We present the photometric calibration technique for the Digitized Second Palomar Observatory Sky Survey (DPOSS), used to create seamless catalogs of calibrated objects over large sky areas. After ...applying a correction for telescope vignetting, the extensive plate overlap regions are used to transform sets of plates onto a common instrumental photometric system. Photometric transformations to the Gunn gri system for each plate, for stars and galaxies, are derived using these contiguous stitched areas and an extensive CCD imaging library obtained for this purpose. We discuss the resulting photometric accuracy, survey depth, and possible systematic errors.
Exploration of the time variability on the sky over a broad range of flux levels and wavelengths is rapidly becoming a new frontier of astronomical research. We describe here briefly the ...Palomar-QUEST survey being carried out from the Samuel Oschin 48-inch Schmidt telescope at Palomar. The following features make the survey an attractive candidate for studying time variability: anticipated survey area of 12,000 - 15,000 sq. degrees in the drift scan mode, point source depth of 21st mag. in I under good conditions, near simultaneous observations in four filters, and at least four passes per year at each location covered. The survey will yield a large number of transients and highly variable sources in the near future and in that sense is a prototype of LSST and Pan-STARRS. We briefly outline our strategy for searching such objects and the proposed pipeline for detecting transients in real-time.
AIP Conf.Proc.662:56-58,2003 We report the discovery of the optical and radio afterglow of GRB 010921, the
first gamma-ray burst afterglow to be found from a localization by the High
Energy Transient ...Explorer (HETE) satellite. We present optical spectroscopy of
the host galaxy which we find to be a dusty and apparently normal star-forming
galaxy at z = 0.451. The unusually steep optical spectral slope of the
afterglow can be explained by heavy extinction, A_V > 0.5 mag, along the line
of sight to the GRB. Dust with similar A_V for the the host galaxy as a whole
appears to be required by the measurement of a Balmer decrement in the spectrum
of the host galaxy. Thanks to the low redshift, continued observations of the
afterglow will enable the strongest constraints, to date, on the existence of a
possible underlying supernova.
Of all the well localized gamma-ray bursts, GRB 000911 has the longest
duration (T_90 ~ 500 s), and ranks in the top 1% of BATSE bursts for fluence.
Here, we report the discovery of the afterglow of ...this unique burst. In order
to simultaneously fit our radio and optical observations, we are required to
invoke a model involving an hard electron distribution, p ~ 1.5 and a jet-break
time less than 1.5 day. A spectrum of the host galaxy taken 111 days after the
burst reveals a single emission line, interpreted as OII at a redshift z =
1.0585, and a continuum break which we interpret as the Balmer limit at this
redshift. Despite the long T_90, the afterglow of GRB 000911 is not unusual in
any other way when compared to the set of afterglows studied to date. We
conclude that the duration of the GRB plays little part in determining the
physics of the afterglow.
With the recent release of large (i.e., > hundred million objects), well-calibrated photometric surveys, such as DPOSS, 2MASS, and SDSS, spectroscopic identification of important targets is no longer ...a simple issue. In order to enhance the returns from a spectroscopic survey, candidate sources are often preferentially selected to be of interest, such as brown dwarfs or high redshift quasars. This approach, while useful for targeted projects, risks missing new or unusual species. We have, as a result, taken the alternative path of spectroscopically identifying interesting sources with the sole criterion being that they are in low density areas of the g - r and r - i color-space defined by the DPOSS survey. In this paper, we present three peculiar broad absorption line quasars that were discovered during this spectroscopic survey, demonstrating the efficacy of this approach. PSS J0052+2405 is an Iron LoBAL quasar at a redshift z = 2.4512 with very broad absorption from many species. PSS J0141+3334 is a reddened LoBAL quasar at z = 3.005 with no obvious emission lines. PSS J1537+1227 is a Iron LoBAL at a redshift of z = 1.212 with strong narrow Mgii and Feii emission. Follow-up high resolution spectroscopy of these three quasars promises to improve our understanding of BAL quasars. The sensitivity of particular parameter spaces, in this case a two-color space, to the redshift of these three sources is dramatic, raising questions about traditional techniques of defining quasar populations for statistical analysis.
