41 research outputs found
Two Rare Magnetic Cataclysmic Variables with Extreme Cyclotron Features Identified in the Sloan Digital Sky Survey
Two newly identified magnetic cataclysmic variables discovered in the Sloan
Digital Sky Survey (SDSS), SDSSJ155331.12+551614.5 and SDSSJ132411.57+032050.5,
have spectra showing highly prominent, narrow, strongly polarized cyclotron
humps with amplitudes that vary on orbital periods of 4.39 and 2.6 hrs,
respectively. In the former, the spacing of the humps indicates the 3rd and 4th
harmonics in a magnetic field of ~60 MG. The narrowness of the cyclotron
features and the lack of strong emission lines imply very low temperature
plasmas and very low accretion rates, so that the accreting area is heated by
particle collisions rather than accretion shocks. The detection of rare systems
like these exemplifies the ability of the SDSS to find the lowest accretion
rate close binaries.Comment: Accepted for publication in the Astrophysical Journal, vol. 583,
February 1, 2003; slight revisions and additions in response to referee's
comments; 17 pages, 6 figures, AASTeX v4.
Discoveries from a Near-infrared Proper Motion Survey using Multi-epoch 2MASS Data
We have conducted a 4030-square-deg near-infrared proper motion survey using
multi-epoch data from the Two Micron All-Sky Survey (2MASS). We find 2778
proper motion candidates, 647 of which are not listed in SIMBAD. After
comparison to DSS images, we find that 107 of our proper motion candidates lack
counterparts at B-, R-, and I-bands and are thus 2MASS-only detections. We
present results of spectroscopic follow-up of 188 targets that include the
infrared-only sources along with selected optical-counterpart sources with
faint reduced proper motions or interesting colors. We also establish a set of
near-infrared spectroscopic standards with which to anchor near-infrared
classifications for our objects. Among the discoveries are six young field
brown dwarfs, five "red L" dwarfs, three L-type subdwarfs, twelve M-type
subdwarfs, eight "blue L" dwarfs, and several T dwarfs. We further refine the
definitions of these exotic classes to aid future identification of similar
objects. We examine their kinematics and find that both the "blue L" and "red
L" dwarfs appear to be drawn from a relatively old population. This survey
provides a glimpse of the kinds of research that will be possible through
time-domain infrared projects such as the UKIDSS Large Area Survey, various
VISTA surveys, and WISE, and also through z- or y-band enabled, multi-epoch
surveys such as Pan-STARRS and LSST.Comment: To appear in the September 2010 issue of The Astrophysical Journal,
Supplement Serie
An Initial Survey of White Dwarfs in the Sloan Digital Sky Survey
An initial assessment is made of white dwarf and hot subdwarf stars observed
in the Sloan Digital Sky Survey. In a small area of sky (190 square degrees),
observed much like the full survey will be, 269 white dwarfs and 56 hot
subdwarfs are identified spectroscopically where only 44 white dwarfs and 5 hot
subdwarfs were known previously. Most are ordinary DA (hydrogen atmosphere) and
DB (helium) types. In addition, in the full survey to date, a number of WDs
have been found with uncommon spectral types. Among these are blue DQ stars
displaying lines of atomic carbon; red DQ stars showing molecular bands of C_2
with a wide variety of strengths; DZ stars where Ca and occasionally Mg, Na,
and/or Fe lines are detected; and magnetic WDs with a wide range of magnetic
field strengths in DA, DB, DQ, and (probably) DZ spectral types. Photometry
alone allows identification of stars hotter than 12000 K, and the density of
these stars for 15<g<20 is found to be ~2.2 deg^{-2} at Galactic latitudes
29-62 deg. Spectra are obtained for roughly half of these hot stars. The
spectra show that, for 15<g<17, 40% of hot stars are WDs and the fraction of
WDs rises to ~90% at g=20. The remainder are hot sdB and sdO stars.Comment: Accepted for AJ; 43 pages, including 12 figures and 5 table
The Milky Way Tomography With SDSS. III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r 20 degrees). We find that in the region defined by 1 kpc < Z < 5 kpc and 3 kpc < R < 13 kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (< 100 pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.NSF AST-615991, AST-0707901, AST-0551161, AST-02-38683, AST-06-07634, AST-0807444, PHY05-51164NASA NAG5-13057, NAG5-13147, NNXO-8AH83GPhysics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) PHY 08-22648U.S. National Science FoundationMarie Curie Research Training Network ELSA (European Leadership in Space Astrometry) MRTN-CT-2006-033481Fermi Research Alliance, LLC, United States Department of Energy DE-AC02-07CH11359Alfred P. Sloan FoundationParticipating InstitutionsJapanese MonbukagakushoMax Planck SocietyHigher Education Funding Council for EnglandMcDonald Observator
L Dwarfs Found in Sloan Digital Sky Survey Commissioning Data II. Hobby-Eberly Telescope Observations
Low dispersion optical spectra have been obtained with the Hobby-Eberly
Telescope of 22 very red objects found in early imaging data from the Sloan
