935 research outputs found
A Structural and Dynamical Study of Late-Type, Edge-On Galaxies: I. Sample Selection and Imaging Data
We present optical (B & R) and infrared (K_s) images and photometry for a
sample of 49 extremely late-type, edge-on disk galaxies selected from the Flat
Galaxy Catalog of Karenchentsev et al. (1993). Our sample was selected to
include galaxies with particularly large axial ratios, increading the
likelihood that the galaxies in the sample are truly edge-on. We have also
concentrated the sample on galaxies with low apparent surface brightness, in
order to increase the representation of intrinisically low surface brightness
galaxies. Finally, the sample was chosen to have no apprarent bulges or optical
warps so that the galaxies represent undisturbed, ``pure disk'' systems. The
resulting sample forms the basis for a much larger spectroscopic study designed
to place constraints on the physical quantities and processes which shape disk
galaxies. The imaging data presented in this paper has been painstakingly
reduced and calibrated to allow accurate surface photometry of features as
faint as 30 mag/sqr-arcsec in B and 29 mag/sqr-arcsec in R on scales larger
than 10 arcsec. Due to limitations in sky subtraction and flat fielding, the
infrared data can reach only to 22.5 mag/sqr-arcsec in K_s on comparable
scales. As part of this work, we have developed a new method for quantifying
the reliability of surface photometry, which provides useful diagnostics for
the presence of scattered light, optical emission from infrared cirrus, and
other sources of non-uniform sky backgrounds.Comment: scheduled to appear in the Astronomical Journal, LaTeX, 36 pages
including 7 pages of figures (fig 1-2,4). A low resolution version of Figure
3 is included in JPEG format; contours are seriously degraded. A full
resolution Postscript version of Figure 3 (10.6Mb,gzipped) is available
through anonymous ftp at
ftp://ftp.astro.washington.edu/pub/users/jd/FGC/dalcanton.f3.ps.g
The Hipparcos Transit Data: What, why and how?
The Hipparcos Transit Data are a collection of partially reduced, fully
calibrated observations of (mostly) double and multiple stars obtained with the
ESA Hipparcos astrometry satellite. The data are publicly available, as part of
the CD-ROM set distributed with the Hipparcos and Tycho Catalogues (ESA
SP--1200, 1997), for about a third of the Hipparcos Catalogue entries including
all confirmed or suspected non-single stars. The Transit Data consist of signal
modulation parameters derived from the individual transits of the targets
across the Hipparcos focal grid. The Transit Data permit re-reduction of the
satellite data for individual objects, using arbitrarily complex object models
in which time-variable photometric as well as geometric characteristics may be
taken into account. We describe the structure and contents of the Transit Data
files and give examples of how the data can be used. Some of the applications
use standard astronomical software: Difmap or AIPS for aperture synthesis
imaging, and GaussFit for detailed model fitting. Fortran code converting the
data into formats suitable for these application programs has been made public
in order to encourage and facilitate the use of Hipparcos Transit Data.Comment: A&AS, accepted for publication, 17 pages, 9 figures, 1 Table,
Software available via http://www.astro.lu.se/~lennart/TD/index.html, Figures
4, 5, 6 and 7 need to copied separately, A complete postscript file can be
found at http://www.astro.lu.se/~lennart/TD/ds1699.ps.g
A Sensitive Search for Variability in Late L Dwarfs: The Quest for Weather
We have conducted a photometric monitoring program of three field late L brown dwarfs (DENIS-P J0255-4700, 2MASS J0908+5032, and 2MASS J2244+2043) looking for evidence of nonaxisymmetric structure or temporal variability in their photospheres. The observations were performed using Spitzer IRAC 4.5 and 8 ÎŒm bandpasses and were designed to cover at least one rotational period of each object; 1 Ï rms uncertainties of less than 3 mmag at 4.5 ÎŒm and around 9 mmag at 8 ÎŒm were achieved. Two out of the three objects studied exhibit some modulation in their light curves at 4.5 ÎŒmâbut not 8 ÎŒmâwith periods of 7.4 hr (DENIS 0255) and 4.6 hr (2MA 2244) and peak-to-peak amplitudes of 10 and 8 mmag. Although the lack of detectable 8 ÎŒm variation suggests an instrumental origin for the detected variations, the data may nevertheless still be consistent with intrinsic variability, since the shorter wavelength IRAC bandpasses probe more deeply into late L dwarf atmospheres than the longer wavelengths. A cloud feature occupying a small percentage (1%-2%) of the visible hemisphere could account for the observed amplitude of variation. If, instead, the variability is indeed instrumental in origin, then our nonvariable L dwarfs could be either completely covered with clouds or objects whose clouds are smaller and uniformly distributed. Such scenarios would lead to very small photometric variations. Follow-up IRAC photometry at 3.6 and 5.8 ÎŒm bandpasses should distinguish between the two cases. In any event, the present observations provide the most sensitive search to date for structure in the photospheres of late L dwarfs at mid-IR wavelengths, and our photometry provides stringent upper limits to the extent to which the photospheres of these transition L dwarfs are structured
ISO continuum observations of quasars at z=1-4 I.Spectral energy distributions of quasars from the UV to far-infrared
Eight luminous quasars with at z = 1.4 - 3.7 have been
observed in the mid- and far-infrared using ISO. All the quasars have been
detected in the mid-infrared bands of ISOCAM, while no far-infrared detections
have been made with ISOPHOT. Supplementing ISO observations with photometry in
the optical and near-infrared made from the ground mostly within 17 months
after the ISO observations, SEDs (Spectral Energy Distributions) from the UV to
