130 research outputs found
Cataclysmic Variables in the SUPERBLINK Proper Motion Survey
We have discovered a new high proper motion cataclysmic variable (CV) in the
SUPERBLINK proper motion survey, which is sensitive to stars with proper
motions greater than 40 mas/yr. This CV was selected for follow-up observations
as part of a larger search for CVs selected based on proper motions and their
NUV-V and V-K colors. We present spectroscopic observations from the 2.4m
Hiltner Telescope at MDM Observatory. The new CV's orbital period is near 96
minutes, its spectrum shows the double-peaked Balmer emission lines
characteristic of quiescent dwarf novae, and its V magnitude is near 18.2.
Additionally, we present a full list of known CVs in the SUPERBLINK catalog.Comment: Accepted for publication in The Astronomical Journal, 22 pages, 6
figure
Chemodynamical Ages of Small-Scale Kinematic Structures of the Galactic Disc in the Solar Neighborhood from ~280,000 K and M Dwarfs
We combine photometric metallicities with astrometry from Gaia DR3 to examine
the chemodynamic structure of ~280,000 K dwarfs in the Solar Neighborhood (SN).
In kinematics, we observe ridges/clumps of "kinematic groups", like studies of
more massive main-sequence stars. Here we note clear differences in both
metallicity and vertical velocity as compared to the surrounding regions in
velocity space and hypothesize this is due to differences in mean age. To test
this, we develop a method to estimate the age distribution of sub-populations
of stars. In this method, we use GALAH data to define probability distributions
of W vs. [M/H] in age bins of 2 Gyr and determine optimal age distributions as
the best fit weighted sum of these distributions. This process is then
validated using the GALAH subset. We estimate the probable age distribution for
regions in the kinematic plane, where we significant sub-structure that is
correlated with the kinematic groups. Most notably, we find an age gradient
across the Hercules streams that is correlated with birth radius. Finally, we
examine the bending and breathing modes in the kinematic plane and find
correlations with age, where the breathing amplitude decrease with age and the
bending amplitude is constant, except for a large increase for stars of 10-12
Gyr. This is one of the first studies to examine these chemodynamics in the SN
using primarily low-mass stars and we hope these findings can better constrain
dynamical models of the Milky Way due to the increase in resolution the sample
size provides.Comment: 17 pages, 12 figure
They might be giants: luminosity class, planet frequency, and planet-metallicity relation of the coolest Kepler target stars
We estimate the stellar parameters of late K and early M type Kepler target
stars. We obtain medium resolution visible spectra of 382 stars with Kp-J>2
(~K5 and later spectral type). We determine luminosity class by comparing the
strength of gravity-sensitive indices (CaH, K I, Ca II, and Na I) to their
strength in a sample of stars of known luminosity class. We find that giants
constitute 96+-% of the bright (Kp<14) Kepler target stars, and 7+-3% of dim
(Kp>14) stars, significantly higher than fractions based on the stellar
parameters quoted in the Kepler Input Catalog (KIC). The KIC effective
temperatures are systematically (110 +15 -35} K) higher than temperatures we
determine from fitting our spectra to PHOENIX stellar models. Through Monte
Carlo simulations of the Kepler exoplanet candidate population, we find a
planet occurrence of 0.36+-0.08 when giant stars are properly removed, somewhat
higher than when a KIC log(g)>4 criterion is used (0.27+-0.05). Lastly, we show
that there is no significant difference in g-r color (a probe of metallicity)
between late-type Kepler stars with transiting Earth-to-Neptune sized exoplanet
candidates and dwarf stars with no detected transits. We show that a previous
claimed offset between these two populations is most likely an artifact of
including a large number of misidentified giants.Comment: Accepted to Ap
Proper Motions of Faint UV-Bright Sources in the Sandage Two-color Survey of the Galactic Plane
Proper motions with values >10 mas/yr or <-10 mas/yr have been extracted from
the USNO-B1.0 and Tycho II catalogues for all Lanning UV-bright sources
identified in the Sandage Two-color Survey of the Galactic Plane and presented
in Papers I-VI. Of the 572 sources examined, we find at least 213 which exhibit
a significantly large proper motion. Based on the location of the sources in a
reduced proper motion diagram, we demonstrate that about two thirds of the high
proper motion sources are likely or very likely to be heretofore unidentified
white dwarfs.Comment: 15 pages, to appear in Publications of the Astronomical Society of
the Pacifi
Wide companions to Hipparcos stars within 67 pc of the Sun
A catalog of common-proper-motion (CPM) companions to stars within 67 pc of
the Sun is constructed based on the SUPERBLINK proper-motion survey. It
contains 1392 CPM pairs with angular separations 30" < \rho < 1800", relative
proper motion between the two components less than 25 mas/yr, magnitudes and
colors of the secondaries consistent with those of dwarfs in the (M_V,V-J)
diagram. In addition, we list 21 candidate white-dwarf CPM companions with
separations under 300", about half of which should be physical. We estimate a
0.31 fraction of pairs with red-dwarf companions to be physical systems (about
425 objects), while the rest (mostly wide pairs) are chance alignments. For
each candidate companion, the probability of a physical association is
evaluated. The distribution of projected separations s of the physical pairs
between 2 kAU and 64 kAU follows f(s) ~ s^{-1.5}, which decreases faster than
\"Opik's law. We find that Solar-mass dwarfs have no less than 4.4% +/- 0.3%
companions with separations larger than 2 kAU, or 3.8% +/- 0.3% per decade of
orbital separation in the 2 to 16 kAU range. The distribution of mass ratio of
those wide companions is approximately uniform in the 0.1<q<1.0 range, although
we observe a dip at q=0.5 which, if confirmed, could be evidence of bimodal
distribution of companion masses. New physical CPM companions to two exoplanet
host stars are discovered.Comment: To appear in the Astronomical Journal. Electronic data table
available on request from the author
Spectroscopic confirmation of UV-bright white dwarfs from the Sandage Two-Color Survey of the Galactic Plane
We present spectroscopic observations confirming the identification of hot
white dwarfs among UV-bright sources from the Sandage Two-color Survey of the
Galactic plane and listed in the Lanning (Lan) catalog of such sources. A
subsample of 213 UV bright Lan sources have been identified as candidate white
dwarfs based on the detection of a significant proper motion. Spectroscopic
observations of 46 candidates with the KPNO 2.1m telescope confirm 30 sources
to be hydrogen white dwarfs with subtypes in the DA1-DA6 range, and with one of
the stars (Lan 161) having an unresolved M dwarf as a companion. Five more
sources are confirmed to be helium white dwarfs, with subtypes from DB3 to DB6.
