A population synthesis study of the luminosity function of hot white dwarfs

Context. We present a coherent and detailed Monte Carlo simulation of the population of hot white dwarfs. We assess the statistical significance of the hot end of the white dwarf luminosity function and the role played by the bolometric corrections of hydrogen-rich white dwarfs at high effective temperatures. Aims. We use the most up-to-date stellar evolutionary models and implement a full description of the observational selection biases to obtain realistic simulations of the observed white dwarf population. Methods. Our theoretical results are compared with the luminosity function of hot white dwarfs obtained from the Sloan Digital Sky Survey (SDSS), for both DA and non-DA white dwarfs. Results. We find that the theoretical results are in excellent agreement with the observational data for the population of white dwarfs with hydrogen deficient atmospheres (non-DA white dwarfs). For the population of white dwarfs with hydrogen-rich atmospheres (white dwarfs of the DA class), our simulations show some discrepancies with the observations for the brightest luminosity bins, namely those corresponding to luminosities larger than ~10 L.These discrepancies can be attributed to the way in which the masses of the white dwarfs contributing to this luminosity bin have been computed, as most of them have masses smaller than the theoretical lower limit for carbon-oxygen white dwarfs. Conclusions. We conclude that the way in which the observational luminosity function of hot white dwarfs is obtained is very sensitive to the particular implementation of the method used to derive the masses of the sample. We also provide a revised luminosity function for hot white dwarfs with hydrogen-rich atmospheres. © ESO, 2014.Peer ReviewedPostprint (published version

No Neutron Star Companion To The Lowest Mass SDSS White Dwarf

SDSS J091709.55+463821.8 (hereafter J0917+4638) is the lowest surface gravity white dwarf (WD) currently known, with log g = 5.55 +/- 0.05 (M ~ 0.17 M_sun; Kilic et al. 2007a,b). Such low-mass white dwarfs (LMWDs) are believed to originate in binaries that evolve into WD/WD or WD/neutron star (NS) systems. An optical search for J0917+4638's companion showed that it must be a compact object with a mass >= 0.28 M_sun (Kilic 2007b). Here we report on Green Bank Telescope 820 MHz and XMM-Newton X-ray observations of J0917+4638 intended to uncover a potential NS companion to the LMWD. No convincing pulsar signal is detected in our radio data. Our X-ray observation also failed to detect X-ray emission from J0917+4638's companion, while we would have detected any of the millisecond radio pulsars in 47 Tuc. We conclude that the companion is almost certainly another WD.Comment: 4 pages, 1 table; to appear in the Astrophysical Journal Letter

A Strategy for Finding Near Earth Objects with the SDSS Telescope

We present a detailed observational strategy for finding Near Earth Objects (NEOs) with the Sloan Digital Sky Survey (SDSS) telescope. We investigate strategies in normal, unbinned mode as well as binning the CCDs 2x2 or 3x3, which affects the sky coverage rate and the limiting apparent magnitude. We present results from 1 month, 3 year and 10 year simulations of such surveys. For each cadence and binning mode, we evaluate the possibility of achieving the Spaceguard goal of detecting 90% of 1 km NEOs (absolute magnitude H <= 18 for an albedo of 0.1). We find that an unbinned survey is most effective at detecting H <= 20 NEOs in our sample. However, a 3x3 binned survey reaches the Spaceguard Goal after only seven years of operation. As the proposed large survey telescopes (PanStarss; LSST) are at least 5-10 years from operation, an SDSS NEO survey could make a significant contribution to the detection and photometric characterization of the NEO population.Comment: Accepted by AJ -- 12 pages, 11 figure

Sloan Digital Sky Survey Multicolor Observations of GRB010222

The discovery of an optical counterpart to GRB010222 (detected by BeppoSAX; Piro 2001) was announced 4.4 hrs after the burst by Henden (2001a). The Sloan Digital Sky Survey's 0.5m photometric telescope (PT) and 2.5m survey telescope were used to observe the afterglow of GRB010222 starting 4.8 hours after the GRB. The 0.5m PT observed the afterglow in five, 300 sec g' band exposures over the course of half an hour, measuring a temporal decay rate in this short period of F_nu \propto t^{-1.0+/-0.5}. The 2.5m camera imaged the counterpart nearly simultaneously in five filters (u' g' r' i' z'), with r' = 18.74+/-0.02 at 12:10 UT. These multicolor observations, corrected for reddening and the afterglow's temporal decay, are well fit by the power-law F_nu \propto nu^{-0.90+/-0.03} with the exception of the u' band UV flux which is 20% below this slope. We examine possible interpretations of this spectral shape, including source extinction in a star forming region.Comment: 8 pages, 4 figures, accepted for publication in ApJ. Two figures added, minor changes to text in this draft. Related material can be found at: http://sdss.fnal.gov:8000/grb

