281 research outputs found
1-1.4 Micron Spectral Atlas of Stars
We present a catalog of J-band (1.08 um to 1.35 um) stellar spectra at low
resolution (R ~ 400). The targets consist of 105 stars ranging in spectral type
from O9.5 to M7 and luminosity classes I through V. The relatively featureless
spectra of hot stars, earlier than A4, can be used to remove the atmospheric
features which dominate ground-based J-band spectroscopy. We measure equivalent
widths for three absorption lines and nine blended features which we identify
in the spectra. Using detailed comparison with higher resolution spectra, we
demonstrate that low resolution data can be used for stellar classification,
since several features depend on the effective temperature and gravity. For
example The CN index (1.096 - 1.104 um) decreases with temperature, but the
strength of a blended feature at 1.28 um (consisting of primarily P beta)
increases. The slope of a star's spectrum can also be used to estimate its
effective temperature. The luminosity class of a star correlates with the ratio
of the Mg I (1.1831 um) line to a blend of several species at 1.16 um. Using
these indicators, a star can be classified to within several subclasses.
Fifteen stars with particularly high and low metal abundances are included in
the catalog and some spectral dependence on metal abundance is also found.Comment: 35 pages, 10 figures (3a-e are in gif format. For complete high
resolution figures, go to http://www.astro.ucla.edu/~malkan/newjspec/) ;
Accepted for published in ApJS; For associated spectra files, see
http://www.astro.ucla.edu/~malkan/newjspec
The WFC3 Infrared Spectroscopic Parallel (WISP) Survey
We present the WFC3 Infrared Spectroscopic Parallel (WISP) Survey. WISP is
obtaining slitless, near-infrared grism spectroscopy of ~ 90 independent,
high-latitude fields by observing in the pure parallel mode with Wide Field
Camera-3 on the Hubble Space Telescope for a total of ~ 250 orbits. Spectra are
obtained with the G102 (lambda=0.8-1.17 microns, R ~ 210) and G141 grisms
(lambda=1.11-1.67 microns, R ~ 130), together with direct imaging in the J- and
H-bands (F110W and F140W, respectively). In the present paper, we present the
first results from 19 WISP fields, covering approximately 63 square arc
minutes. For typical exposure times (~ 6400 sec in G102 and ~ 2700 sec in
G141), we reach 5-sigma detection limits for emission lines of 5 x 10^(-17)
ergs s^(-1) cm^(-2) for compact objects. Typical direct imaging 5sigma-limits
are 26.8 and 25.0 magnitudes (AB) in F110W and F140W, respectively. Restricting
ourselves to the lines measured with highest confidence, we present a list of
328 emission lines, in 229 objects, in a redshift range 0.3 < z < 3. The
single-line emitters are likely to be a mix of Halpha and [OIII]5007,4959 A,
with Halpha predominating. The overall surface density of high-confidence
emission-line objects in our sample is approximately 4 per arcmin^(2).These
first fields show high equivalent width sources, AGN, and post starburst
galaxies. The median observed star formation rate of our Halpha selected sample
is 4 Msol/year. At intermediate redshifts, we detect emission lines in galaxies
as faint as H_140 ~ 25, or M_R < -19, and are sensitive to star formation rates
down to less than 1 Msol/year. The slitless grisms on WFC3 provide a unique
opportunity to study the spectral properties of galaxies much fainter than L*
at the peak of the galaxy assembly epoch.Comment: 15 pages, 12 figures, submitted to Ap
K-Band Spectroscopy of an Obscured Massive Stellar Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC
We present infrared spectroscopy of the Antennae Galaxies (NGC 4038/4039)
with NIRSPEC at the W. M. Keck Observatory. We imaged the star clusters in the
vicinity of the southern nucleus (NGC 4039) in 0.39" seeing in K-band using
NIRSPEC's slit-viewing camera. The brightest star cluster revealed in the
near-IR (M_K(0) = -17.9) is insignificant optically, but coincident with the
highest surface brightness peak in the mid-IR (12-18 um) ISO image presented by
Mirabel et al (1998). We obtained high signal-to-noise 2.03-2.45 um spectra of
the nucleus and the obscured star cluster at R = 1900.
