112 research outputs found
The Color Distributions of Globular Clusters in Virgo Elliptical Galaxies
This Letter presents the color distributions of the globular cluster (GC)
systems of 12 Virgo elliptical galaxies, measured using data from the Hubble
Space Telescope. Bright galaxies with large numbers of detected GC's show two
distinct cluster populations with mean V-I colors near 1.01 and 1.26. The GC
population of M86 is a clear exception; its color distribution shows a single
sharp peak near V-I=1.03. The absence of the red population in this galaxy, and
the consistency of the peak colors in the others, may be indications of the
origins of the two populations found in most bright elliptical galaxies.Comment: 5 pages, 1 figure, to be published in ApJ Letters Corrections to
introductio
A Survey of Open Clusters in the u'g'r'i'z' Filter System: I. Results for NGC2548 (M48)
We present initial results of a photometric survey of open star clusters,
primarily in the southern hemisphere, taken in the u'g'r'i'z' filter system.
While our entire observed sample covers more than 100 clusters, here we present
data for NGC2548 (M48) which is a cluster characterized in the UBV and DDO
photometric systems. We compare our results to the published values from other
observers and to the Padova theoretical isochrones and metallicity curves.
These observations demonstrate that the u'g'r'i'z' filters can play an
important role in determining the metallicity of stars and clusters. We begin
this series of papers with a study of NGC2548 because we have obtained data of
this cluster not only with our main program telescope, the CTIO Curtis-Schmidt,
but also with the US Naval Observatory (USNO) 1.0m telescope (the telescope
used to define the u'g'r'i'z' system), and the Sloan Digital Sky Survey (SDSS)
0.5m Photometric Telescope (the photometric monitoring telescope used to
calibrate the SDSS 2.5m telescope imaging data). We have used the data from
this study to validate our ability to transform measurements obtained on other
telescopes to the standard USNO 1.0m u'g'r'i'z' system. This validation is
particularly important for very red stars, for which the original u'g'r'i'z'
standard star network is poorly constrained.Comment: 32 pages, 8 figures. Complete, machine-readable versions of Tables
4-6 available at http://home.fnal.gov/~dtucker/OpenClusters/NGC2548/ .
Accepted for publication in the Astronomical Journa
SDSS J092455.87+021924.9: an Interesting Gravitationally Lensed Quasar from the Sloan Digital Sky Survey
We report the discovery of a new gravitationally lensed quasar from the Sloan
Digital Sky Survey, SDSS J092455.87+021924.9 (SDSS J0924+0219). This object was
selected from among known SDSS quasars by an algorithm that was designed to
select another known SDSS lensed quasar (SDSS 1226-0006A,B). Five separate
components, three of which are unresolved, are identified in photometric
follow-up observations obtained with the Magellan Consortium's 6.5m Walter
Baade telescope at Las Campanas Observatory. Two of the unresolved components
(designated A and B) are confirmed to be quasars with z=1.524; the velocity
difference is less than 100 km sec^{-1} according to spectra taken with the W.
M. Keck Observatory's Keck II telescope on Mauna Kea. A third stellar
component, designated C, has the colors of a quasar with redshift similar to
components A and B. The maximum separation of the point sources is 1.78". The
other two sources, designated G and D, are resolved. Component G appears to be
the best candidate for the lensing galaxy. Although component D is near the
expected position of the fourth lensed component in a four image lens system,
its properties are not consistent with being the image of a quasar at z~1.5.
Nevertheless, the identical redshifts of components A and B and the presence of
component C strongly suggest that this object is a gravitational lens. Our
observations support the idea that a foreground object reddens the fourth
lensed component and that another unmodeled effect (such as micro- or
milli-lensing) demagnificates it, but we cannot rule out the possibility that
SDSS0924+0219 is an example of the relatively rare class of ``three component''
lens systems.Comment: 24 pages, 6 figures, accepted by A
Stellar Populations of Dwarf Elliptical Galaxies: UBVRI Photometry of Dwarf Elliptical Galaxies in the Virgo Cluster
We present UBVRI surface photometry for 16 dwarf elliptical galaxies in the
Virgo Cluster with previously measured kinematic properties. The global optical
colors are red, with median values for the sample of 0.24 +/- 0.03 in (U-B),
0.77 +/- 0.02 in (B-V), and 1.02 +/- 0.03 in (V-I). We recover the well known
color-magnitude relation for cluster galaxies, but find no significant
difference in dominant stellar population between rotating and non-rotating
dwarf elliptical galaxies; the average age of the dominant stellar population
is 5-7 Gyr in all 16 galaxies in this sample. Analysis of optical spectra
confirm these age estimates and indicate Fe and Mg abundances in the range of
1/20th to 1/3 of solar, as expected for low luminosity galaxies. Based on Lick
indices and simple stellar population models, the derived [alpha/Fe] ratios are
sub-solar to solar, indicating a more gradual chemical enrichment history for
dEs as compared to giant elliptical galaxies in the Virgo Cluster. These
observations confirm the marked difference in stellar population and stellar
distribution between dwarf and giant elliptical galaxies and further
substantiate the need for alternative evolutionary scenarios for the lowest
mass cluster galaxies. We argue that it is likely that several different
physical mechanisms played a significant role in the production of the Virgo
cluster dE galaxies including in situ formation, infall of dEs that were once
part of Local Group analogs, and transformation of dwarf irregular galaxies by
the cluster environment. The observations support the hypothesis that a large
fraction of the Virgo cluster dEs are formed by ram pressure stripping of gas
from infalling dIs.Comment: 37 pages, 8 figures (2 color). Accepted to AJ (scheduled for Dec.
