170 research outputs found
APOGEE Kinematics I: Overview of the Kinematics of the Galactic Bulge as Mapped by APOGEE
We present the stellar kinematics across the Galactic bulge and into the disk
at positive longitudes from the SDSS-III APOGEE spectroscopic survey of the
Milky Way. APOGEE includes extensive coverage of the stellar populations of the
bulge along the mid-plane and near-plane regions. From these data, we have
produced kinematic maps of 10,000 stars across longitudes 0 deg < l < 65 deg,
and primarily across latitudes of |b| < 5 deg in the bulge region. The APOGEE
data reveal that the bulge is cylindrically rotating across all latitudes and
is kinematically hottest at the very centre of the bulge, with the smallest
gradients in both kinematic and chemical space inside the inner-most region
(l,|b|) < (5,5) deg. The results from APOGEE show good agreement with data from
other surveys at higher latitudes and a remarkable similarity to the rotation
and dispersion maps of barred galaxies viewed edge on. The thin bar that is
reported to be present in the inner disk within a narrow latitude range of |b|
< 2 deg appears to have a corresponding signature in [Fe/H] and [alpha/Fe].
Stars with [Fe/H] > -0.5 have dispersion and rotation profiles that are similar
to that of N-body models of boxy/peanut bulges. There is a smooth kinematic
transition from the thin bar and boxy bulge (l,|b|) < (15,12) deg out into the
disk for stars with [Fe/H] > -1.0, and the chemodynamics across (l,b) suggests
the stars in the inner Galaxy with [Fe/H] > -1.0 have an origin in the disk.Comment: Accepted by ApJ 15 December 201
The Sloan Digital Sky Survey Reverberation Mapping Project : systematic investigations of short-timescale CIV broad absorption line variability
We systematically investigate short-timescale (<10-day rest-frame) Civ broad absorption-line (BAL) variability to constrain quasar-wind properties and provide insights into BAL-variability mechanisms in quasars. We employ data taken by the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project, as the rapid cadence of these observations provides a novel opportunity to probe BAL variability on shorter rest-frame timescales than have previously been explored. In a sample of 27 quasars with a median of 58 spectral epochs per quasar, we have identified 15 quasars (55+18â14%), 19 of37 Civ BAL troughs (51+15â12%), and 54 of 1460 epoch pairs (3.7±0.5%) that exhibit significant CivBAL equivalent-width variability on timescales of less than 10 days in the quasar rest frame. These frequencies indicate that such variability is common among quasars and BALs, though somewhat rare among epoch pairs. Thus, models describing BALs and their behavior must account for variability on timescales down to less than a day in the quasar rest frame. We also examine a variety of spectral characteristics and find that in some cases, BAL variability is best described by ionization-state changes, while other cases are more consistent with changes in covering fraction or column density. We adopt a simple model to constrain the density and radial distance of two outflows appearing to vary by ionization-state changes, yielding outflow density lower limits consistent with previous work.PostprintPeer reviewe
2006 SQ372: A Likely Long-Period Comet from the Inner Oort Cloud
We report the discovery of a minor planet (2006 SQ372) on an orbit with a
perihelion of 24 AU and a semimajor axis of 796 AU. Dynamical simulations show
that this is a transient orbit and is unstable on a timescale of 200 Myrs.
Falling near the upper semimajor axis range of the scattered disk and the lower
semimajor axis range of the Oort Cloud, previous membership in either class is
possible. By modeling the production of similar orbits from the Oort Cloud as
well as from the scattered disk, we find that the Oort Cloud produces 16 times
as many objects on SQ372-like orbits as the scattered disk. Given this result,
we believe this to be the most distant long-period comet ever discovered.