The cluster is very young (age ~ 4 Myr), massive (M ~ 16E6 M_sun), and
compact (density ~ 115 M_sun pc^(-3) within a 32 pc half-light radius),
assuming a Salpeter IMF (0.1-100 M_sun). Its hot stars have a radiation field
characterized by T_eff ~ 39,000 K, and they ionize a compact HII region with
n_e ~ 10^4 cm^(-3). The stars are deeply embedded in gas and dust (A_V = 9-10
mag), and their strong FUV field powers a clumpy photodissociation region with
densities n_H > 10^5 cm^(-3) on scales of ~ 200 pc, radiating L{H_2 1-0 S(1)}=
9600 L_sun.Comment: 4 pages, 4 embedded figures, uses emulateapj.sty. To appear in ApJL.
Also available at http://astro.berkeley.edu/~agilber
Extremely Red Objects from the NICMOS/HST Parallel Imaging Survey
We present a catalog of extremely red objects discovered using the NICMOS/HST
parallel imaging database and ground-based optical follow-up observations.
Within an area of 16 square arc-minutes, we detect 15 objects with and . We have also obtained K-band photometry for
a subset of the 15 EROs. All of the selected EROs imaged at
K-band have . Our objects have colors in the
range of 1.3 - 2.1, redder than the cluster ellipticals at and
nearly 1 magnitude redder than the average population selected from the F160W
images at the same depth. In addition, among only 22 NICMOS pointings, we
detected two groups or clusters in two fields, each contains 3 or more EROs,
suggesting that extremely red galaxies may be strongly clustered. At bright
magnitudes with , the ERO surface density is similar to what
has been measured by other surveys. At the limit of our sample, F160W = 21.5,
our measured surface density is 0.94 arcmin^{-2}. Excluding the two
possible groups/clusters and the one apparently stellar object, reduces the
surface density to 0.38 arcmin^{-2}.Comment: To appear in the AJ August issue. Replaced with the published versio
Enhancing Science Return During the Rapid Expansion of IRSA
The NASA/IPAC Infrared Science Archive is undergoing a rapid expansion in the portfolio of missions for which we serve data, including the recent additions of the Spitzer Heritage Archive, the WISE archive, and NASA's Planck archive. This expansion has led to more than an order of magnitude increase in data holdings within a few years, and the inclusion of catalogs up to 10 billion rows. As a result, IRSA has a special opportunity to grow its services to support not only individual IR missions, but to optimize the synergy between them. We discuss the ways in which we enhance the science return from multiple IR data sets, including data discovery, moving object “precovery,” and image cross-comparison
Spitzer 70 Micron Source Counts in GOODS-North
We present ultradeep Spitzer 70 μm observations of GOODS-North (Great Observatories Origins Deep Survey). For the first time, the turnover in the 70 μm Euclidean-normalized differential source counts is observed. We derive source counts down to a flux density of 1.2 mJy. From the measured source counts and fluctuation analysis, we estimate a power-law approximation of the faint 70 μm source counts of dN/dS ∝ S^−1.6, consistent with that observed for the faint 24 μm sources. An extrapolation of the 70 μm source counts to zero flux density implies a total extragalactic background light (EBL) of 7.4 ± 1.9 nW m^−2 sr^−1. The source counts above 1.2 mJy account for about 60% of the estimated EBL. From fluctuation analysis, we derive a photometric confusion level of σc = 0.30 ± 0.15 mJy (q = 5) for the Spitzer 70 μm band
Science Validation of the Spitzer Source List
The Spitzer Science Center will produce a source list (SL) of photometry for a large subset of imaging data in the Spitzer Heritage Archive (SHA). The list will enable a large range of science projects. The primary requirement on the SL is very high reliability — with areal coverage, completeness and limiting depth being secondary considerations. The SHA at the NASA Infrared Science Archive (IRSA) will serve the SL as an enhanced data product. The SL will include data from the four channels of
IRAC (3–8 microns) and the 24 micron channel of MIPS. The Source List will include image products (mosaics) and photometric data for Spitzer observations of about 1500
square degrees and include around 30 million sources. We describe ongoing science validation of the Spitzer Source List, and discuss the range of use cases which will be
supported
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