26 research outputs found
Fine structure of the age-chromospheric activity relation in solar-type stars I: The Ca II infrared triplet: Absolute flux calibration
Strong spectral lines are useful indicators of stellar chromospheric
activity. They are physically linked to the convection efficiency, differential
rotation, and angular momentum evolution and are a potential indicator of age.
However, for ages > 2 Gyr, the age-activity relationship remains poorly
constrained thus hampering its full application. The Ca II infrared triplet
(IRT lines) has been poorly studied compared to classical chromospheric
indicators. We report in this paper absolute chromospheric fluxes in the three
Ca II IRT lines, based on a new calibration tied to up-to-date model
atmospheres. We obtain the Ca II IRT absolute fluxes for 113 FGK stars from
high signal-to-noise ratio and high-resolution spectra covering an extensive
domain of chromospheric activity levels. We perform an absolute continuum flux
calibration for the Ca II IRT lines anchored in atmospheric models calculated
as an explicit function of effective temperatures, metallicity, and gravities
avoiding the degeneracy present in photometric continuum calibrations based
solely on color indices. The internal uncertainties achieved for continuum
absolute flux calculations are 2\% of the solar chromospheric flux, one order
of magnitude lower than photometric calibrations. We gauge the impact of
observational errors on the final chromospheric fluxes due to the absolute
continuum flux calibration and find that uncertainties are
properly mitigated by the photospheric correction leaving [Fe/H] as the
dominating factor in the chromospheric flux uncertainty. Across the FGK
spectral types, the Ca II IRT lines are sensitive to chromospheric activity.
The reduced internal uncertainties reported here enable us to build a new
chromospheric absolute flux scale and explore the age-activity relation from
the active regime down to very low activity levels and a wide range of , mass, [Fe/H], and age.Comment: 12 pages, 12 figures, 6 tables, Accepted for publication on A&A.
Abstract edited to comply with arXiv standards regarding the number of
character
Consistent metallicity scale for cool dwarfs and giants. A benchmark test using the Hyades
In several instances chemical abundances of dwarf and giant stars are used
simultaneously under the assumption that they share the same abundance scale.
This assumption might have implications in different astrophysical contexts. We
aim to ascertain a methodology capable of producing a consistent metallicity
scale for giants and dwarfs. To achieve that, we analyzed giants and dwarfs in
the Hyades open cluster. All these stars have archival high-resolution
spectroscopic data obtained with HARPS and UVES. In addition, the giants have
interferometric measurements of the angular diameters. We analyzed the sample
with two methods. The first method constrains the atmospheric parameters
independently from spectroscopy. For that we present a novel calibration of
microturbulence based on 3D model atmospheres. The second method is the
classical spectroscopic based on Fe lines. We also tested two line lists in an
attempt to minimize possible non-LTE effects and to optimize the treatment of
the giants. We show that it is possible to obtain a consistent metallicity
scale between dwarfs and giants. The preferred method should constrain the
three parameters , , and independent of
spectroscopy. In particular, the lines should be chosen to be free of blends in
the spectra of giants. When attention is paid to the line list, the classical
spectroscopic method can also produce consistent results. The metallicities
derived with the well-constrained set of stellar parameters are consistent
independent of the line list used. Therefore, for this cluster we favor the
metallicity of +0.180.03 dex obtained with this method. The classical
spectroscopic analysis, using the line list optimized for the giants, provides
a metallicity of +0.140.03 dex, in agreement with previous works.Comment: 19 pages, 6 figures, 10 tables. Accepted for publication in A&
Faint solar analogs: at the limit of no reddening
The flux distribution of solar analogs is required for calculating the
spectral albedo of Solar System bodies such as asteroids and trans-Neptunian
objects. Ideally a solar analog should be comparably faint as the target of
interest, but only few analogs fainter than V = 9 were identified so far. Only
atmospheric parameters equal to solar guarantee a flux distribution equal to
solar as well, while only photometric colors equal to solar do not. Reddening
is also a factor to consider when selecting faint analog candidates. We
implement the methodology for identifying faint analogs at the limit of
precision allowed by current spectroscopic surveys. We quantify the precision
attainable for the atmospheric parameters effective temperature (),
metallicity ([Fe/H]), surface gravity (log ) when derived from moderate low
resolution (R=8000) spectra with S/N . We calibrated and
[Fe/H] as functions of equivalent widths of spectral indices by means of the
PCA regression. We derive log , mass, radius, and age from the atmospheric
parameters, Gaia parallaxes and evolutionary tracks. We obtained
/[Fe/H]/log with precision of 97 K/0.06 dex/0.05 dex. We identify
five solar analogs with (located at pc): HIP 991, HIP
5811, HIP 69477, HIP 55619 and HIP 61835. Other six stars have close
to solar but slightly lower [Fe/H]. Our analogs show no evidence of reddening
but for four stars, which present mag, translating to at
least a 200 K decrease in photometric .Comment: Paper accepted. Fundamental parameters of the solar analogs are in
Table
MARVELS-1: A face-on double-lined binary star masquerading as a resonant planetary system; and consideration of rare false positives in radial velocity planet searches
We have analyzed new and previously published radial velocity observations of
MARVELS-1, known to have an ostensibly substellar companion in a ~6- day orbit.