Furthermore, our simulation results also indicate that 2000 OO67 has had a
similar dynamical history. Unaffected by the "Jupiter-Saturn Barrier," these
two objects are most likely long-period comets from the inner Oort Cloud
SDSS-III Baryon Oscillation Spectroscopic Survey data release 12 : galaxy target selection and large-scale structure catalogues
The Baryon Oscillation Spectroscopic Survey (BOSS), part of the Sloan Digital Sky Survey (SDSS) III project, has provided the largest survey of galaxy redshifts available to date, in terms of both the number of galaxy redshifts measured by a single survey, and the effective cosmological volume covered. Key to analysing the clustering of these data to provide cosmological measurements is understanding the detailed properties of this sample. Potential issues include variations in the target catalogue caused by changes either in the targeting algorithm or properties of the data used, the pattern of spectroscopic observations, the spatial distribution of targets for which redshifts were not obtained, and variations in the target sky density due to observational systematics. We document here the target selection algorithms used to create the galaxy samples that comprise BOSS. We also present the algorithms used to create large-scale structure catalogues for the final Data Release (DR12) samples and the associated random catalogues that quantify the survey mask. The algorithms are an evolution of those used by the BOSS team to construct catalogues from earlier data, and have been designed to accurately quantify the galaxy sample. The code used, designated mksample, is released with this paper.Publisher PDFPeer reviewe
Very Metal-poor Stars in the Outer Galactic Bulge Found by the Apogee Survey
Despite its importance for understanding the nature of early stellar
generations and for constraining Galactic bulge formation models, at present
little is known about the metal-poor stellar content of the central Milky Way.
This is a consequence of the great distances involved and intervening dust
obscuration, which challenge optical studies. However, the Apache Point
Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber,
high-resolution spectroscopic survey within Sloan Digital Sky Survey III
(SDSS-III), is exploring the chemistry of all Galactic stellar populations at
infrared wavelengths, with particular emphasis on the disk and the bulge. An
automated spectral analysis of data on 2,403 giant stars in twelve fields in
the bulge obtained during APOGEE commissioning yielded five stars with low
metallicity([Fe/H]), including two that are very metal-poor
[Fe/H] by bulge standards.
Luminosity-based distance estimates place the five stars within the outer
bulge, where other 1,246 of the analyzed stars may reside. A manual reanalysis
of the spectra verifies the low metallicities, and finds these stars to be
enhanced in the -elements O, Mg, and Si without significant
-pattern differences with other local halo or metal-weak thick-disk
stars of similar metallicity, or even with other more metal-rich bulge stars.
While neither the kinematics nor chemistry of these stars can yet definitively
determine which, if any, are truly bulge members, rather than denizens of other
populations co-located with the bulge, the newly-identified stars reveal that
the chemistry of metal-poor stars in the central Galaxy resembles that of
metal-weak thick-disk stars at similar metallicity.Comment: 6 pages, 3 figures, 2 table
High-resolution, H band Spectroscopy of Be Stars with SDSS-III/APOGEE: I. New Be Stars, Line Identifications, and Line Profiles
APOGEE has amassed the largest ever collection of multi-epoch,
high-resolution (R~22,500), H-band spectra for B-type emission line (Be) stars.
The 128/238 APOGEE Be stars for which emission had never previously been
reported serve to increase the total number of known Be stars by ~6%. We focus
on identification of the H-band lines and analysis of the emission peak
velocity separations (v_p) and emission peak intensity ratios (V/R) of the
usually double-peaked H I and non-hydrogen emission lines. H I Br11 emission is
found to preferentially form in the circumstellar disks at an average distance
of ~2.2 stellar radii. Increasing v_p toward the weaker Br12--Br20 lines
suggests these lines are formed interior to Br11. By contrast, the observed IR
Fe II emission lines present evidence of having significantly larger formation
radii; distinctive phase lags between IR Fe II and H I Brackett emission lines
further supports that these species arise from different radii in Be disks.
Several emission lines have been identified for the first time including
~16895, a prominent feature in the spectra for almost a fifth of the sample
and, as inferred from relatively large v_p compared to the Br11-Br20, a tracer
of the inner regions of Be disks. Unlike the typical metallic lines observed
for Be stars in the optical, the H-band metallic lines, such as Fe II 16878,
never exhibit any evidence of shell absorption, even when the H I lines are
clearly shell-dominated. The first known example of a quasi-triple-peaked Br11
line profile is reported for HD 253659, one of several stars exhibiting intra-
and/or extra-species V/R and radial velocity variation within individual
spectra. Br11 profiles are presented for all discussed stars, as are full
APOGEE spectra for a portion of the sample.Comment: accepted in A
Discovery of a Dynamical Cold Point in the Heart of the Sagittarius dSph Galaxy with Observations from the APOGEE Project
The dynamics of the core of the Sagittarius (Sgr) dwarf spheroidal (dSph)
galaxy are explored using high-resolution (R~22,500), H-band, near-infrared
spectra of over 1,000 giant stars in the central 3 deg^2 of the system, of
which 328 are identified as Sgr members. These data, among some of the earliest
observations from the SDSS-III/Apache Point Observatory Galactic Evolution
Experiment (APOGEE) and the largest published sample of high resolution Sgr
dSph spectra to date, reveal a distinct gradient in the velocity dispersion of
Sgr from 11-14 km/s for radii >0.8 degrees from center to a dynamical cold
point of 8 km/s in the Sgr center --- a trend differing from that found in
previous kinematical analyses of Sgr over larger scales that suggest a more or
less flat dispersion profile at these radii. Well-fitting mass models with
either cored and cusped dark matter distributions can be found to match the
kinematical results, although the cored profile succeeds with significantly
more isotropic stellar orbits than required for a cusped profile. It is
unlikely that the cold point reflects an unusual mass distribution. The
dispersion gradient may arise from variations in the mixture of populations
with distinct kinematics within the dSph; this explanation is suggested (e.g.,
by detection of a metallicity gradient across similar radii), but not
confirmed, by the present data. Despite these remaining uncertainties about
their interpretation, these early test data (including some from instrument
commissioning) demonstrate APOGEE's usefulness for precision dynamical studies,
even for fields observed at extreme airmasses.Comment: 15 pages, 3 figure
The Apache Point Observatory Galactic Evolution Experiment: First Detection of High Velocity Milky Way Bar Stars
Commissioning observations with the Apache Point Observatory Galactic
Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, have
produced radial velocities (RVs) for ~4700 K/M-giant stars in the Milky Way
bulge. These high-resolution (R \sim 22,500), high-S/N (>100 per resolution
element), near-infrared (1.51-1.70 um; NIR) spectra provide accurate RVs
(epsilon_v~0.2 km/s) for the sample of stars in 18 Galactic bulge fields
spanning -1-32 deg. This represents the largest
NIR high-resolution spectroscopic sample of giant stars ever assembled in this
region of the Galaxy. A cold (sigma_v~30 km/s), high-velocity peak (V_GSR \sim
+200 km/s) is found to comprise a significant fraction (~10%) of stars in many
of these fields. These high RVs have not been detected in previous MW surveys
and are not expected for a simple, circularly rotating disk. Preliminary
distance estimates rule out an origin from the background Sagittarius tidal
stream or a new stream in the MW disk. Comparison to various Galactic models
suggests that these high RVs are best explained by stars in orbits of the
Galactic bar potential, although some observational features remain
unexplained.Comment: 7 pages, 4 figures, accepted for publication in ApJ Letter
The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
The Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM) is a
dedicated multi-object RM experiment that has spectroscopically monitored a
sample of 849 broad-line quasars in a single 7 deg field with the SDSS-III
BOSS spectrograph. The RM quasar sample is flux-limited to i_psf=21.7 mag, and
covers a redshift range of 0.1<z<4.5. Optical spectroscopy was performed during
2014 Jan-Jul dark/grey time, with an average cadence of ~4 days, totaling more
than 30 epochs. Supporting photometric monitoring in the g and i bands was
conducted at multiple facilities including the CFHT and the Steward Observatory
Bok telescopes in 2014, with a cadence of ~2 days and covering all lunar
phases. The RM field (RA, DEC=14:14:49.00, +53:05:00.0) lies within the CFHT-LS
W3 field, and coincides with the Pan-STARRS 1 (PS1) Medium Deep Field MD07,
with three prior years of multi-band PS1 light curves. The SDSS-RM 6-month
baseline program aims to detect time lags between the quasar continuum and
broad line region (BLR) variability on timescales of up to several months (in
the observed frame) for ~10% of the sample, and to anchor the time baseline for
continued monitoring in the future to detect lags on longer timescales and at
higher redshift. SDSS-RM is the first major program to systematically explore
the potential of RM for broad-line quasars at z>0.3, and will investigate the
prospects of RM with all major broad lines covered in optical spectroscopy.
SDSS-RM will provide guidance on future multi-object RM campaigns on larger
scales, and is aiming to deliver more than tens of BLR lag detections for a
homogeneous sample of quasars. We describe the motivation, design and
implementation of this program, and outline the science impact expected from
the resulting data for RM and general quasar science.Comment: 25 pages, submitted to ApJS; project website at http://www.sdssrm.or
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