11 research outputs found
A Multiwavelength Investigation of Unidentified EGRET Sources
Statistical studies indicate that the 271 point sources of high-energy gamma
rays belong to two groups: a Galactic population and an isotropic extragalactic
population. Many unidentified extragalactic sources are certainly blazars, and
it is the intention of this work to uncover gamma-ray blazars missed by
previous attempts. Until recently, searches for blazar counterparts to
unidentified EGRET sources have focused on finding AGN that have 5-GHz radio
flux densities S_5 near or above 1 Jy. However, the recent blazar
identification of 3EG J2006-2321 (S_5 = 260 mJy) and other work suggest that
careful studies of weaker flat-spectrum sources may be fruitful. In this
spirit, error circles of 4 high-latitude unidentified EGRET sources have been
searched for 5-GHz sources. The gamma-ray sources are 3EG J1133+0033, 3EG
J1212+2304, 3EG J1222+2315, and 3EG J1227+4302. Within the error contours of
each of the four sources are found 6 radio candidates; by observing the
positions of the radio sources with the 0.81-m Tenagra II telescope it is
determined that 14 of these 24 radio sources have optical counterparts with R <
22. Eight of these from two different EGRET sources have been observed in the
B, V, and R bands in more than one epoch and the analysis of these data is
ongoing. Any sources that are found to be variable will be the objects of
multi-epoch polarimetry studies.Comment: 6 pages, 2 tables. To appear in Astrophysics & Space Scienc
Optical photometry of GM Cep: evidence for UXor type of variability
Results from optical photometric observations of the pre-main sequence star
GM Cep are reported in the paper. The star is located in the field of the young
open cluster Trumpler 37 - a region of active star formation. GM Cep shows a
large amplitude rapid variability interpreted as a possible outburst from EXor
type in previous studies. Our data from BVRI CCD photometric observations of
the star are collected from June 2008 to February 2011 in Rozhen observatory
(Bulgaria) and Skinakas observatory (Crete, Greece). A sequence of sixteen
comparison stars in the field of GM Cep was calibrated in the BVRI bands. Our
photometric data for a 2.5 years period show a high amplitude variations (Delta
V ~ 2.3m) and two deep minimums in brightness are observed. The analysis of
collected multicolor photometric data shows the typical of UX Ori variables a
color reversal during the minimums in brightness. On the other hand, high
amplitude rapid variations in brightness typical for the Classical T Tauri
stars also present on the light curve of GM Cep. Comparing our results with
results published in the literature, we conclude that changes in brightness are
caused by superposition of both: (1) magnetically channeled accretion from the
circumstellar disk, and (2) occultation from circumstellar clouds of dust or
from features of a circumstellar disk.Comment: 7 pages, 3 figures, accepted for publication in Ap&S
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc