arXiv subjects

Robert Blum

Publications and source records attributed to Robert Blum.

28 records · Page 2Linked to original sources

arXiv2013

Three New Galactic Center X-ray Sources Identified with Near-Infrared Spectroscopy

We have conducted a near-infrared spectroscopic survey of 47 candidate counterparts to X-ray sources discovered by the Chandra X-ray Observatory near the Galactic Center (GC). Though a significant number of these astrometric matches are likely to be spurious, we sought out spectral characteristics of active stars and interacting binaries, such as hot, massive spectral types or emission lines in order to corroborate the X-ray activity and certify the authenticity of the match. We present three new spectroscopic identifications, including a Be high mass X-ray binary (HMXB) or a gamma Cassiopeiae (Cas) system, a symbiotic X-ray binary and an O-type star of unknown luminosity class. The Be HMXB/gamma Cas system and the symbiotic X-ray binary are the first of their classes to be spectroscopically identified in the GC region.

astro-ph.GA↗

arXiv2013

The DESI Experiment, a whitepaper for Snowmass 2013

The Dark Energy Spectroscopic Instrument (DESI) is a massively multiplexed fiber-fed spectrograph that will make the next major advance in dark energy in the timeframe 2018-2022. On the Mayall telescope, DESI will obtain spectra and redshifts for at least 18 million emission-line galaxies, 4 million luminous red galaxies and 3 million quasi-stellar objects, in order to: probe the effects of dark energy on the expansion history using baryon acoustic oscillations (BAO), measure the gravitational growth history through redshift-space distortions, measure the sum of neutrino masses, and investigate the signatures of primordial inflation. The resulting 3-D galaxy maps at z<2 and Lyman-alpha forest at z>2 will make 1%-level measurements of the distance scale in 35 redshift bins, thus providing unprecedented constraints on cosmological models.

astro-ph.CO↗

arXiv2012

Addressing Decadal Survey Science through Community Access to Highly Multiplexed Spectroscopy with BigBOSS on the KPNO Mayall Telescope

This document summarizes the results of a community-based discussion of the potential science impact of the Mayall+BigBOSS highly multiplexed multi-object spectroscopic capability. The KPNO Mayall 4m telescope equipped with the DOE- and internationally-funded BigBOSS spectrograph offers one of the most cost-efficient ways of accomplishing many of the pressing scientific goals identified for this decade by the "New Worlds, New Horizons" report. The BigBOSS Key Project will place unprecedented constraints on cosmological parameters related to the expansion history of the universe. With the addition of an open (publicly funded) community access component, the scientific impact of BigBOSS can be extended to many important astrophysical questions related to the origin and evolution of galaxies, stars, and the IGM. Massive spectroscopy is the critical missing ingredient in numerous ongoing and planned ground- and space-based surveys, and BigBOSS is unique in its ability to provide this to the US community. BigBOSS data from community-led projects will play a vital role in the education and training of students and in maintaining US leadership in these fields of astrophysics. We urge the NSF-AST division to support community science with the BigBOSS multi-object spectrograph through the period of the BigBOSS survey in order to ensure public access to the extraordinary spectroscopic capability.

astro-ph.CO↗

arXiv2010

Near-infrared counterparts of Chandra X-ray sources toward the Galactic Center

The Chandra X-ray Observatory has now discovered nearly 10,000 X-ray point sources in the 2 x 0.8 degree region around the Galactic Center (Muno 2009). The sources are likely to be a population of accreting binaries in the Galactic Center, but little else is known of their nature. We obtained JHKs imaging of the 17'x 17' region around Sgr A*, an area containing 4339 of these X-ray sources, with the ISPI camera on the CTIO 4-m telescope. We cross-correlate the Chandra and ISPI catalogs to find potential IR counterparts to the X-ray sources. The extreme IR source crowding in the field means that it is not possible to establish the authenticity of the matches with astrometry and photometry alone. We find 2137 IR/X-ray astrometrically matched sources: statistically we estimate that our catalog contains 289 +/- 13 true matches to soft X-ray sources and 154 +/- 39 matches to hard X-ray sources. However, the fraction of true counterparts to candidate counterparts for hard sources is just 11 %, compared to 60 % for soft sources, making hard source NIR matches particularly challenging for spectroscopic follow-up. We calculate a color-magnitude diagram (CMD) for the matches to hard X-ray sources, and find regions where significant numbers of the IR matches are real. We use their CMD positions to place limits on the absolute Ks band magnitudes of the potential NIR counterparts to hard X-ray sources. We find regions of the counterpart CMD with 9 +/- 3 likely Wolf-Rayet/supergiant binaries (with 4 spectroscopically confirmed in the literature) as well as 44 +/- 13 candidates that could consist of either main sequence high mass X-ray binaries or red giants with an accreting compact companion. (abridged)

astro-ph.GA↗

arXiv2010

Nuclear Star Clusters and Black Holes

We summarize the recent results of our survey of the nearest nuclear star clusters. The purpose of the survey is to understand nuclear star cluster formation mechanisms and constrain the presence of black holes using adaptive optics assisted integral field spectroscopy, optical spectroscopy, and HST imaging in 13 galaxies within 5 Mpc. We discuss the formation history of the nuclear star cluster and possible detection of an intermediate mass BH in NGC 404, the nearest S0 galaxy.

