arXiv subjects

D. Burstein

Publications and source records attributed to D. Burstein.

16 recordsLinked to original sources

arXiv2008

A HST/WFPC2 survey of bright young clusters in M31. I. VdB0, a massive star cluster seen at ~= 25 Myr

{Aims.} We introduce our imaging survey of possible young massive globular clusters in M31 performed with the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST). We present here details of the data reduction pipeline that is being applied to all the survey data and describe its application to the brightest among our targets, van den Bergh 0 (VdB0), taken as a test case. {Methods.} The reddening, the age and the metallicity of the cluster are estimated by comparison of the observed Color Magnitude Diagram (CMD) with theoretical isochrones. {Results.} Under the most conservative assumptions the stellar mass of VdB0 is M > 2.4 x 10^4 M_sun, but our best estimates lie in the range ~ 4-9 x 10^4 M_sun. The CMD of VdB0 is best reproduced by models having solar metallicity and age = 25 Myr. Ages smaller than = 12 Myr and larger than = 60 Myr are clearly ruled out by the available data. The cluster has a remarkable number of Red Super Giants (> 18) and a CMD very similar to Large Magellanic Cloud clusters usually classified as young globulars such as NGC 1850, for example. {Conclusions.} VdB0 is significantly brighter (>~ 1 mag) than Galactic open clusters of similar age. Its present-day mass and half-light radius (r_h=7.4 pc) are more typical of faint globular clusters than of open clusters. However, given its position within the disk of M31 it is expected to be destroyed by dynamical effects, in particular by encounters with giant molecular clouds, within the next ~ 4 Gyr.

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arXiv2005

Hot Populations in M87 Globular Clusters

We have obtained HST/STIS far- and near-UV photometry of globular clusters in four fields in the gE galaxy M87. To a limit of m(FUV) = 25 we detect a total of 66 globular clusters (GCs) in common with the deep HST optical-band study of Kundu et al. (1999). Despite strong overlap in V- and I-band properties, the M87 GCs have UV/optical properties that are distinct from clusters in the Milky Way and in M31. M87 clusters, especially metal-poor ones, produce larger hot HB populations than do Milky Way analogues. Cluster mass is probably not a factor in these distinctions. The most metal-rich M87 GCs in our sample are near Z_sun and overlap the local E galaxy sample in estimated Mg_2 line indices. Nonetheless, the clusters produce much more UV light at a given Mg_2, being up to 1 mag bluer than any gE galaxy in (FUV-V) color. The M87 GCs do not appear to represent a transition between Milky Way-type clusters and E galaxies. The differences are in the correct sense if the clusters are significantly older than the E galaxies. Comparisons with Galactic open clusters indicate that the hot stars lie on the extreme horizontal branch, rather than being blue stragglers, and that the EHB becomes well populated for ages > 5 Gyr. We find that 43 of our UV detections have no optical-band counterparts. Most appear to be UV-bright background galaxies, seen through M87. Eleven NUV variable sources detected at only one epoch in the central field are probably classical novae. [Abridged]

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arXiv2005

UV/Optical Nuclear Activity in the gE Galaxy NGC 1399

Using HST/STIS, we have detected far-ultraviolet nuclear activity in the giant elliptical galaxy NGC 1399, the central and brightest galaxy in the Fornax I cluster. The source reached a maximum observed far-UV luminosity of \~1.2 x 10e39 ergs/s in January 1999. It was detectable in earlier HST archival images in 1996 (B band) but not in 1991 (V band) or 1993 (UV). It faded by a factor of ~4x by mid-2000. The source is almost certainly associated with the low luminosity AGN responsible for the radio emission in NGC 1399. The properties of the outburst are remarkably similar to the UV-bright nuclear transient discovered earlier in NGC 4552 by Renzini et al. (1995). The source is much fainter than expected from its Bondi accretion rate (estimated from Chandra high resolution X-ray images), even in the context of "radiatively inefficient accretion flow" models, and its variability also appears inconsistent with such models. High spatial resolution UV monitoring is a valuable means to study activity in nearby LLAGNs.