Digital Sky Survey. The objects are assigned spectral types on the 2MASS system
(Kirkpatrick et al. 1999) and are found to range from late M to late L. The
red- and near-infrared colors from SDSS and 2MASS correlate closely with each
other, and most of the colors are closely related to spectral type in this
range; the exception is the (i^* - z^*) color, which appears to be independent
of spectral type between about M7 and L4. The spectra suggest that this
independence is due to the disappearance of the TiO and VO absorption in the
i-band for later spectral types; to the presence of strong Na I and K I
absorption in the i-band; and to the gradual disappearance of the 8400 Angstrom
absorption of TiO and FeH in the z-band.Comment: 20 pages, 7 figures, accepted by AJ, a version with higher resolution
figures can be found at ftp://ftp.astro.psu.edu/pub/dps/hetld.p
The Milky Way Tomography with SDSS: III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence
stars with r<20 and proper-motion measurements derived from SDSS and POSS
astrometry, including ~170,000 stars with radial-velocity measurements from the
SDSS spectroscopic survey. Distances to stars are determined using a
photometric parallax relation, covering a distance range from ~100 pc to 10 kpc
over a quarter of the sky at high Galactic latitudes (|b|>20 degrees). We find
that in the region defined by 1 kpc <Z< 5 kpc and 3 kpc <R< 13 kpc, the
rotational velocity for disk stars smoothly decreases, and all three components
of the velocity dispersion increase, with distance from the Galactic plane. In
contrast, the velocity ellipsoid for halo stars is aligned with a spherical
coordinate system and appears to be spatially invariant within the probed
volume. The velocity distribution of nearby ( kpc) K/M stars is complex,
and cannot be described by a standard Schwarzschild ellipsoid. For stars in a
distance-limited subsample of stars (<100 pc), we detect a multimodal velocity
distribution consistent with that seen by HIPPARCOS. This strong
non-Gaussianity significantly affects the measurements of the velocity
ellipsoid tilt and vertex deviation when using the Schwarzschild approximation.
We develop and test a simple descriptive model for the overall kinematic
behavior that captures these features over most of the probed volume, and can
be used to search for substructure in kinematic and metallicity space. We use
this model to predict further improvements in kinematic mapping of the Galaxy
expected from Gaia and LSST.Comment: 90 pages, 26 figures, submitted to Ap
Characterization of M,L and T dwarfs in the Sloan Digital Sky Survey
An extensive sample of M, L and T dwarfs identified in the Sloan Digital Sky
Survey (SDSS) has been compiled. The sample of 718 dwarfs includes 677 new
objects (629 M dwarfs, 48 L dwarfs) together with 41 that have been previously
published. All new objects and some of the previously published ones have new
optical spectra obtained either with the SDSS spectrographs or with the Apache
Point Observatory 3.5m ARC telescope. Spectral types and SDSS colors are
available for all objects; approximately 35% also have near-infrared magnitudes
measured by 2MASS or on the Mauna Kea system. We use this sample to
characterize the color--spectral type and color--color relations of late type
dwarfs in the SDSS filters, and to derive spectroscopic and photometric
parallax relations for use in future studies of the luminosity and mass
functions based on SDSS data. We find that the (i*-z*) and (i*-J) colors
provide good spectral type and absolute magnitude (M_i*) estimates for M and L
dwarfs. Our distance estimates for the current sample indicate that SDSS is
finding early M dwarfs out to about 1.5 kpc, L dwarfs to approximately 100 pc
and T dwarfs to near 20 pc. The T dwarf photometric data show large scatter and
are therefore less reliable for spectral type and distance estimation.Comment: 46 pages, 14 figures (24 pages of figures), Accepted for publication
in the Astronomical Journa
Cataclysmic Variables from SDSS I. The First Results
The commissioning year of the Sloan Digital Sky Survey has demonstrated that
many cataclysmic variables have been missed in previous surveys with brighter
limits. We report the identification of 22 cataclysmic variables, of which 19
are new discoveries and 3 are known systems (SW UMa, BH Lyn and Vir4). A
compendium of positions, colors and characteristics of these systems obtained
from the SDSS photometry and spectroscopy is presented along with data obtained
during follow-up studies with the Apache Point Observatory (APO) and Manastash
Ridge Observatory (MRO) telescopes. We have determined orbital periods for 3 of
the new systems: two show dwarf nova outbursts, and the third is a likely
magnetic system with eclipses of its region of line emission. Based on these
results, we expect the completed survey to locate at least 400 new CVs. Most of
these will be faint systems with low accretion rates that will provide new
constraints on binary evolution models.Comment: 26 pages, 11 figures, 7 tables, accepted for publication in A
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected