliases that were present in the SOPHIE data and that hindered an unambiguous determination of the orbital period. We find no significant signals in any of our spectral activity indicators at the planetary periods. The RV observations were accompanied by contemporaneous photometric observations. We derive stellar rotation periods of 122.1+/-2.2d and 96.7+/-3.7d for GJ 251 and HD 238090, respectively. The RV data of all three stars exhibit significant signals at the rotational period or its first harmonic. For GJ 251 and Lalande 21185, we also find long-period signals around 600d, and 2900d, respectively, which we tentatively attribute to long-term magnetic cycles. We apply a Bayesian approach to carefully model the Keplerian signals simultaneously with the stellar activity using Gaussian process regression models and extensively search for additional significant planetary signals hidden behind the stellar activity. Current planet formation theories suggest that the three systems represent a common architecture, consistent with formation following the core accretion paradigm.