We find significant (~100 m/s) residuals to the best-fit model for the
companion, and these residuals are naively consistent with an interior giant
planet with a P = 1.965d in a nearly perfect 3:1 period commensuribility
(|Pb/Pc - 3| < 10^{-4}). We have performed several tests for the reality of
such a companion, including a dynamical analysis, a search for photometric
variability, and a hunt for contaminating stellar spectra. We find many reasons
to be critical of a planetary interpretation, including the fact that most of
the three-body dynamical solutions are unstable. We find no evidence for
transits, and no evidence of stellar photometric variability. We have
discovered two apparent companions to MARVELS-1 with adaptive optics imaging at
Keck; both are M dwarfs, one is likely bound, and the other is likely a
foreground object. We explore false-alarm scenarios inspired by various
curiosities in the data. Ultimately, a line profile and bisector analysis lead
us to conclude that the ~100 m/s residuals are an artifact of spectral
contamination from a stellar companion contributing ~15-30% of the optical
light in the system. We conclude that origin of this contamination is the
previously detected radial velocity companion to MARVELS-1, which is not, as
previously reported, a brown dwarf, but in fact a G dwarf in a face-on orbit.Comment: ApJ 770, 119. 24 pp emulate ApJ style, 12 figures (One is very
large). v2: corrects two (important!) errors: A priori chance of this
alignment or worse is 0.1% (not 0.01%) and the primary has THREE total
companions (not four
Very Low-mass Stellar and Substellar Companions to Solar-like Stars from MARVELS II: A Short-period Companion Orbiting an F Star with Evidence of a Stellar Tertiary And Significant Mutual Inclination
We report the discovery via radial velocity of a short-period (P = 2.430420
\pm 0.000006 days) companion to the F-type main sequence star TYC 2930-00872-1.
A long-term trend in the radial velocities indicates the presence of a tertiary
stellar companion with days. High-resolution spectroscopy of the
host star yields T_eff = 6427 +/- 33 K, log(g) = 4.52 +/- 0.14, and
[Fe/H]=-0.04 +/- 0.05. These parameters, combined with the broad-band spectral
energy distribution and parallax, allow us to infer a mass and radius of the
host star of M_1=1.21 +/- 0.08 M_\odot and R_1=1.09_{-0.13}^{+0.15} R_\odot. We
are able to exclude transits of the inner companion with high confidence. The
host star's spectrum exhibits clear Ca H and K core emission indicating stellar
activity, but a lack of photometric variability and small v*sin(I) suggest the
primary's spin axis is oriented in a pole-on configuration. The rotational
period of the primary from an activity-rotation relation matches the orbital
period of the inner companion to within 1.5 \sigma, suggesting they are tidally
locked. If the inner companion's orbital angular momentum vector is aligned
with the stellar spin axis, as expected through tidal evolution, then it has a
stellar mass of M_2 ~ 0.3-0.4 M_\odot. Direct imaging limits the existence of
stellar companions to projected separations < 30 AU. No set of spectral lines
and no significant flux contribution to the spectral energy distribution from
either companion are detected, which places individual upper mass limits of M <
1.0 M_\odot, provided they are not stellar remnants. If the tertiary is not a
stellar remnant, then it likely has a mass of ~0.5-0.6 M_\odot, and its orbit
is likely significantly inclined from that of the secondary, suggesting that
the Kozai-Lidov mechanism may have driven the dynamical evolution of this
system.Comment: 37 pages, 7 tables, 21 figures, Accepted in A
SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems
Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II),
SDSS-III is a program of four spectroscopic surveys on three scientific themes:
dark energy and cosmological parameters, the history and structure of the Milky
Way, and the population of giant planets around other stars. In keeping with
SDSS tradition, SDSS-III will provide regular public releases of all its data,
beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an
overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5
million massive galaxies and Lya forest spectra of 150,000 quasars, using the
BAO feature of large scale structure to obtain percent-level determinations of
the distance scale and Hubble expansion rate at z<0.7 and at z~2.5. SEGUE-2,
which is now completed, measured medium-resolution (R=1800) optical spectra of
118,000 stars in a variety of target categories, probing chemical evolution,
stellar kinematics and substructure, and the mass profile of the dark matter
halo from the solar neighborhood to distances of 100 kpc. APOGEE will obtain
high-resolution (R~30,000), high signal-to-noise (S/N>100 per resolution
element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars,
measuring separate abundances for ~15 elements per star and creating the first
high-precision spectroscopic survey of all Galactic stellar populations (bulge,
bar, disks, halo) with a uniform set of stellar tracers and spectral
diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars
with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to
detect giant planets with periods up to two years, providing an unprecedented
data set for understanding the formation and dynamical evolution of giant
planet systems. (Abridged)Comment: Revised to version published in The Astronomical Journa
The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III
The third generation of the Sloan Digital Sky Survey (SDSS-III) took data from 2008 to 2014 using the original SDSS wide-field imager, the original and an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared high-resolution spectrograph, and a novel optical interferometer. All of the data from SDSS-III are now made public. In particular, this paper describes Data Release 11 (DR11) including all data acquired through 2013 July, and Data Release 12 (DR12) adding data acquired through 2014 July (including all data included in previous data releases), marking the end of SDSS-III observing. Relative to our previous public release (DR10), DR12 adds one million new spectra of galaxies and quasars from the Baryon Oscillation Spectroscopic Survey (BOSS) over an additional 3000 deg2 of sky, more than triples the number of H-band spectra of stars as part of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE), and includes repeated accurate radial velocity measurements of 5500 stars from the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The APOGEE outputs now include the measured abundances of 15 different elements for each star. In total, SDSS-III added 5200 deg2 of ugriz imaging; 155,520 spectra of 138,099 stars as part of the Sloan Exploration of Galactic Understanding and Evolution 2 (SEGUE-2) survey; 2,497,484 BOSS spectra of 1,372,737 galaxies, 294,512 quasars, and 247,216 stars over 9376 deg2; 618,080 APOGEE spectra of 156,593 stars; and 197,040 MARVELS spectra of 5513 stars. Since its first light in 1998, SDSS has imaged over 1/3 of the Celestial sphere in five bands and obtained over five million astronomical spectra. \ua9 2015. The American Astronomical Society