far-infrared have been obtained. SEDs (Spectral Energy Distributions) from the
UV to far-infrared have been obtained while supplementing ISO observations with
photometry in the optical and near-infrared made from the ground within 17
months. The SEDs are compared with the MED (Mean spectral Energy Distributions)
of low-redshift quasars with . It is shown that our
far-infrared observations were limited by confusion noise due to crowded
sources.Comment: 9 pages, 3 figures: accepted for publication in Astronomy and
Astrophysic
Recommended from our members
A Photometric Redshift of z ~ 9.4 for GRB 090429B
Gamma-ray bursts (GRBs) serve as powerful probes of the early universe, with their luminous afterglows revealing the locations and physical properties of star-forming galaxies at the highest redshifts, and potentially locating first-generation (Population III) stars. Since GRB afterglows have intrinsically very simple spectra, they allow robust redshifts from low signal-to-noise spectroscopy, or photometry. Here we present a photometric redshift of z ~ 9.4 for the Swift detected GRB 090429B based on deep observations with Gemini-North, the Very Large Telescope, and the GRB Optical and Near-infrared Detector. Assuming a Small Magellanic Cloud dust law (which has been found in a majority of GRB sight lines), the 90% likelihood range for the redshift is 9.06 7. The non-detection of the host galaxy to deep limits (Y(AB) ~ 28, which would correspond roughly to 0.001L* at z = 1) in our late-time optical and infrared observations with the Hubble Space Telescope strongly supports the extreme-redshift origin of GRB 090429B, since we would expect to have detected any low-z galaxy, even if it were highly dusty. Finally, the energetics of GRB 090429B are comparable to those of other GRBs and suggest that its progenitor is not greatly different from those of lower redshift bursts
GLIMPSE: I. A SIRTF Legacy Project to Map the Inner Galaxy
GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire), a SIRTF
Legacy Science Program, will be a fully sampled, confusion-limited infrared
survey of the inner two-thirds of the Galactic disk with a pixel resolution of
\~1.2" using the Infrared Array Camera (IRAC) at 3.6, 4.5, 5.8, and 8.0
microns. The survey will cover Galactic latitudes |b| <1 degree and longitudes
|l|=10 to 65 degrees (both sides of the Galactic center). The survey area
contains the outer ends of the Galactic bar, the Galactic molecular ring, and
the inner spiral arms. The GLIMPSE team will process these data to produce a
point source catalog, a point source data archive, and a set of mosaicked
images. We summarize our observing strategy, give details of our data products,
and summarize some of the principal science questions that will be addressed
using GLIMPSE data. Up-to-date documentation, survey progress, and information
on complementary datasets are available on the GLIMPSE web site:
www.astro.wisc.edu/glimpse.Comment: Description of GLIMPSE, a SIRTF Legacy project (Aug 2003 PASP, in
press). Paper with full res.color figures at
http://www.astro.wisc.edu/glimpse/glimpsepubs.htm
Revealing the Nature of Algol Disks through Optical and UV Spectroscopy, Synthetic Spectra, and Tomography of TT Hydrae
We have developed a systematic procedure to study the disks in Algol-type
binaries using spectroscopic analysis, synthetic spectra, and tomography. We
analyzed 119 H-alpha spectra of TT Hya, an Algol-type eclipsing interacting
binary, collected from 1985-2001. The new radial velocities enabled us to
derive reliable orbital elements, including a small non-zero eccentricity, and
to improve the accuracy of the absolute dimensions of the system. High
resolution IUE spectra were also analyzed to study the formation of the
ultraviolet lines and continuum. Synthetic spectra of the iron curtain using
our new shellspec program enabled us to derive a characteristic disk
temperature of 7000K. We have demonstrated that the UV emission lines seen
during total primary eclipse cannot originate from the accretion disk, but most
likely arise from a hotter disk-stream interaction region.
The synthetic spectra of the stars, disk, and stream allowed us to derive a
lower limit to the mass transfer rate of 2e-10 solar masses per year. Doppler
tomography of the observed H-alpha profiles revealed a distinct accretion disk.
The difference spectra produced by subtracting the synthetic spectra of the
stars resulted in an image of the disk, which virtually disappeared once the
composite synthetic spectra of the stars and disk were used to calculate the
difference spectra. An intensity enhancement of the resulting tomogram revealed
images of the gas stream and an emission arc. We successfully modeled the gas
stream using shellspec and associated the emission arc with an asymmetry in the
accretion disk.Comment: 46 pages, 15 figures, 6 tables, accepted by Ap
The Ultraviolet Imaging Telescope: Instrument and Data Characteristics
The Ultraviolet Imaging Telescope (UIT) was flown as part of the Astro
observatory on the Space Shuttle Columbia in December 1990 and again on the
Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300 Angstroms) images
of a variety of astronomical objects, with a 40 arcmin field of view and a
resolution of about 3 arcsec, were recorded on photographic film. The data
recorded during the first flight are available to the astronomical community
through the National Space Science Data Center (NSSDC); the data recorded
during the second flight will soon be available as well. This paper discusses
in detail the design, operation, data reduction, and calibration of UIT,
providing the user of the data with information for understanding and using the
data. It also provides guidelines for analyzing other astronomical imagery made
with image intensifiers and photographic film.Comment: 44 pages, LaTeX, AAS preprint style and EPSF macros, accepted by PAS
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