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arXiv2004

Peculiar velocities in the Zone of Avoidance: Determining the Distance to the Norma cluster

Deep J, H and Ks photometry of the low Galactic latitude Norma cluster has been obtained with the 1.4-m Infrared Survey Facility (IRSF) and with SOFI on the NTT. Together with spectroscopy taken at the Anglo-Australian Observatory using 2dF, the near-infrared Fundamental Plane of the Norma cluster will be used to determine the distance to this cluster and to assess its location within the Great Attractor overdensity. Potential systematic uncertainties related to the determination of peculiar velocities in the Zone of Avoidance are discussed in some detail. In particular the effects (uncertainties, systematics and scatter) of extinction and star-crowding on the derived magnitudes at low latitudes are investigated in great detail. We present a first look at the emerging Ks-band Fundamental Plane of the Norma cluster. We expect an uncertainty of ~ 3% (~ 150 km/s at the distance of the Norma cluster) in our final Fundamental Plane distance estimate based on 76 galaxies.

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arXiv2004

Globular Cluster and Galaxy Formation: M31, the Milky Way and Implications for Globular Cluster Systems of Spiral Galaxies

The globular cluster (GC) systems of the Milky Way and of our neighboring spiral galaxy, M31, comprise 2 distinct entities, differing in 3 respects. 1. M31 has young GCs, ages from ~100 Myr to 5 Gyr old, as well as old globular clusters. No such young GCs are known in the Milky Way. 2. We confirm that the oldest M31 GCs have much higher nitrogen abundances than do Galactic GCs at equivalent metallicities. 3. Morrison et al. found M31 has a subcomponent of GCs that follow closely the disk rotation curve of M31. Such a GC system in our own Galaxy has yet to be found. These data are interpreted in terms of the hierarchical-clustering-merging (HCM) paradigm for galaxy formation. We infer that M31 has absorbed more of its dwarf systems than has the Milky Way. This inference has 3 implications: 1. All spiral galaxies likely differ in their GC properties, depending on how many companions each galaxy has, and when the parent galaxy absorbs them. The the Milky Way ties down one end of this spectrum, as almost all of its GCs were absorbed 10-12 Gyr ago. 2. It suggests that young GCs are preferentially formed in the dwarf companions of parent galaxies, and then absorbed by the parent galaxy during mergers. 3. Young GCs seen in tidally-interacting galaxies might come from dwarf companions of these galaxies, rather than be made a-new in the tidal interaction. There is no ready explanation for the marked difference in nitrogen abundance for old M31 GCs relative to the oldest Galactic GCs. The predictions made by Li & Burstein regarding the origin of nitrogen abundance in globular clusters are consistent with what is found for the old M31 GCs compared to that for the two 5 Gyr-old M31 GCs.

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arXiv2004

Is the Giant Elliptical Galaxy NGC5018 a Post-Merger Remnant?

NGC5018, one of the weakest UV emitters among giant ellipticals (gE) observed with IUE, appears to consist of an optical stellar population very similar to that of the compact, dwarf elliptical M32, which is several magnitudes fainter in luminosity than NGC5018 and whose stellar population is know to be ~3 Gyr old. Here we show that the mid-UV spectra of these two galaxies are also very similar down to an angular scale hundreds times smaller than the IUE large aperture (as probed by HST/FOS UV spectra obtained through 0.86 arcsec apertures). This implies a reasonably close match of the populations dominating their mid-UV light (namely, their main-sequence turnoff stars). These data indicate that NGC5018 has, in its inner regions, a rather uniform dominance of a ~3 Gyr-old stellar population, probably a bit different in metallicity from M32. Combined with the various structures that indicate that NGC5018 is the result of a recent major merger, it appears that almost all of stars we see in its center regions were formed about 3 Gyr ago, in that merger event. NGC5018 is likely the older brother of NGC7252, the canonical gE-in-formation merger. As such, NGC5018 is perhaps the best galaxy which can tell us how a merger works, after the fireworks subside, to form a gE galaxy today. For this reason alone, the stellar populations in NGC5018 at all radii are worth studying in detail.

