Traces of Thermalization from Transverse Momentum Fluctuations in Nuclear Collisions

Scattering of particles produced in Au+Au collisions at RHIC can wrestle the system into a state near local thermal equilibrium. I illustrate how measurements of the centrality dependence of the mean transverse momentum and its fluctuations can exhibit this thermalization.Comment: 4 pages, 2 eps figures, final version to appear in PR

An IR Search for Extinguished Supernovae in Starburst Galaxies

IR and Radio band observations of heavily extinguished regions in starburst galaxies suggest a very high SN rate associated with such regions. Optically measured supernova (SN) rates may therefore underestimate the total SN rate by factors of up to 10, due to the high extinction to SNe in starburst regions. The IR/radio SN rates come from a variety of indirect means, however, which suffer from model dependence and other problems. We describe a direct measurement of the SN rate from a regular patrol of starburst galaxies done with K' band imaging to minimize the effects of extinction. A collection of K' measurements of core-collapse SNe near maximum light is presented. Results of a preliminary SN search using the MIRC camera at the Wyoming IR Observatory (WIRO), and an improved search using the ORCA optics are described. A monthly patrol of starburst galaxies within 25 Mpc should yield 1.6 - 9.6 SNe/year. Our MIRC search with low-resolution (2.2" pixels) failed to find extinguished SNe, limiting the SN rate outside the nucleus (at > 15" radius) to less than 3.8 Supernova Rate Units (SRU or SNe/century/10^10 L(solar); 90% confidence). The MIRC camera had insufficient resolution to search nuclear starburst regions, where SN activity is concentrated, explaining why we found no heavily obscured SNe. We conclude that high-resolution, small field SN searches in starburst nuclei are more productive than low resolution, large-field searches, even for our large galaxies. With our ORCA high-resolution optics, we could limit the total SN rate to < 1.3 SRU at 90% confidence in 3 years of observations, lower than the most pessimistic estimate.Comment: AJ Submitted 1998 Dec. 13. View figures and download all as one file at http://panisse.lbl.gov/public/bruce/irs

Discovery of two infrared supernovae: a new window on the SN search

We report the discovery of two supernovae (SN 1999gw and SN 2001db) obtained within the framework of an infrared monitoring campaign of Luminous Infrared Galaxies, aimed at detecting obscured supernovae. SN 2001db, extinguished by Av~5.5 mag, is the first supernova discovered in the infrared which has received the spectroscopic confirmation. This result highlights the power of infrared monitoring in detecting obscured SNe and indicates that optical surveys are probably missing a significant fraction of SNe, especially in obscured systems such as starburst galaxies. The preliminary estimate of SN rate in LIRG galaxies is about an order of magnitude higher than that expected from optical surveys.Comment: 9 pages, 7 figures, accepted for publication in A&

Optical Observations of the Binary Pulsar System PSR B1718-19: Implications for Tidal Circularization

We report on Keck and Hubble Space Telescope optical observations of the eclipsing binary pulsar system PSR B1718-19, in the direction of the globular cluster NGC 6342. These reveal a faint star ($m_{\rm F702W}=25.21\pm0.07$; Vega system) within the pulsar's 0\farcs5 radius positional error circle. This may be the companion. If it is a main-sequence star in the cluster, it has radius \rcomp\simeq0.3 \rsun, temperature \teff\simeq3600 K, and mass \mcomp\simeq0.3 \msun. In many formation models, however, the pulsar (spun up by accretion or newly formed) and its companion are initially in an eccentric orbit. If so, for tidal circularization to have produced the present-day highly circular orbit, a large stellar radius is required, i.e., the star must be bloated. Using constraints on the radius and temperature from the Roche and Hayashi limits, we infer from our observations that \rcomp\simlt0.44 \rsun and \teff\simgt3300 K. Even for the largest radii, the required efficiency of tidal dissipation is larger than expected for some prescriptions.Comment: 10 pages, 2 figures, aas4pp2.sty. Accepted for publication in Ap

