5,602 research outputs found
Spectrophotometry of nearby field galaxies: the data
We have obtained integrated and nuclear spectra, as well as U, B, R surface
photometry, for a representative sample of 196 nearby galaxies. These galaxies
span the entire Hubble sequence in morphological type, as well as a wide range
of luminosities (M_B=-14 to -22). Here we present the spectrophotometry for
these galaxies. The selection of the sample and the U, B, R surface photometry
is described in a companion paper (Paper I). Our goals for the project include
measuring the current star formation rates and metallicities of these galaxies,
and elucidating their star formation histories, as a function of luminosity and
morphology. We thereby extend the work of Kennicutt (1992a) to lower luminosity
systems. We anticipate that our study will be useful as a benchmark for studies
of galaxies at high redshift.
We describe the observing, data reduction and calibration techniques, and
demonstrate that our spectrophotometry agrees well with that of Kennicutt. The
spectra span the range 3550--7250 A at a resolution (FWHM) of ~6 A, and have an
overall relative spectrophotometric accuracy of +/- 6 per cent. We present a
spectrophotometric atlas of integrated and nuclear rest-frame spectra, as well
as tables of equivalent widths and synthetic colors.
We study the correlations of galaxy properties determined from the spectra
and images. Our findings include: (1) galaxies of a given morphological class
display a wide range of continuum shapes and emission line strengths if a broad
range of luminosities are considered, (2) emission line strengths tend to in-
crease and continua tend to get bluer as the luminosity decreases, and (3) the
scatter on the general correlation between nuclear and integrated H_alpha
emission line strengths is large.Comment: Accepted for publication in ApJS (scheduled for Vol.127, 2000 March);
63 pages, LateX, 9 figures and 6 tables included, a spectrophotometric atlas
is provided as GIF images, fig 1 as a JPEG image, in a single tar-file; a
full 600 dpi version is available at http://www.astro.rug.nl/~nfgs
Setting UBVRI Photometric Zero-Points Using Sloan Digital Sky Survey ugriz Magnitudes
We discuss the use of Sloan Digital Sky Survey (SDSS) ugriz point-spread
function (PSF) photometry for setting the zero points of UBVRI CCD images. From
a comparison with the Landolt (1992) standards and our own photometry we find
that there is a fairly abrupt change in B, V, R, & I zero points around g, r, i
~ 14.5, and in the U zero point at u ~ 16. These changes correspond to where
there is significant interpolation due to saturation in the SDSS PSF fluxes.
There also seems to be another, much smaller systematic effect for stars with
g, r > 19.5. The latter effect is consistent with a small Malmquist bias.
Because of the difficulties with PSF fluxes of brighter stars, we recommend
that comparisons of ugriz and UBVRI photometry should only be made for
unsaturated stars with g, r and i in the range 14.5 - 19.5, and u in the range
16 - 19.5. We give a prescription for setting the UBVRI zero points for CCD
images, and general equations for transforming from ugriz to UBVRI.Comment: 13 pages. 6 figures. Accepted for publication in the Astronomical
Journa
A Photometric Technique to Search for Be Stars in Open Clusters
We describe a technique to identify Be stars in open clusters using Stromgren
b, y, and narrow-band Halpha photometry. We first identify the B-type stars of
the cluster using a theoretical isochrone fit to the (b-y, y) color-magnitude
diagram. The strongest Be stars are easily identified in a (b-y, y-Halpha)
color-color diagram, but those with weaker Halpha emission (classified as
possible Be star detections) may be confused with evolved or foreground stars.
Here we present such photometry plus Halpha spectroscopy of members of the
cluster NGC 3766 to demonstrate the accuracy of our technique. Statistical
results on the relative numbers of Be and B-type stars in additional clusters
will be presented in a future paper.Comment: 15 pages, 6 figures, 1 table. Accepted by Ap
The Stellar Populations in the Outer Regions of M33. I. Metallicity Distribution Function
We present deep CCD photometry in the VI passbands using the WIYN 3.5m
telescope of a field located approximately 20' southeast of the center of M33;
this field includes the region studied by Mould & Kristian in their 1986 paper.
The color-magnitude diagram (CMD) extends to I~25 and shows a prominent red
giant branch (RGB), along with significant numbers of asymptotic giant branch
and young main sequence stars. The red clump of core helium burning stars is
also discernable near the limit of our CMD. The I-band apparent magnitude of
the red giant branch tip implies a distance modulus of (m-M)_I = 24.77 +/-
0.06, which combined with an adopted reddening of E(V-I)=0.06 +/- 0.02 yields
an absolute modulus of (m-M)_0 = 24.69 +/- 0.07 (867 +/- 28 kpc) for M33. Over
the range of deprojected radii covered by our field (~8.5 to ~12.5 kpc), we
find a significant age gradient with an upper limit of ~1 Gyr (~0.25 Gyr/kpc).