Systematic exploration of the observable parameter space, covered by large digital sky surveys spanning a range of wavelengths, will be one of the primary modes of research with a Virtual Observatory ...(VO). This will include searches for rare, unusual, or even previously unknown types of astronomical objects and phenomena, e.g. as outliers in some parameter space of measured properties, both in the catalog and image domains. Examples from current surveys include high-redshift quasars, type-2 quasars, brown dwarfs, and a small number of objects with puzzling spectra. Opening of the time domain will be especially interesting in this regard. Data-mining tools such as unsupervised clustering techniques will be essential in this task, and should become an important part of the VO toolkit.
Studies of the cosmic gamma-ray bursts (GRBs) and their host galaxies are starting to provide interesting or even unique new insights in observational cosmology. GRBs represent a new way of ...identifying a population of star-forming galaxies at cosmological redshifts. GRB hosts are broadly similar to the normal field galaxy populations at comparable redshifts and magnitudes, and indicate at most a mild luminosity evolution out to z ~ 1.5 - 2. GRB optical afterglows seen in absorption provide a powerful new probe of the ISM in dense, central regions of their host galaxies, complementary to the traditional studies using QSO absorbers. Some GRB hosts are heavily obscured, and provide a new way to select a population of cosmological sub-mm sources, and a novel constraint on the total obscured fraction of star formation over the history of the universe. Finally, detection of GRB afterglows at z > 6 may provide a unique way to probe the primordial star formation, massive IMF, early IGM, and chemical enrichment at the end of the cosmic reionization era.
One of the new frontiers of astronomical research is the exploration of time variability on the sky at different wavelengths and flux levels. We have carried out a pilot project using DPOSS data to ...study strong variables and transients, and are now extending it to the new Palomar-QUEST synoptic sky survey. We report on our early findings and outline the methodology to be implemented in preparation for a real-time transient detection pipeline. In addition to large numbers of known types of highly variable sources (e.g., SNe, CVs, OVV QSOs, etc.), we expect to find numerous transients whose nature may be established by a rapid follow-up. Whereas we will make all detected variables publicly available through the web, we anticipate that email alerts would be issued in the real time for a subset of events deemed to be the most interesting. This real-time process entails many challenges, in an effort to maintain a high completeness while keeping the contamination low. We will utilize distributed Grid services developed by the GRIST project, and implement a variety of advanced statistical and machine learning techniques.
We review some of the scientific opportunities and technical challenges posed by the exploration of the large digital sky surveys, in the context of a Virtual Observatory (VO). The VO paradigm will ...profoundly change the way observational astronomy is done. Clustering analysis techniques can be used to discover samples of rare, unusual, or even previously unknown types of astronomical objects and phenomena. Exploration of the previously poorly probed portions of the observable parameter space are especially promising. We illustrate some of the possible types of studies with examples drawn from DPOSS; much more complex and interesting applications are forthcoming. Development of the new tools needed for an efficient exploration of these vast data sets requires a synergy between astronomy and information sciences, with great potential returns for both fields.
Studies of the cosmic gamma-ray bursts (GRBs) and their host galaxies are now starting to provide interesting or even unique new insights in observational cosmology. Observed GRB host galaxies have a ...median magnitude R ~ 25 mag, and show a range of luminosities, morphologies, and star formation rates, with a median redshift z ~ 1. They represent a new way of identifying a population of star-forming galaxies at cosmological redshifts, which is mostly independent of the traditional selection methods. They seem to be broadly similar to the normal field galaxy populations at comparable redshifts and magnitudes, and indicate at most a mild luminosity evolution over the redshift range they probe. Studies of GRB optical afterglows seen in absorption provide a powerful new probe of the ISM in dense, central regions of their host galaxies, which is complementary to the traditional studies using QSO absorption line systems. Some GRB hosts are heavily obscured, and provide a new way to select a population of cosmological sub-mm sources. A census of detected optical tranistents may provide an important new way to constrain the total obscured fraction of star formation over the history of the universe. Finally, detection of GRB afterglows at high redshifts (z > 6) may provide a unique way to probe the primordial star formation, massive IMF, early IGM, and chemical enrichment at the end of the cosmic reionization era.