“A Massive Long Way”: Interconnecting Histories, a “Special Child,” ADHD, and Everyday Family Life

Focusing on one family from a study of dual-earner middle-class families carried out in Los Angeles, California, this article draws on interview and video-recorded data of everyday interactions to explore illness and healing as embedded in the microcultural context of the Morris family. For this family, an important aspect of what is at stake for them in their daily lives is best understood by focusing on 9-year-old Mark, who has been diagnosed with attention-deficit/hyperactivity disorder (ADHD). In this article, we grapple with the complexity of conveying some sense of how Mark’s condition is experienced and relationally enacted in everyday contexts. Through illuminating connections between lives as lived and lives as told, we explore the narrative structuring of healing in relation to Mark’s local moral world with the family at its center. We examine how his parents understand the moral consequences of the child’s past for his present and future, and work to encourage others to give due weight to his troubled beginnings before this child joined the Morris family. At the same time, we see how the Morris parents act to structure Mark’s moral experience and orient to a desired future in which Mark’s “success” includes an appreciation of how he is accountable to others for his actions. Through our analyses, we also seek to contribute to discussions on what is at stake in everyday life contexts for children with ADHD and their families, through illuminating aspects of the cultural, moral and relational terrain that U.S. families navigate in contending with a child’s diagnosis of ADHD. Further, given that ADHD is often construed as a “disorder of volition,” we seek to advance anthropological theorizing about the will in situations where volitional control over behavior is seen to be disordered

The Environment of Passive Spiral Galaxies in the SDSS

In previous work on galaxy clusters, several authors reported a discovery of an unusual population of galaxies, which have spiral morphologies, but do not show any star formation activity. These galaxies are called ``passive spirals'', and have been interesting since it has been difficult to understand the existence of such galaxies. Using a volume limited sample (0.05<z<0.1 and Mr<-20.5; 25813 galaxies) of the Sloan Digital Sky Survey data, we have found 73 (0.28$\pm$0.03%) passive spiral galaxies and studied their environments. It is found that passive spiral galaxies live in local galaxy density 1-2 Mpc$^{-2}$ and 1-10 cluster-centric virial radius. Thus the origins of passive spiral galaxies are likely to be cluster related. These characteristic environments coincide with the previously reported environment where galaxy star formation rate suddenly declines and the so-called morphology-density relation turns. It is likely that the same physical mechanism is responsible for all of these observational results. The existence of passive spiral galaxies suggests that a physical mechanism that works calmly is preferred to dynamical origins such as major merger/interaction since such a mechanism can destroy spiral arm structures. Compared with observed cluster galaxy evolution such as the Butcher-Oemler effect and the morphological Butcher-Oemler effect, passive spiral galaxies are likely to be a galaxy population in transition between red, elliptical/S0 galaxies in low redshift clusters and blue, spiral galaxies more numerous in higher redshift clusters.Comment: 31 pages, 13 figures, PASJ in pres

SDSSJ103913.70+533029.7: A Super Star Cluster in the Outskirts of a Galaxy Merger

We describe the serendipitous discovery in the spectroscopic data of the Sloan Digital Sky Survey of a star-like object, SDSSJ103913.70+533029.7, at a heliocentric radial velocity of +1012 km/s. Its proximity in position and velocity to the spiral galaxy NGC 3310 suggests an association with the galaxy. At this distance, SDSSJ103913.70+533029.7 has the luminosity of a super star cluster and a projected distance of 17 kpc from NGC 3310. Its spectroscopic and photometric properties imply a mass of > 10^6 solar masses and an age close to that of the tidal shells seen around NGC 3310, suggesting that it formed in the event which formed the shells.Comment: Accepted by AJ: 4 figures (1 color