astro-ph.CO↗

arXiv2006

Spitzer Survey of the Large Magellanic Cloud, Surveying the Agents of a Galaxy's Evolution (SAGE) I: Overview and Initial Results

We are performing a uniform and unbiased, ~7x7 degrees imaging survey of the Large Magellanic Cloud (LMC), using the IRAC and MIPS instruments on board the Spitzer Space Telescope in order to survey the agents of a galaxy's evolution (SAGE), the interstellar medium (ISM) and stars in the LMC. The detection of diffuse ISM with column densities >1.2x10^21 H cm^-2 permits detailed studies of dust processes in the ISM. SAGE's point source sensitivity enables a complete census of newly formed stars with masses >3 solar masses that will determine the current star formation rate in the LMC. SAGE's detection of evolved stars with mass loss rates >1x10^-8 solar masses per year will quantify the rate at which evolved stars inject mass into the ISM of the LMC. The observing strategy includes two epochs in 2005, separated by three months, that both mitigate instrumental artifacts and constrain source variability. The SAGE data are non-proprietary. The data processing includes IRAC and MIPS pipelines and a database for mining the point source catalogs, which will be released to the community in support of Spitzer proposal cycles 4 and 5. We present initial results on the epoch 1 data with a special focus on the N79 and N83 region. The SAGE epoch 1 point source catalog has ~4 million sources. The point source counts are highest for the IRAC 3.6 microns band and decrease dramatically towards longer wavelengths consistent with the fact that stars dominate the point source catalogs and that the dusty objects, e.g. young stellar objects and dusty evolved stars that detected at the longer wavelengths, are rare in comparison. We outline a strategy for identifying foreground MW stars, that may comprise as much as 18% of the source list, and background galaxies, that may comprise ~12% of the source list.

astro-ph↗

arXiv2002

NGC 3576 IRS 1 in the Mid Infrared

We present the results of high-resolution mid-infrared observations of the source NGC 3576 IRS 1. Near diffraction-limited images were taken at the Gemini South Observatory through OSCIR's filters N, 7.9, 9.8, 12.5 and IHW18. The source IRS 1 was resolved into 3 sources for the first time at mid-infrared wavelengths. For each source we constructed the SED from 1.25 to 18 microns, as well the color temperature and the spatial distribution of the dust in the region. The optical depth of the silicate absorption feature at 9.8 microns is presented also.

astro-ph↗

arXiv2000

Stellar Iron Abundances at the Galactic Center

We present measurements of [Fe/H] for six M supergiant stars and three giant stars within 0.5 pc of the Galactic Center (GC) and one M supergiant star within 30 pc of the GC. The results are based on high-resolution (lambda / Delta lambda =40,000) K-band spectra, taken with CSHELL at the NASA Infrared Telescope Facility.We determine the iron abundance by detailed abundance analysis,performed with the spectral synthesis program MOOG.The mean [Fe/H] of the GC stars is determined to be near solar,[Fe/H] = +0.12 $\pm$ 0.22. Our analysis is a differential analysis, as we have observed and applied the same analysis technique to eleven cool, luminous stars in the solar neighborhood with similar temperatures and luminosities as the GC stars. The mean [Fe/H] of the solar neighborhood comparison stars, [Fe/H] = +0.03 $\pm$ 0.16, is similar to that of the GC stars. The width of the GC [Fe/H] distribution is found to be narrower than the width of the [Fe/H] distribution of Baade's Window in the bulge but consistent with the width of the [Fe/H] distribution of giant and supergiant stars in the solar neighborhood.

astro-ph↗

arXiv1995

M Giant Kinematics in Off-Axis Fields Between 150 and 300 Parsecs from the Galactic Center

We present radial velocities for approximately 40 stars in each of three optically obscured, off-axis, fields toward the Galactic bulge. Combined with the data presented by Blum et al. (1994), we now have mean radial velocities and radial velocity dispersions in four fields towards the Galactic bulge. These four fields lie nearly along an axis whose position angle from the major axis of the Galaxy is 55°. The observed kinematics generally match both Kent's (1992) axisymmetric and Zhao's (1994) barred dynamical model predictions, but are marginally better described by the latter. The velocity dispersion in our innermost field is high, 153 $\pm$ 17 \kms. Our data, combined with that from previous studies at larger radii, suggest that the stellar velocity dispersion is flat or still rising at projected radius R \aple 150 pc.

astro-ph↗

arXiv1995

Figure Rotation and the Mass of the Galactic Bulge

The mass of the Galactic bulge, $M_B$, is estimated from the tensor virial theorem. By including the effects of a barred stellar distribution and figure rotation (81 \kms kpc $^{-1}$) and by assuming that the bar is oriented at $θ$ $=$ 20°\ to our line of sight, $M_B$ is found to be as high as 2.8$\times$10$^{10}$ M$_{\odot}$. This estimate is in good agreement with the total mass inferred from the observed optical depth to microlensing for stars toward the inner Galaxy. For larger angles, $θ$ $\sim$ 40°, or smaller pattern speeds (20 \kms kpc $^{-1}$), $M_B$ is found to be $\sim$ 1.7 $-$ 1.9$\times$10$^{10}$ M$_{\odot}$, similar to previous estimates for a barred bulge (2$\times$10$^{10}$ M$_{\odot}$) and axisymmetric bulge (1.8$\times$10$^{10}$ M$_{\odot}$).

astro-ph↗