Sequential drain amylase to guide drain removal following pancreatectomy

BACKGROUND: Although used as criterion for early drain removal, postoperative day (POD) 1 drain fluid amylase (DFA) ≤ 5000 U/L has low negative predictive value for clinically relevant postoperative pancreatic fistula (CR-POPF). It was hypothesized that POD3 DFA ≤ 350 could provide further information to guide early drain removal. METHODS: Data from a pancreas surgery consortium database for pancreatoduodenectomy and distal pancreatectomy patients were analyzed retrospectively. Those patients without drains or POD 1 and 3 DFA data were excluded. Patients with POD1 DFA ≤ 5000 were divided into groups based on POD3 DFA: Group A (≤350) and Group B (>350). Operative characteristics and 60-day outcomes were compared using chi-square test. RESULTS: Among 687 patients in the database, all data were available for 380. Fifty-five (14.5%) had a POD1 DFA > 5000. Among 325 with POD1 DFA ≤ 5000, 254 (78.2%) were in Group A and 71 (21.8%) in Group B. Complications (35 (49.3%) vs 87 (34.4%); p = 0.021) and CR-POPF (13 (18.3%) vs 10 (3.9%); p < 0.001) were more frequent in Group B. CONCLUSIONS: In patients with POD1 DFA ≤ 5000, POD3 DFA ≤ 350 may be a practical test to guide safe early drain removal. Further prospective testing may be useful

The infrared supernova rate in starburst galaxies

We report the results of our ongoing search for extincted supernovae (SNe) at near-infrared wavelengths. We have monitored at 2.2 micron a sample of 46 Luminous Infrared Galaxies and detected 4 SNe. The number of detections is still small but sufficient to provide the first estimate of supernova rate at near-infrared wavelengths. We measure a SN rate ofv 7.6+/-3.8 SNu which is an order of magnitude larger than observed in quiescent galaxies. On the other hand, the observed near-infrared rate is still a factor 3-10 smaller than that estimated from the far-infrared luminosity of the galaxies. Among various possibilities, the most likely scenario is that dust extinction is so high (Av>30) to obscure most SNe even in the near-IR. The role of type Ia SNe is also discussed within this context. We derive the type Ia SN rate as a function of the stellar mass of the galaxy and find a sharp increase toward galaxies with higher activity of star formation. This suggests that a significant fraction of type Ia SNe are associated with young stellar populations. Finally, as a by-product, we give the average K-band light curve of core-collapse SNe based on all the existing data, and review the relation between SN rate and far-infrared luminosity.Comment: A&A, in press, 13 page

Brown dwarfs in the Hyades and beyond?

We have used both the Low-Resolution Imaging Spectrograph and the HIRES echelle spectrograph on the Keck telescopes to obtain spectra of twelve candidate members of the Hyades cluster identified by Leggett and Hawkins (1988, 1989). All of the objects are chromospherically-active, late-type M-dwarfs, with H$\alpha$ equivalent widths varying from 1 to 30\AA. Based on our measured radial velocities, the level of stellar activity and other spectroscopic features, only one of the twelve stars has properties consistent with cluster membership. We consider how this result affects estimates of the luminosity and mass function of the Hyades cluster. Five of the eleven field stars have weak K I 7665/7699\AA and CaH absorption as compared with M-dwarf standards of the same spectral type, suggesting a lower surface gravity. Two of these sources, LH0416+14 and LH0419+15, exhibit significant lithium 6708 \AA absorption. Based partly on parallax measurements by the US Naval Observatory (Harris et al, 1998), we identify all five as likely to be young, pre-main sequence objects in or near the Taurus-Auriga association at distances of between 150 and 250 parsecs. A comparison with theoretical models of pre-main sequence stars indicates masses of less than 0.05 M$_\odot$.Comment: to appear in AJ, January 1999; 34 pages, (Latex format), including 10 embedded postscript figures and two table

An Interstellar Conduction Front Within a Wolf-Rayet Ring Nebula Observed with the GHRS

With the High Resolution Spectrograph aboard the Hubble Space Telescope we obtained high signal-to-noise (S/N > 200 - 600 per 17 km/s resolution element) spectra of narrow absorption lines toward the Wolf-Rayet star HD 50896. The ring nebula S308 that surrounds this star is thought to be caused by a pressure-driven bubble bounded by circumstellar gas (most likely from a red supergiant or luminous blue variable progenitor) pushed aside by a strong stellar wind. Our observation has shown for the first time that blueshifted (approximately 70 km/s relative to the star) absorption components of C IV and N V arise in a conduction front between the hot interior of the bubble and the cold shell of swept-up material. These lines set limits on models of the conduction front. Nitrogen in the shell appears to be overabundant by a factor ~10. The P Cygni profiles of N V and C IV are variable, possibly due to a suspected binary companion to HD 50896.Comment: 32 pages, Latex, to appear in the Astrophysical Journal, April, 199