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arXiv2003

H-alpha +[NII] Observations of the HII Regions in M81

In a first of a series of studies of the H-alpha + [NII] emission from nearby spiral galaxies, we present measurements of H-alpha + [NII] emission from HII regions in M81. Our method uses large-field-CCD images and long-slit spectra, and is part of the ongoing Beijing-Arizona-Taipei-Connecticut Sky Survey. The CCD images are taken with the NAOC 0.6/0.9m f/3 Schmidt telescope at the Xinglong Observing Station, using a multicolor filter set. Spectra of 10 of the brightest HII regions are obtained using the NAOC 2.16m telescope with a Tek 1024 X 1024 CCD. The continua of the spectra are calibrated by flux-calibrated images taken from the Schmidt observations. We determine the continuum component of our H-alpha + [NII] image via interpolation from the more accurately-measured backgrounds (M81 starlight) obtained from the two neighboring (in wavelength) BATC filter images. We use the calibrated fluxes of H-alpha + [NII] emission from the spectra to normalize this interpolated, continuum-subtracted H-alpha + [NII] image. We estimate the zero point uncertainty of the measured H-alpha + [NII] emission flux to be $\sim$ 8%. A catalogue of H-alpha + [NII] fluxes for 456 HII regions is provided, with those fluxes are on a more consistent linear scale than previously available. The logarithmically-binned H-alpha + [NII] luminosity function of HII regions is found to have slope $α$ = -0.70, consistent with previous results (which allowed $α=-0.5 \sim -0.8$). From the overall H-alpha + [NII] luminosity of the HII regions, the star formation rate of M81 is found to be $\sim 0.68 M_{\odot} {\rm yr}^{-1}$, modulo uncertainty with extinction corrections.

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arXiv2001

The Distance to SN 1999em from the Expanding Photosphere Method

We present optical and IR spectroscopy of the first two months of evolution of the Type II SN 1999em. We combine these data with high-quality optical/IR photometry beginning only three days after shock breakout, in order to study the performance of the ``Expanding Photosphere Method'' (EPM) in the determination of distances. With this purpose we develop a technique to measure accurate photospheric velocities by cross-correlating observed and model spectra. The application of this technique to SN 1999em shows that we can reach an average uncertainty of 11% in velocity from an individual spectrum. Our analysis shows that EPM is quite robust to the effects of dust. In particular, the distances derived from the VI filters change by only 7% when the adopted visual extinction in the host galaxy is varied by 0.45 mag. The superb time sampling of the BVIZJHK light-curves of SN 1999em permits us to study the internal consistency of EPM and test the dilution factors computed from atmosphere models for Type II plateau supernovae. We find that, in the first week since explosion, the EPM distances are up to 50% lower than the average, possibly due the presence of circumstellar material. Over the following 65 days, on the other hand, our tests lend strong credence to the atmosphere models, and confirm previous claims that EPM can produce consistent distances without having to craft specific models to each supernova. This is particularly true for the VI filters which yield distances with an internal consistency of 4%. From the whole set of BVIZJHK photometry, we obtain an average distance of 7.5+/-0.5 Mpc, where the quoted uncertainty (7%) is a conservative estimate of the internal precision of the method obtained from the analysis of the first 70 days of the supernova evolution.

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arXiv2000

The peculiar motions of early-type galaxies in two distant regions - VII. Peculiar velocities and bulk motions

We present peculiar velocities for 84 clusters of galaxies in two large volumes at distances between 6000 and 15000 km/s in the directions of Hercules-Corona Borealis and Perseus-Pisces-Cetus. These velocities are based on Fundamental Plane (FP) distance estimates for early-type galaxies in each cluster. We fit the FP using a maximum likelihood algorithm which accounts for both selection effects and measurement errors, and yields FP parameters with smaller bias and variance than other fitting procedures. We find a best-fit FP with coefficients consistent with the best existing determinations. We measure the bulk motions of the sample volumes using the 50 clusters with the best-determined peculiar velocities. We find the bulk motions in both regions are small, and consistent with zero at about the 5% level. The EFAR results are in agreement with the small bulk motions found by Dale et al. (1999) on similar scales, but are inconsistent with pure dipole motions having the large amplitudes found by Lauer & Postman (1994) and Hudson et al. (1999). The alignment of the EFAR sample with the Lauer & Postman dipole produces a strong rejection of a large-amplitude bulk motion in that direction, but the rejection of the Hudson et al. result is less certain because their dipole lies at a large angle to the main axis of the EFAR sample. We find the bulk motion of our sample is consistent with most cosmological models that approximately reproduce the shape and normalisation of the observed galaxy power spectrum. We conclude that existing measurements of large-scale bulk motions provide no significant evidence against standard models for the formation of structure.

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arXiv2000

Astronomers and the Science Citation Index, 1981--1997

The Institute for Science Information (ISI) has generated two lists of citation information for astronomers that are uniquely restricted both as to the years surveyed for the cited papers, and the years surveyed for the citing papers. The main list gives citation data for 62,813 physicists and astronomers whose journal papers were cited 100 times or more from 1981.0 to 1997.5 by papers published during the same time interval. The second list gives the 200 most-cited papers/year published in refereed astronomical journals from 1981-1996, as cited in papers in those same journals from 1981.0-1998.0. Astronomer names were selected from various sources. From this work an Astronomy Citation Database (ACD) has been constructed, containing citation data for 6458+ astronomers, plus additional data for 173 astronomers and the top-10 cited papers published 1981-1996. Various problems, both substantial and subtle, of producing a reasonably fair citation database are detailed. Chief among these are whether to assign either parital or full credit for each author on a given paper. Whether one is honored with one of the top astronomy lifetime-awards is a strong function of how well your work stands out as your own, and in what kind of publications you publish (e.g., the ISI does not keep track of papers in meeting proceedings/books/catalogs). Name confusion affects this kind of analysis to the extent that that it would take an enormous effort to disentangle its effects and, even then, not all name confusion would be settled. A ``modest proposal'' is made that our professional field (and others) go to a system of uniquely associating an identification number to each author on each paper to solve the name confusion problem.

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arXiv1999

Deep Intermediate-Band Surface Photometry of NGC 5907

We obtained very deep exposures of NGC 5907 with a Schmidt telescope, large-format CCD, and intermediate-band filters centered at 6660A and 8020A. These two filters, part of a 15-filter set, are custom-designed to avoid the brightest (and most variable) night sky lines, with the result that our images go deeper, with lower sky noise, than those taken with broad-band filters. Our errors of observation reach 1 mag/arcsec^2 at 29.00 mag/arcsec-2 in the 6660A image (= 28.7 in R-band), and 27.4 mag/arcsec^ in the 8020A image (same zero point as I-band). Fainter than R = 27 mag arcsec^, the surface brightness around NGC 5907 is strongly asymmetric, being mostly brighter the NW side of the galaxy midplane. This asymmetry rules out a halo for the origin of the faint surface brightness we see. Rather, this asymmetry is likely an artifact due to a combination of light from a faint ring around this galaxy (as described in Shang et al. 1998, ApJL 504, 23) and residual surface brightness at faint levels from stars that our star-masking procedure cannot completely eliminate. Good agreement with the surface photometry of NGC 5907 by Morrison et al. and other workers lead us to conclude that their data are similarly affected at faint levels by ring light and residual effects from their star masking procedures. Inspection of the images published by Morrison et al. and Sackett et al. confirm this to be the case. Thus, we conclude that NGC 5907 does not have a faint, extended halo.

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arXiv1998

POTENT Reconstruction from Mark III Velocities

We present an improved POTENT method for reconstructing the velocity and mass density fields from radial peculiar velocities, test it with mock catalogs, and apply it to the Mark III Catalog. Method improvments: (a) inhomogeneous Malmquist bias is reduced by grouping and corrected in forward or inverse analyses of inferred distances, (b) the smoothing into a radial velocity field is optimized to reduce window and sampling biases, (c) the density is derived from the velocity using an improved nonlinear approximation, and (d) the computational errors are made negligible. The method is tested and optimized using mock catalogs based on an N-body simulation that mimics our cosmological neighborhood, and the remaining errors are evaluated quantitatively. The Mark III catalog, with ~3300 grouped galaxies, allows a reliable reconstruction with fixed Gaussian smoothing of 10-12 Mpc/h out to ~60 Mpc/h. We present maps of the 3D velocity and mass-density fields and the corresponding errors. The typical systematic and random errors in the density fluctuations inside 40 Mpc/h are \pm 0.13 and \pm 0.18. The recovered mass distribution resembles in its gross features the galaxy distribution in redshift surveys and the mass distribution in a similar POTENT analysis of a complementary velocity catalog (SFI), including the Great Attractor, Perseus-Pisces, and the void in between. The reconstruction inside ~40 Mpc/h is not affected much by a revised calibration of the distance indicators (VM2, tailored to match the velocities from the IRAS 1.2Jy redshift survey). The bulk velocity within the sphere of radius 50 Mpc/h about the Local Group is V_50=370 \pm 110 km/s (including systematic errors), and is shown to be mostly generated by external mass fluctuations. With the VM2 calibration, V_50 is reduced to 305 \pm 110 km/s.

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arXiv1998

UV Spectra, Line Indices of M31 Globular Clusters and E Galaxy Cores

Observations in integrated light (2200-4800 A, 8 to 11 A resolution, S/N > 20) of 4 M31 globular clusters and of the cores of six gE galaxies made with the HST/FOS are presented and analyzed. These data are supplemented by IUE observations of M32, Galactic globulars and stars. From these data we measure UV colors and absorption line strength (ALS) indices, including the key NH feature at 3360 A. We find that our data divide the M31 globular clusters, Galactic globular clusters/Galactic stars, and gE galaxies into three different stellar populations. The old stellar populations of M31 globular clusters and elliptical galaxies are more similar to each other than each is to the Galactic stellar population. Of special note is that the NH feature is so strong in the spectra of M31 globulars that a large (>20) overabundance in nitrogen in these stars, relative to that in Galactic stars, is likely required. Other ALS indices (of Mg, Al) also show significant differences.

