11 research outputs found
The Fall and the Rise of X-rays from Dwarf Novae in Outburst: RXTE Observations of VW Hydri and WW Ceti
In a dwarf nova, the accretion disk around the white dwarf is a source of
ultraviolet, optical, and infrared photons, but is never hot enough to emit
X-rays. Observed X-rays instead originate from the boundary layer between the
disk and the white dwarf. As the disk switches between quiescence and outburst
states, the 2-10 keV X-ray flux is usually seen to be anti-correlated with the
optical brightness. Here we present RXTE monitoring observations of two dwarf
novae, VW Hyi and WW Cet, confirming the optical/X-ray anti-correlation in
these two systems. However, we do not detect any episodes of increased hard
X-ray flux on the rise (out of two possible chances for WW Cet) or the decline
(two for WW Cet and one for VW Hyi) from outburst, attributes that are clearly
established in SS Cyg. The addition of these data to the existing literature
establishes the fact that the behavior of SS Cyg is the exception, rather than
the archetype as is often assumed. We speculate on the origin of the diversity
of behaviors exhibited by dwarf novae, focusing on the role played by the white
dwarf mass.Comment: PASP, in press (18 pages including 3 figures
Galaxy pairs in the Sloan Digital Sky Survey – X. Does gas content alter star formation rate enhancement in galaxy interactions?
New spectral line observations, obtained with the Jansky Very Large Array (VLA), of a sample of 34 galaxies in 17 close pairs are presented in this paper. The sample of galaxy pairs is selected to contain galaxies in close, major interactions (i.e. projected separations 3σ. We compare the H i gas fraction of the galaxies with the triggered star formation present in that galaxy. When compared to the star formation rates (SFRs) of non-pair galaxies matched in mass, redshift, and local environment, we find that the star formation enhancement is weakly positively correlated (∼2.5σ) with H i gas fraction. In order to help understand the physical mechanisms driving this weak correlation, we also present results from a small suite of binary galaxy merger simulations with varying gas fractions. The simulated galaxies indicate that larger initial gas fractions are associated with lower levels of interaction-triggered star formation (relative to an identical galaxy in isolation), but also show that high gas fraction galaxies have higher absolute SFRs prior to an interaction. We show that when interaction-driven SFR enhancements are calculated relative to a galaxy with an average gas fraction for its stellar mass, the relationship between SFR and initial gas fraction dominates over the SFR enhancements driven by the interaction. Simulated galaxy interactions that are matched in stellar mass but not in gas fraction, like our VLA sample, yield the same general positive correlation between SFR enhancement and gas fraction that we observe
The arecibo legacy fast ALFA survey: The ALFALFA extragalactic HI source catalog
We present the catalog of ∼31,500 extragalactic H i line sources detected by the completed Arecibo Legacy Fast ALFA (ALFALFA) survey out to z 6.5) detections and ones of lower quality that coincide in both position and recessional velocity with galaxies of known redshift. We review the observing technique, data reduction pipeline, and catalog construction process, focusing on details of particular relevance to understanding the catalog's compiled parameters. We further describe and make available the digital H i line spectra associated with the cataloged sources. In addition to the extragalactic H i line detections, we report nine confirmed OH megamasers (OHMs) and 10 OHM candidates at 0.16 < z < 0.22 whose OH line signals are redshifted into the ALFALFA frequency band. Because of complexities in data collection and processing associated with the use of a feed-horn array on a complex single-dish antenna in the terrestrial radio frequency interference environment, we also present a list of suggestions and caveats for consideration by users of the ALFALFA extragalactic catalog for future scientific investigations.© 2018. The American Astronomical Society. All rights reserved.The authors acknowledge the work of the entire ALFALFA collaboration who have contributed to the many aspects of the survey over the years. The ALFALFA team at Cornell has been supported by NSF grants AST-0607007, AST-1107390, and AST-1714828 and grants from the Brinson Foundation. Participation of the Undergraduate ALFALFA Team has been made possible by NSF grants AST-0724918, AST-0725267, AST-0725380, AST-0902211, AST-0903394, AST-1211005, AST-1637339, AST-1637271, AST-1637299, AST-1637262, and AST-1637276. EAKA is supported by the WISE research program, which is financed by the Netherlands Organisation for Scientific Research (NWO). BRK acknowledges the National Radio Astronomy Observatory (NRAO). The NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. MGJ acknowledges support from grant AYA2015-65973-C3-1-R (MINECO/FEDER, UE). We thank Dmitry Makarov for comments and suggestions on cross-identifications.
This work is based on observations made with the Arecibo Observatory. The Arecibo Observatory has been operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968) and in alliance with Ana G. Mendez-Universidad Metropolitana and the Universities Space Research Association. We thank the staff of the Arecibo Observatory, especially Phil Perillat, Ganesh Rajagopalan, Arun Venkataraman, Hector Hernandez, and the telescope operations group for their outstanding support of the ALFALFA survey program.
We acknowledge the use of NASA's SkyView facility (http://skyview.gsfc.nasa.gov), located at NASA Goddard Space Flight Center, and the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. The Second Palomar Observatory Sky Survey (POSS-II) was made by the California Institute of Technology with funds from the National Science Foundation, the National Geographic Society, the Sloan Foundation, the Samuel Oschin Foundation, and the Eastman Kodak Corporation.
This research used data from the Sloan Digital Sky Survey. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England
Unmet Need for Total Joint Arthroplasty in Medicaid Beneficiaries After Affordable Care Act Expansion
The Arecibo Legacy Fast ALFA Survey:The ALFALFA Extragalactic HI Source Catalog
We present the catalog of ~31500 extragalactic HI line sources detected by
the completed ALFALFA survey out to z < 0.06 including both high
signal-to-noise ratio (> 6.5) detections and ones of lower quality which
coincide in both position and recessional velocity with galaxies of known
redshift. We review the observing technique, data reduction pipeline, and
catalog construction process, focusing on details of particular relevance to
understanding the catalog's compiled parameters. We further describe and make
available the digital HI line spectra associated with the catalogued sources.
In addition to the extragalactic HI line detections, we report nine confirmed
OH megamasers and ten OH megamaser candidates at 0.16 < z < 0.22 whose OH line
signals are redshifted into the ALFALFA frequency band. Because of complexities
in data collection and processing associated with the use of a feed-horn array
on a complex single-dish antenna in the terrestrial radio frequency
interference environment, we also present a list of suggestions and caveats for
consideration by users of the ALFALFA extragalactic catalog for future
scientific investigations.Comment: 24 pages 8 figures See http://egg.astro.cornell.edu/alfalfa/data for
ASCII and CSV datafiles corresponding to Table 2. To appear in
Astrophys.J.Supp
Galaxy pairs in the Sloan Digital Sky Survey – X. Does gas content alter star formation rate enhancement in galaxy interactions?
ALFALFA extragalactic HI source catalog
VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'The Arecibo Legacy Fast ALFA survey: The ALFALFA extragalactic HI source catalog.' (bibcode: 2018ApJ...861...49H