Comparison of the RGB photometry to empirical giant branch sequences for
Galactic globulars allows us to use the dereddened color of these stars to
construct a metallicity distribution function (MDF). The primary peak in the
MDF is at a metallicity of [Fe/H] ~ -1.0 with a tail to lower abundances. The
peak does show radial variation with a slope of d[Fe/H]/dR_{deproj} = -0.06 +/-
0.01 dex/kpc. This gradient is consistent with the variation seen in the inner
disk regions of M33. As such, we conclude that the vast majority of stars in
this field belong to the disk of M33, not the halo as previously thought.Comment: 34 pages, 13 figures, accepted to The Astronomical Journal, July
2004, high resolution version available at
ftp://www.astro.ufl.edu/pub/ata/sarajedini_m33.pd
A Possible Massive Asteroid Belt Around zeta Lep
We have used the Keck I telescope to image at 11.7 microns and 17.9 microns
the dust emission around zeta Lep, a main sequence A-type star at 21.5 pc from
the Sun with an infrared excess. The excess is at most marginally resolved at
17.9 microns. The dust distance from the star is probably less than or equal to
6 AU, although some dust may extend to 9 AU. The mass of observed dust is
\~10^22 g. Since the lifetime of dust particles is about 10,000 years because
of the Poytning-Robertson effect, we robustly estimate at least 4 10^26 g must
reside in parent bodies which may be asteroids if the system is in a steady
state and has an age of ~300 Myr. This mass is approximately 200 times that
contained within the main asteroid belt in our solar system.Comment: 12 pages, 3 figures, ApJL in pres
Including Systematic Uncertainties in Confidence Interval Construction for Poisson Statistics
One way to incorporate systematic uncertainties into the calculation of
confidence intervals is by integrating over probability density functions
parametrizing the uncertainties. In this note we present a development of this
method which takes into account uncertainties in the prediction of background
processes, uncertainties in the signal detection efficiency and background
efficiency and allows for a correlation between the signal and background
detection efficiencies. We implement this method with the Feldman & Cousins
unified approach with and without conditioning. We present studies of coverage
for the Feldman & Cousins and Neyman ordering schemes. In particular, we
present two different types of coverage tests for the case where systematic
uncertainties are included. To illustrate the method we show the relative
effect of including systematic uncertainties the case of dark matter search as
performed by modern neutrino tel escopes.Comment: 23 pages, 10 figures, replaced to match published versio
Stellar Populations of the Sagittarius Dwarf Irregular Galaxy
We present deep BVRI CCD photometry of the stars in the dwarf irregular
galaxy SagDIG. The color-magnitude diagrams of the measured stars in SagDIG
show a blue plume which consists mostly of young stellar populations, and a
well-defined red giant branch (RGB). The foreground reddening of SagDIG is
estimated to be E(B-V)=0.06. The tip of the RGB is found to be at
I_(TRGB)=21.55 +/- 0.10 mag. From this the distance to this galaxy is estimated
to be d = 1.18 +/- 0.10 Mpc. This result, combined with its velocity
information, shows that it is a member of the Local Group. The mean metallicity
of the red giant branch is estimated to be [Fe/H] < -2.2 dex. This shows that
SagDIG is one of the most metal-poor galaxies. Total magnitudes of SagDIG (<
r_H (= 107 arcsec)) are derived to be B^T=13.99 mag, V^T=13.58 mag, R^T=13.19
mag, and I^T=12.88 mag, and the corresponding absolute magnitudes are
M_B=-11.62 mag, M_V=-11.97 mag, M_R=-12.33 mag, and M_I=-12.60 mag. Surface
brightness profiles of the central part of SagDIG are approximately fit by a
King model with a core concentration parameter c = log (r_t / r_c) ~ 0.6, and
those of the outer part follow an exponential law with a scale length of 37
arcsec. The central surface brightness is measured to be mu_B (0) = 24.21 mag
arcsec^(-2) and mu_V (0) =23.91 mag arcsec^(-2). The magnitudes and colors of
the brightest blue and red stars in SagDIG (BSG and RSG) are measured to be,
respectively, _BSG = 19.89 +/- 0.13 mag, _BSG = 0.08 +/- 0.07
mag, _RSG = 20.39 +/- 0.10 mag, and _RSG = 1.29 +/- 0.12 mag.