One source (Lan 364) is identified as a DZ 3 white dwarf, with strong lines of
calcium. Three more stars are found to have featureless spectra (to within
detection limits), and are thus classified as DC white dwarfs. In addition,
three sources are found to be hot subdwarfs: Lan 20 and Lan 480 are classified
as sdOB, and Lan 432 is classified sdB. The remaining four objects are found to
be field F star interlopers. Physical parameters of the DA and DB white dwarfs
are derived from model fits.Comment: To appear in the Astronomical Journa
Vetting the Lobster Diagram: Searching for Unseen Companions in Wide Binaries using NASA Space Exoplanet Missions
Over the past decade, the number of known wide binary systems has
exponentially expanded thanks to the release of data from the Gaia Mission.
Some of these wide binary systems are actually higher-order multiples, where
one of the components is an unresolved binary itself. One way to search for
these systems is by identifying overluminous components in the systems. In this
study, we examine 4947 K+K wide binary pairs from the SUPERWIDE catalog and
quantify the relative color and luminosity of the components to find evidence
for additional, unresolved companions. The method is best illustrated in a
graph we call the "Lobster diagram." To confirm that the identified
overluminous components are close binary systems, we cross-match our wide
binaries with the TESS, K2 and Kepler archives and search for the signs of
eclipses and fast stellar rotation modulation in the light curves. We find that
of the wide binaries which contain an eclipsing system are
identified to be overluminous in the "Lobster Diagram" and of
the wide binaries which contain a component showing fast rotation () days
also show an overluminous component. From these results, we calculate a revised
lower limit on the higher-order multiplicity fraction for K+K wide binaries of
. We also examine the higher-order multiplicity fraction as a
function of projected physical separation and metallicity. The fraction is
unusually constant as a function of projected physical separation while we see
no statistically significant evidence that the fraction varies with
metallicity.Comment: Submitted and accepted to Ap
Twenty-three new ultra-cool subdwarfs from the Sloan Digital Sky Survey
A search of the Sloan Digital Sky Survey spectroscopic database has turned up
23 new ultra-cool subdwarfs, low-mass metal-poor stars of spectral subtype M
7.0 or later. Spectra from these red objects all show very strong molecular
bands of CaH but relatively weak bands of TiO, indicative of a cool, metal-poor
atmosphere. Five of the stars are formally classified as M subdwarfs
(sdM7.0-sdM8.5), 13 as more metal-poor extreme subdwarfs (esdM7.0-esdM8.0), and
five as extremely metal-poor ultra subdwarfs (usdM7.0-usdM7.5). In the
[H_r,r-z] reduced proper motion diagram, these subdwarfs clearly populate the
locus of low-luminosity stars with halo kinematics. It is argued that the
objects are all very low-mass, metal-poor stars from the Galactic halo
(Population II). These new discoveries more than double the census of
spectroscopically confirmed ultra-cool subdwarfs. We show that the stars stand
out remarkably in the [g-r,r-i] color-color diagram; a proposed color and
proper motion selection scheme is expected to be extremely efficient in
identifying more of these old, very low mass stars in the vicinity of the Sun.Comment: 4 pages, submitted to the Astrophysical Journal Letters, version 2
includes minor correction
The Na 8200 Angstrom Doublet as an Age Indicator in Low-Mass Stars
We investigate the use of the gravity sensitive neutral sodium (NaI) doublet
at 8183 Angstroms 8195 Angstroms (Na 8200 Angstrom doublet) as an age indicator
for M dwarfs. We measured the Na doublet equivalent width (EW) in giants, old
dwarfs, young dwarfs, and candidate members of the Beta Pic moving group using
medium resolution spectra. Our Na 8200 Angstrom doublet EW analysis shows that
the feature is useful as an approximate age indicator in M-type dwarfs with
(V-K_s) >= 5.0, reliably distinguishing stars older and younger than 100 Myr. A
simple derivation of the dependence of the Na EW on temperature and gravity
supports the observational results. An analysis of the effects of metallicity
show that this youth indicator is best used on samples with similar
metallicity. The age estimation technique presented here becomes useful in a
mass regime where traditional youth indicators are increasingly less reliable,
is applicable to other alkali lines, and will help identify new-low mass
members in other young clusters and associations.Comment: 26 pages, 8 figures, accepted to the Astronomical Journa
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