390 research outputs found
Fraction of the radial velocity stable stars in the early observations of the Grid Giant Star Survey
The GGSS is a partially-filled, all-sky survey to identify K-giant stars with
low level of RV-variability. We study histograms of the radial velocity (RV)
variability obtained in the early phase of the Grid Giant Star Survey (GGSS,
Bizyaev et al., 2006). This part of the survey has been conducted with a very
limited nubmer of observations per star, and rough accuracy. We apply the
Monte-Carlo simulations to infer a fraction of the RV-stable stars in the
sample. Our optimistic estimate is that 20% of all considered K-giants have
RV-variability under 30 m s. Different assumptions of intrinsic
RV-variability for our stars give 12 -- 20 % of RV-stable K-giants in the
studied sample.Comment: 3 pages, 2 figures, to be published in PAS
SDSS-IV MaNGA: Ionization sources of diffuse extra-planar galactic medium
We explore sources of ionization of diffuse gas at different altitudes in
galaxies in dependence of their stellar mass, \Ha\ luminosity, and specific
star formation rate. We use the MaNGA data from SDSS-IV data release DR16
together with photoionization and shock ionization models provided by the 3MdB
database. Our sample comprises 239 edge-on galaxies, which makes our results
statistically valuable. We reach very high galactic altitudes with the help of
spectra stacking. We demonstrate that models of the gas photoionization in a
combination of young OB-stars and hot low-mass evolved stars (HOLMES) describes
the gas ionization state in the galaxies of all types on diagnostic diagrams.
Nevertheless, the shock waves may contribute to the gas ionization in massive
galaxies with passive star formation. We observe a general trend of decreasing
the fraction of the ionizing flux from OB-stars and the ionization parameter
with the altitude, while the role of the ionization by the HOLMES increases.
The biggest difference in the contribution from these types of ionizing sources
correlates with the specific star formation rate and with stellar masses of
galaxies. The HOLMES are the principal gas ionization sources in massive
galaxies with passive star formation, while OB-stars dominate the gas
ionization in low-mass galaxies with active star formation.Comment: 14 pages, 9 figures. Accepted for publication in Astronomy Letter
Structural Parameters of Stellar Disks from 2MASS Images of Edge-on Galaxies
We present results of an analysis of the J, H, and K 2MASS images of 139
spiral edge-on galaxies selected from the Revised Flat Galaxies Catalog. The
basic structural parameters scalelength (h), scaleheight (z_0), and central
surface brightness of the stellar disks (mu_0) are determined for all selected
galaxies in the NIR bands. The mean relative ratios of the scaleheights of the
thin stellar disks in the J:H:K bands are 1.16:1.08:1.00, respectively.
Comparing the scaleheights obtained from the NIR bands for the same objects, we
estimate the scaleheights of the thin stellar disks corrected for the internal
extinction. We find that the extinction-corrected scaleheight is, on average,
11% smaller than that in the K-band. Using the extinction-corrected structural
parameters, we find that the dark-to-luminous mass ratio is, on average, 1.3
for the galaxies in our sample within the framework of a simplified galactic
model. The relative thicknesses of the stellar disks z_0/h correlates with
their face-on central surface brightnesses obtained from the 2MASS images. We
also find that the scaleheight of the stellar disks shows no systematic growth
with radius in most of our galaxies.Comment: To be published in Astrophysical Journa
The Space Interferometry Mission Astrometric Grid Giant-Star Survey. III. Basic Stellar Parameters for an Extended Sample
We present results of high resolution (~ 55000) spectral observations of 830
photometrically pre-selected candidate red giants in the magnitude range of V =
9-12. We develop a pipeline for automated determination of the stellar
atmospheric parameters from these spectra and estimate T_eff, logg, [Fe/H],
microturbulence velocity, and projected rotational velocities, vsini, for the
stars. The analysis confirms that the candidate selection procedure yielded red
giants with very high success rate. We show that most of these stars are G and
K giants with slightly subsolar metallicity ([Fe/H] ~ -0.3 dex) An analysis of
Mg abundances in the sample results in consistency of the [Mg/Fe] vs [Fe/H]
trend with published results.Comment: Accepted by A
The Frequency of Rapid Rotation Among K Giant Stars
We present the results of a search for unusually rapidly rotating giant stars
in a large sample of K giants (~1300 stars) that had been spectroscopically
monitored as potential targets for the Space Interferometry Mission's
Astrometric Grid. The stars in this catalog are much fainter and typically more
metal-poor than those of other catalogs of red giant star rotational
velocities, but the spectra generally only have signal-to-noise (S/N) of
~20-60, making the measurement of the widths of individual lines difficult. To
compensate for this, we have developed a cross-correlation method to derive
rotational velocities in moderate S/N echelle spectra to efficiently probe this
sample for rapid rotator candidates. We have discovered 28 new red giant rapid
rotators as well as one extreme rapid rotator with a vsini of 86.4 km/s. Rapid
rotators comprise 2.2% of our sample, which is consistent with other surveys of
brighter, more metal-rich K giant stars. Although we find that the temperature
distribution of rapid rotators is similar to that of the slow rotators, this
may not be the case with the distributions of surface gravity and metallicity.
The rapid rotators show a slight overabundance of low gravity stars and as a
group are significantly more metal-poor than the slow rotators, which may
indicate that the rotators are tidally-locked binaries.Comment: Accepted for publication in ApJ. 25 pages, 9 figures, 3 tables.
Tables 1 and 2 are provided in their full form as plain text ancillary file
Insight Into the Formation of the Milky Way Through Cold Halo Substructure. III. Statistical Chemical Tagging in the Smooth Halo
We find that the relative contribution of satellite galaxies accreted at high
redshift to the stellar population of the Milky Way's smooth halo increases
with distance, becoming observable relative to the classical smooth halo about
15 kpc from the Galactic center. In particular, we determine
line-of-sight-averaged [Fe/H] and [alpha/Fe] in the metal-poor main-sequence
turnoff (MPMSTO) population along every Sloan Extension for Galactic
Understanding and Exploration (SEGUE) spectroscopic line of sight. Restricting
our sample to those lines of sight along which we do not detect elements of
cold halo substructure (ECHOS), we compile the largest spectroscopic sample of
stars in the smooth component of the halo ever observed in situ beyond 10 kpc.
We find significant spatial autocorrelation in [Fe/H] in the MPMSTO population
in the distant half of our sample beyond about 15 kpc from the Galactic center.
Inside of 15 kpc however, we find no significant spatial autocorrelation in
[Fe/H]. At the same time, we perform SEGUE-like observations of N-body
simulations of Milky Way analog formation. While we find that halos formed
entirely by accreted satellite galaxies provide a poor match to our
observations of the halo within 15 kpc of the Galactic center, we do observe
spatial autocorrelation in [Fe/H] in the simulations at larger distances. This
observation is an example of statistical chemical tagging and indicates that
spatial autocorrelation in metallicity is a generic feature of stellar halos
formed from accreted satellite galaxies.Comment: 27 pages, 8 figures, and 7 tables in emulateapj format; accepted for
publication in ApJ. Full tables can be extracted from LaTeX sourc
The Space Interferometry Mission Astrometric Grid Giant-Star Survey. I. Stellar Parameters and Radial Velocity Variability
We present results from a campaign of multiple epoch echelle spectroscopy of
relatively faint (V = 9.5-13.5 mag) red giants observed as potential
astrometric grid stars for the Space Interferometry Mission (SIM PlanetQuest).
Data are analyzed for 775 stars selected from the Grid Giant Star Survey
spanning a wide range of effective temperatures (Teff), gravities and
metallicities. The spectra are used to determine these stellar parameters and
to monitor radial velocity (RV) variability at the 100 m/s level. The degree of
RV variation measured for 489 stars observed two or more times is explored as a
function of the inferred stellar parameters. The percentage of radial velocity
unstable stars is found to be very high -- about 2/3 of our sample. It is found
that the fraction of RV-stable red giants (at the 100 m/s level) is higher
among stars with Teff \sim 4500 K, corresponding to the calibration-independent
range of infrared colors 0.59 < (J-K_s)_0 < 0.73. A higher percentage of
RV-stable stars is found if the additional constraints of surface gravity and
metallicity ranges 2.3< log g < 3.2 and -0.5 < [Fe/H] < -0.1, respectively, are
applied. Selection of stars based on only photometric values of effective
temperature (4300 K < Teff < 4700 K) is a simple and effective way to increase
the fraction of RV-stable stars. The optimal selection of RV-stable stars,
especially in the case when the Washington photometry is unavailable, can rely
effectively on 2MASS colors constraint 0.59 < (J-K_s)_0 < 0.73. These results
have important ramifications for the use of giant stars as astrometric
references for the SIM PlanetQuest.Comment: Astronomical Journal, in press, 22 pages, 11 Postscript figures, uses
aastex.cl
Mildly Suppressed Star Formation in Central Regions of MaNGA Seyfert Galaxies
Negative feedback from accretion onto super-massive black holes (SMBHs), that
is to remove gas and suppress star formation in galaxies, has been widely
suggested. However, for Seyfert galaxies which harbor less active, moderately
accreting SMBHs in the local universe, the feedback capability of their black
hole activity is elusive. We present spatially-resolved H measurements
to trace ongoing star formation in Seyfert galaxies and compare their specific
star formation rate with a sample of star-forming galaxies whose global galaxy
properties are controlled to be the same as the Seyferts. From the comparison
we find that the star formation rates within central kpc of Seyfert galaxies
are mildly suppressed as compared to the matched normal star forming galaxies.
This suggests that the feedback of moderate SMBH accretion could, to some
extent, regulate the ongoing star formation in these intermediate to late type
galaxies under secular evolution.Comment: 12 pages, 7 figures, accepted by MNRA
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