2004
An Improved Photometric Calibration of the Sloan Digital Sky Survey Imaging Data
We present an algorithm to photometrically calibrate wide field optical
imaging surveys, that simultaneously solves for the calibration parameters and
relative stellar fluxes using overlapping observations. The algorithm decouples
the problem of "relative" calibrations, from that of "absolute" calibrations;
the absolute calibration is reduced to determining a few numbers for the entire
survey. We pay special attention to the spatial structure of the calibration
errors, allowing one to isolate particular error modes in downstream analyses.
Applying this to the Sloan Digital Sky Survey imaging data, we achieve ~1%
relative calibration errors across 8500 sq.deg. in griz; the errors are ~2% for
the u band. These errors are dominated by unmodelled atmospheric variations at
Apache Point Observatory. These calibrations, dubbed "ubercalibration", are now
public with SDSS Data Release 6, and will be a part of subsequent SDSS data
releases.Comment: 16 pages, 17 figures, matches version accepted in ApJ. These
calibrations are available at http://www.sdss.org/dr
Sloan Digital Sky Survey Imaging of Low Galactic Latitude Fields: Technical Summary and Data Release
The Sloan Digital Sky Survey (SDSS) mosaic camera and telescope have obtained
five-band optical-wavelength imaging near the Galactic plane outside of the
nominal survey boundaries. These additional data were obtained during
commissioning and subsequent testing of the SDSS observing system, and they
provide unique wide-area imaging data in regions of high obscuration and star
formation, including numerous young stellar objects, Herbig-Haro objects and
young star clusters. Because these data are outside the Survey regions in the
Galactic caps, they are not part of the standard SDSS data releases. This paper
presents imaging data for 832 square degrees of sky (including repeats), in the
star-forming regions of Orion, Taurus, and Cygnus. About 470 square degrees are
now released to the public, with the remainder to follow at the time of SDSS
Data Release 4. The public data in Orion include the star-forming region NGC
2068/NGC 2071/HH24 and a large part of Barnard's loop.Comment: 31 pages, 9 figures (3 missing to save space), accepted by AJ, in
press, see http://photo.astro.princeton.edu/oriondatarelease for data and
paper with all figure
A Survey of z>5.7 Quasars in the Sloan Digital Sky Survey IV: Discovery of Seven Additional Quasars
We present the discovery of seven quasars at z>5.7, selected from ~2000 deg^2
of multicolor imaging data of the Sloan Digital Sky Survey (SDSS). The new
quasars have redshifts z from 5.79 to 6.13. Five are selected as part of a
complete flux-limited sample in the SDSS Northern Galactic Cap; two have larger
photometric errors and are not part of the complete sample. One of the new
quasars, SDSS J1335+3533 (z=5.93), exhibits no emission lines; the 3-sigma
limit on the rest-frame equivalent width of Ly alpha+NV line is 5 A. It is the
highest redshift lineless quasar known, and could be a gravitational lensed
galaxy, a BL Lac object or a new type of quasar. Two new z>6 quasars, SDSS
1250+3130 (z=6.13) and SDSS J1137+3549 (z=6.01), show deep Gunn-Peterson
absorption gaps in Ly alpha. These gaps are narrower the complete Gunn-Peterson
absorption troughs observed among quasars at z>6.2 and do not have complete Ly
beta absorption.Comment: AJ in press, 16 pages, 3 figure
The Fifth Data Release of the Sloan Digital Sky Survey
This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky
Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and
represents the completion of the SDSS-I project (whose successor, SDSS-II will
continue through mid-2008). It includes five-band photometric data for 217
million objects selected over 8000 square degrees, and 1,048,960 spectra of
galaxies, quasars, and stars selected from 5713 square degrees of that imaging
data. These numbers represent a roughly 20% increment over those of the Fourth
Data Release; all the data from previous data releases are included in the
present release. In addition to "standard" SDSS observations, DR5 includes
repeat scans of the southern equatorial stripe, imaging scans across M31 and
the core of the Perseus cluster of galaxies, and the first spectroscopic data
from SEGUE, a survey to explore the kinematics and chemical evolution of the
Galaxy. The catalog database incorporates several new features, including
photometric redshifts of galaxies, tables of matched objects in overlap regions
of the imaging survey, and tools that allow precise computations of survey
geometry for statistical investigations.Comment: ApJ Supp, in press, October 2007. This paper describes DR5. The SDSS
Sixth Data Release (DR6) is now public, available from http://www.sdss.or
Optimization of the Observing Cadence for the Rubin Observatory Legacy Survey of Space and Time: A Pioneering Process of Community-focused Experimental Design
© 2021. The Author(s). Published by the American Astronomical Society. This work may be used under the terms of the Creative Commons Attribution 4.0 licence. https://creativecommons.org/licenses/by/4.0/Vera C. Rubin Observatory is a ground-based astronomical facility under construction, a joint project of the National Science Foundation and the U.S. Department of Energy, designed to conduct a multipurpose 10 yr optical survey of the Southern Hemisphere sky: the Legacy Survey of Space and Time. Significant flexibility in survey strategy remains within the constraints imposed by the core science goals of probing dark energy and dark matter, cataloging the solar system, exploring the transient optical sky, and mapping the Milky Way. The surveyâs massive data throughput will be transformational for many other astrophysics domains and Rubinâs data access policy sets the stage for a huge community of potential users. To ensure that the survey science potential is maximized while serving as broad a community as possible, Rubin Observatory has involved the scientific community at large in the process of setting and refining the details of the observing strategy. The motivation, history, and decision-making process of this strategy optimization are detailed in this paper, giving context to the science-driven proposals and recommendations for the survey strategy included in this Focus Issue.Peer reviewedFinal Published versio
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