ABSTRACT
Small rocky planets, as well as larger planets that suffered extensive volatile loss, tend to be drier and have thinner atmospheres as compared to Earth. Such planets probably outnumber ...worlds better endowed with volatiles, being the most common habitable planets. For the subgroup of fast rotators following eccentric orbits, atmospheres suffer radiative forcing and their heat capacity provides a method for gauging atmospheric thickness and surface conditions. We further explore the model presented in a previous paper and apply it to real and hypothetical exoplanets in the habitable zone of various classes of stars, simulating atmospheric and orbital characteristics. For planetary eccentricities e ∼ 0.3, the forcing-induced hypothetical temperature variation would reach ∼80 K for airless planets and ∼10 K for planets with substantial atmospheres. For Kepler-186 f and Kepler-442 b, assuming e ∼ 0.1, temperature variations can reach ∼24 K. We also consider habitable exomoons in circular orbits around gas giants within the habitable zone, which suffer radiative forcing due to their epicyclic motion. We study several combinations of parameters for the characterization of planets (mass, eccentricity, and semimajor axis) and exomoons (mass, orbital radius, albedo, and atmospheric characteristics) for different stellar types. For e ∼ 0.3, exomoon temperature varies up to ∼90 K, while for ∼0.6 variations can reach ∼200 K. Such exomoons may plausibly retain their volatiles by continued volcanic activity fuelled by tidal dissipation. Although currently undetectable, such effects might be within reach of future Extremely Large Telescope-class telescopes and space missions with mid-infrared and coronagraphic capabilities.
Studies of Galactic chemical, and dynamical evolution in the solar neighborhood depend on the availability of precise atmospheric parameters (effective temperature Tsubeff , metallicity Fe/H, and ...surface gravity log g) for solar-type stars. In this work, we use an alternative method based on spectral indices to determine the atmospheric parameters of a sample of nearby FGK dwarfs and sub-giants observed by the MARVELS survey at moderate resolving power. To avoid a time-consuming manual analysis, we have developed three codes to automatically normalize the observed spectra, measure the equivalent widths of the indices, and, through a comparison of those with values calculated with predetermined calibrations, estimate the atmospheric parameters of the stars. Our approach was able to recover the parameters within 80 K for Tsubeff, 0.05 dex for Fe/H, and 0.15 dex for log g, values that are lower than or equal to the typical external uncertainties found between different high-resolution analysis. The results show that the spectral indices are a competitive tool to characterize stars with intermediate resolution spectra.
ABSTRACT
We present a spectroscopic and photometric calibration to derive effective temperatures Teff and metallicities Fe/H for M dwarfs, based on a principal component analysis (PCA) of 147 ...spectral indices measured off moderate resolution (R∼11 000), high S/N (>100) spectra in the λλ 8390–8834 region, plus the J−H colour. Internal uncertainties, estimated by the residuals, are 81 K and 0.12 dex, respectively, for Teff and Fe/H, the calibrations being valid for 3050 K < T$_\text{eff}\, \lt $ 4100 K and −0.45 < Fe/H $\lt \, +$0.50 dex. The PCA calibration is a competitive model-independent method to derive Teff and Fe/H for large samples of M dwarfs, well suited to the available database of far-red spectra. The median uncertainties are 105 K and 0.23 dex for Teff and Fe/H, respectively, estimated by Monte Carlo simulations. We compare our values to other works based on photometric and spectroscopic techniques and find median differences 75 ± 273 K and 0.02 ± 0.31 dex for Teff and Fe/H, respectively, achieving good accuracy but relatively low precision. We find considerable disagreement in the literature between atmospheric parameters for stars in common. We use the new calibration to derive Teff and Fe/H for 178 K7-M5 dwarfs, many previously unstudied. Our metallicity distribution function for nearby M dwarfs peaks at Fe/H∼−0.10 dex, in good agreement with the RAVE distribution for GK dwarfs. We present radial velocities (internal precision 1.4 km s−1) for 99 objects without previous measurements. The kinematics of the sample shows it to be fully dominated by thin/thick disc stars, excepting the well-known high-velocity Kapteyn’s star.
We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity ...Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Kepierian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695 super(+0.0188) sub(0.0187) days, an eccentricity of 0.4375 + or - 0.0040, and a semi-amplitude of 2948.14 super(+16.65) sub(-16.55) m s super(-1). Using additional high-resolution spectroscopy, we find the host star has an effective temperature T sub(eff) = 6004 + or - 34 K, a surface gravity log g (cgs) = 4.55 + or - 0.17, and a metallicity Fe/H = +0.04 + or - 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 + or - 0.09 M sub(odot) and 0.92 + or - 0.19 R sub(odot). The minimum mass of MARVELS-5b is 65.0 + or - 2.9 M sub(Jup), indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 + or - 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M sub(odot) at a separation larger than 40 AU.
In 2005 we suggested a relation between the optimal locus of gas giant planet formation, prior to migration, and the metallicity of the host star, based on the core accretion model, and radial ...profiles of dust surface density and gas temperature. At that time, less than 200 extrasolar planets were known, limiting the scope of our analysis. Here, we take into account the expanded statistics allowed by new discoveries, in order to check the validity of some premises. We compare predictions with the present available data and results for different stellar mass ranges. We find that the zero age planetary orbit (ZAPO) hypothesis continues to hold after a two order of magnitude increase in discovered planets, as well as the prediction that planets around metal poor stars would have shorter orbits.
Halite (NaCl mineral) has exhibited the potential to preserve microorganisms for millions of years on Earth. This mineral was also identified on Mars and in meteorites. In this study, we investigated ...the potential of halite crystals to protect microbial life-forms on the surface of an airless body (
., meteorite), for instance, during a lithopanspermia process (interplanetary travel step) in the early Solar System. To investigate the effect of the radiation of the young Sun on microorganisms, we performed extensive simulation experiments by employing a synchrotron facility. We focused on two exposure conditions: vacuum (low Earth orbit, 10
Pa) and vacuum-ultraviolet (VUV) radiation (range 57.6-124 nm, flux 7.14 W/m
), with the latter representing an extreme scenario with high VUV fluxes comparable to the amount of radiation of a stellar superflare from the young Sun. The stellar VUV parameters were estimated by using the very well-studied solar analog of the young Sun, κ
Cet. To evaluate the protective effects of halite, we entrapped a halophilic archaeon (
) and a non-halophilic bacterium (
) in laboratory-grown halite. Control groups were cells entrapped in salt crystals (mixtures of different salts and NaCl) and non-trapped (naked) cells, respectively. All groups were exposed either to vacuum alone or to vacuum plus VUV. Our results demonstrate that halite can serve as protection against vacuum and VUV radiation, regardless of the type of microorganism. In addition, we found that the protection is higher than provided by crystals obtained from mixtures of salts. This extends the protective effects of halite documented in previous studies and reinforces the possibility to consider the crystals of this mineral as potential preservation structures in airless bodies or as vehicles for the interplanetary transfer of microorganisms.
Small rocky planets, as well as larger planets that suffered extensive volatile loss, tend to be drier and have thinner atmospheres as compared to Earth. Such planets probably outnumber worlds better ...endowed with volatiles, being the most common habitable planets. For the subgroup of fast rotators following eccentric orbits, atmospheres suffer radiative forcing and their heat capacity provides a method for gauging atmospheric thickness and surface conditions. We further explore the model presented in a previous paper and apply it to real and hypothetical exoplanets in the habitable zone of various classes of stars, simulating atmospheric and orbital characteristics. For planetary eccentricities e ~0.3, the forcing-induced hypothetical temperature variation would reach ~80 K for airless planets and ~10 K for planets with substantial atmospheres. For Kepler-186 f and Kepler-442 b, assuming e ~0.1, temperature variations can reach ~24 K. We also consider habitable exomoons in circular orbits around gas giants within the habitable zone, which suffer radiative forcing due to their epicyclic motion. We study several combinations of parameters for the characterization of planets (mass, eccentricity and semi-major axis) and exomoons (mass, orbital radius, albedo and atmospheric characteristics) for different stellar types. For e ~0.3, exomoon temperature varies up to ~90 K, while for ~0.6 variations can reach ~200 K. Such exomoons may plausibly retain their volatiles by continued volcanic activity fueled by tidal dissipation. Although currently undetectable, such effects might be within reach of future Extremely Large Telescope-class telescopes and space missions with mid-infrared and coronagraphic capabilities.
We report the spectroscopic analysis of six kinematical members of the Zeta Reticuli Moving Group, one of them for the first time. We confirm the existence of the Group by establishing a common ...abundance pattern for four kinematical members. High resolution spectra yielded abundances of Si, Ca, Fe, Ni and Ba, and others. Effective temperatures were derived from the excitation & ionization equilibria of Fe lines of four stars. For these, and the remaining two members, temperatures were derived from colors and the fitting of theoretical spectra to the Hα line, and ages and masses were estimated from theoretical HR diagrams. We suggest that the Group is physical being metal-poor and ~6 Gyr old.
PDF