The corresponding absolute magnitudes are derived to be _BSG = -5.66
mag and _RSG = -5.16 mag, which are about one magnitude fainter than
those expected from conventional correlations with galaxy luminosity.Comment: 16 pages(AASLaTeX), 10 Postscript figures, Accepted for publication
in Astronomical Journal, 200
New optical and near-infrared Surface Brightness Fluctuations models. A primary distance indicator ranging from Globular Clusters to distant galaxies?
We present new theoretical models for Surface Brightness Fluctuations (SBF)
both for optical and near-infrared bands in standard ground-based and Hubble
Space Telescope filter systems. Simple Stellar Population simulations are
adopted. Models cover the age and metallicity ranges from to and
from to 0.04 respectively. Effects due to the variation of the
Initial Mass Function and the stellar color-temperature relations are explored.
Particular attention is devoted to very bright stars in the color-magnitude
diagram and to investigate the effects of mass loss along the Red Giant Branch
(RGB) and the Asymptotic Giant Branch (AGB). It is found that and bands
SBF amplitudes are powerful diagnostics for the morphology of the Horizontal
Branch and the Post-AGB stars population. We point out that a careful treatment
of mass loss process along the RGB and AGB is fundamental in determining
reliable SBF evaluations. The SBF measurements are used to give robust
constraints on the evolution of AGB stars, suggesting that mass loss activity
on AGB stars should be twice more efficient than on the RGB stars. Our models
are able to reproduce the absolute SBF magnitudes of the Galactic Globular
Clusters and of galaxies, and their integrated colors. New calibrations of
absolute SBF magnitude in , , , and photometric filters are
provided, which appear reliable enough to directly gauge distances bypassing
other distance indicators. The SBF technique is also used as stellar population
tracer to derive age and metallicity of a selected sample of galaxies of known
distances. Finally, {\it SBF color} versus {\it integrated color} diagrams are
proposed as particularly useful in removing the well known {\it age-metallicity
degeneracy} affecting our knowledge of remote stellar systems.Comment: AJ accepted, 46 pages, 21 figures, 10 tables, uses aastex.cl
Spectroscopy and Time Variability of Absorption Lines in the Direction of the Vela Supernova Remnant
We present high resolution (R~75,000), high signal-to-noise (S/N~100) Ca II
3933.663 and Na I 5889.951, 5895.924 spectra of 68
stars in the direction of the Vela supernova remnant. The spectra comprise the
most complete high resolution, high S/N, optical survey of early type stars in
this region of the sky. A subset of the sight lines has been observed at
multiple epochs, 1993/1994 and 1996. Of the thirteen stars observed twice,
seven have spectra revealing changes in the equivalent width and/or velocity
structure of lines, most of which arise from remnant gas. Such time variability
has been reported previously for the sight lines towards HD 72089 and HD 72997
by Danks & Sembach (1995) and for HD 72127 by Hobbs et al. (1991). We have
confirmed the ongoing time variability of these spectra and present new
evidence of variability in the spectra of HD 73658, HD 74455, HD 75309 and HD
75821. We have tabulated Na I and Ca II absorption line information for the
sight lines in our sample to serve as a benchmark for further investigations of
the dynamics and evolution of the Vela SNR.Comment: 8 pages of text, 4 tables, 16 pages of figures Accepted and to be
published in ApJ
The Palomar Testbed Interferometer Calibrator Catalog
The Palomar Testbed Interferometer (PTI) archive of observations between 1998
and 2005 is examined for objects appropriate for calibration of optical
long-baseline interferometer observations - stars that are predictably
point-like and single. Approximately 1,400 nights of data on 1,800 objects were
examined for this investigation. We compare those observations to an
intensively studied object that is a suitable calibrator, HD217014, and
statistically compare each candidate calibrator to that object by computing
both a Mahalanobis distance and a Principal Component Analysis. Our hypothesis
is that the frequency distribution of visibility data associated with
calibrator stars differs from non-calibrator stars such as binary stars.
Spectroscopic binaries resolved by PTI, objects known to be unsuitable for
calibrator use, are similarly tested to establish detection limits of this
approach. From this investigation, we find more than 350 observed stars
suitable for use as calibrators (with an additional being
rejected), corresponding to sky coverage for PTI. This approach
is noteworthy in that it rigorously establishes calibration sources through a
traceable, empirical methodology, leveraging the predictions of spectral energy
distribution modeling but also verifying it with the rich body of PTI's on-sky
observations.Comment: 100 pages, 7 figures, 7 tables; to appear in the May 2008ApJS, v176n
- …