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arXiv1997

The Axis Ratio Distribution of Local and Distant Galaxies

Surface photometry from 16 HST/WFPC2 fields in the I(F814W) filter is used to derive the distribution of apparent axis ratios for galaxies in progressively fainter magnitude intervals for I<25. We assess the systematic and accidental errors in ellipticity measurements as a function of image resolution and signal-to-noise ratio, and statistically correct for the effect of cosmological surface brightness dimming on our isophotal measurements. The axis ratio distribution for the local galaxy population was computed using logR measurements for 1569 RC3 galaxies with Bt<13 mag. Nonparametric tests are used to show that our distant samples, in the redshift range 0.1<z<1.5, are not statistically different from the local sample. We present image montages of galaxies selected randomly from different axis ratio and apparent magnitude ranges and discuss the evolutionary consequences of the lack of a strong difference between the ellipticity distributions in near and far data sets.

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arXiv1996

The Peculiar Motions of Early-Type Galaxies in Two Distant Regions. IV. The Photometric Fitting Procedure

The EFAR project is a study of 736 candidate early-type galaxies in 84 clusters lying in two regions towards Hercules-Corona Borealis and Perseus-Cetus at distances $cz \approx 6000-15000$ km/s. In this paper we describe a new method of galaxy photometry adopted to derive the photometric parameters of the EFAR galaxies. The algorithm fits the circularized surface brightness profiles as the sum of two seeing-convolved components, an $R^{1/4}$ and an exponential law. This approach allows us to fit the large variety of luminosity profiles displayed by the EFAR galaxies homogeneously and to derive (for at least a subset of these) bulge and disk parameters. Multiple exposures of the same objects are optimally combined and an optional sky-fitting procedure has been developed to correct for sky subtraction errors. Extensive Monte Carlo simulations are analyzed to test the performance of the algorithm and estimate the size of random and {\it systematic} errors. Random errors are small, provided that the global signal-to-noise ratio of the fitted profiles is larger than $\approx 300$. Systematic errors can result from 1) errors in the sky subtraction, 2) the limited radial extent of the fitted profiles, 3) the lack of resolution due to seeing convolution and pixel sampling, 4) the use of circularized profiles for very flattened objects seen edge-on and 5) a poor match of the fitting functions to the object profiles. Large systematic errors are generated by the widely used simple $R^{1/4}$ law to fit luminosity profiles when a disk component, as small as 20% of the total light, is present.

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arXiv1994

Recalibration of the H$_{\bf -0.5}$ Magnitudes of Spiral Galaxies

The H magnitude aperture data published by the Aaronson et al. collaboration over a 10-year period is collected into a homogeneous data set of 1731 observations of 665 galaxies. 96\% of these galaxies have isophotal diameters and axial ratios determined by the Third Reference Catalogue of Bright Galaxies (de Vaucouleurs et al. 1991), the most self-consistent set of optical data currently available. The precepts governing the optical data in the RC3 are systematically different from those of the Second Reference Catalogue (de Vaucouleurs, de Vaucouleurs and Corwin 1976), which were used by Aaronson et al. for their original analyses of galaxy peculiar motions. This in turn leads to systematic differences in growth curves and fiducial H magnitudes, prompting the present recalibration of the near-infrared Tully Fisher relationship. New optically-normalized H magnitude growth curves are defined for galaxies of types S0 to Im, from which new values of fiducial H magnitudes, H$\rm _{-0.5}^g$, are measured for the 665 galaxies. A series of internal tests show that these four standard growth curves are defined to an accuracy of 0.05 mag over the interval $\rm -1.5 \leq \log (A/D_g) \leq -0.2$. Comparisons with the Aaronson et al. values of diameters, axial ratios and fiducial H magnitudes show the expected differences, given the different definitions of these parameters. The values of H$\rm _{-0.5}^g$ are assigned quality indices; a value of 1 indicates an accuracy of $<$0.2 magnitude; Quality 2 indicates an accuracy of 0.2 to 0.35 mag; and Quality 3 indicates $>$0.35 mag. Revised values of corrected HI velocity widths are also given, based on the new set of axial ratios defined by the RC3.

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