9892560
Using STIS to find gamma-ray burst redshifts
A recent spectrum of the optical afterglow of GRB 970508 suggests that gamma-ray bursts (GRBs) are cosmological in origin, and it is of crucial importance to derive an accurate distance to each burst. If GRBs occur near their host galaxies (much less than 40 kpc) then Lyman limit absorption should be observable in roughly half the GRB afterglow spectra. Here we outline the methodology to obtain a redshift from the GRB afterglow spectrum using the recently installed Space Telescope Imaging Spectrograph (STIS) instrument on board HST. A low-resolution spectrum with the Multi-Anode Microchannel Array (MAMA) detector gives complete spectral coverage over the wavelength range 1570-3180 A and 1150-1740 A. Assuming that a Target of Opportunity observation is conducted soon (about 3 wk) after a bright burst, a relatively small integration time (about three orbits) would be sufficient to detect the Lyman limit over a wide redshift range (0.3-2.2). Detection (or nondetection) of the Lyman limit, in concert with ground-based observations of nearby galaxies and Mg II and C IV absorption lines, should provide meaningful constraints on the relationship of GRBs to galaxies.
18564854
Searching for the Precursors of Life in External Galaxies
Are the organic molecules crucial for life on Earth abundant in early-epoch galaxies? To address this, we searched for organic molecules in extragalactic sources via their absorption features, known as diffuse interstellar bands (DIBs). There is strong evidence that DIBs are associated with polycyclic aromatic hydrocarbons (PAHs) and carbon chains. Galaxies with a preponderance of DIBs may be the most likely places in which to expect life. 
We use the method of quasar absorption lines to probe intervening early-epoch galaxies for the DIBs. We present the equivalent width measurements of DIBs in one neutral hydrogen (HI) abundant galaxy and limits for five DIB bands in six other HI-rich galaxies (damped Lyman-alpha systems--DLAs). Our results reveal that HI-rich galaxies are dust poor and have significantly lower reddening than known DIB-rich Milky Way environments. We find that DIBs in HI-rich galaxies do not show the same correlation with hydrogen abundance as observed in the Milky Way; the extragalactic DIBs are underabundant by as much as 10 times. The lower limit gas-to-dust ratios of four of the HI-rich early epoch galaxies are much higher than the gas-to-dust ratios found in the Milky Way. Our results suggest that the organic molecules responsible for the DIBs are underabundant in HI-rich early epoch galaxies relative to the Milky Way.
16439685
Primordial or Dynamical Mass Segregation in Young LMC Clusters
We present the detailed analysis of Hubble Space Telescope observations of the spatial distributions of different stellar species in two young compact star clusters in the Large Magellanic Cloud, NGC 1805 and NGC 1818. Based on a comparison of the characteristic relaxation times in their cores and at their half-mass radii with the observed degree of mass segregation, it is most likely that significant primordial mass segregation was present in both clusters, particularly in NGC 1805. Both clusters were likely formed with very similar initial mass functions.
16316489
Constraints on Galaxy Formation from Stars in the Far Outer Disk of M31
Numerical simulations of galaxy formation within the cold dark matter (CDM) hierarchical clustering framework are unable to produce large disk galaxies without invoking some form of feedback to suppress gas cooling and collapse until a redshift of unity or below. An important observational consequence of delaying the epoch of disk formation until relatively recent times is that the stellar populations in the extended disk should be of predominantly young-to-intermediate age. We use a deep Hubble Space Telescope/Wide Field Planetary Camera 2 archival pointing to investigate the mean age and metallicity of the stellar population in a disk-dominated field at 30 kpc along the major axis of M31. Our analysis of the color-magnitude diagram reveals the dominant population to have a significant mean age (greater than or similar to8 Gyr) and a moderately high mean metallicity ([Fe/H] similar to -0.7); tentative evidence is also presented for a trace population of ancient (greater than or equal to 10 Gyr) metal-poor stars. These characteristics are unexpected in CDM models, and we discuss the possible implications of this result as well as alternative interpretations.
16449065
Stellar Abundances in Giant Stars in the Metal-Rich Globular Cluster NGC 6528
We present the first results of a detailed abundance analysis, based on VLT observations, of giant stars in the very metal-rich globular cluster NGC 6528. We will be able to tie the horizontal branch abundances (see e.g. Carretta et al. 2001) to those of the more luminous giants (see CMDs). For the very similar cluster NGC 6553 studies of different types of stars have yielded very disparate results. Our first analysis of three of our stars seem to indicate that indeed the different sorts of stars do show similar abundances if one homogeneous set of models and parameters are being used.
17629793
Limits on Reddening and Gas-to-Dust Ratios for Seven Intermediate Redshift Damped Lyα Absorbers from Diffuse Interstellar Bands
We present equivalent width measurements and limits of six diffuse interstellar bands (DIBs, λ4428, λ5705, λ5780, λ5797, λ6284, and λ6613) in seven damped Lyα absorbers (DLAs) over the redshift range 0.091 ≤ z ≤ 0.524, sampling 20.3 ≤ log N(H I) ≤ 21.7. DIBs were detected in only one of the seven DLAs, that which has the highest reddening and metallicity. Based upon the Galactic DIB-N(H I) relation, the λ6284 DIB equivalent width upper limits in four of the seven DLAs are a factor of 4-10 times below the λ6284 DIB equivalent widths observed in the Galaxy, but are not inconsistent with those present in the Magellanic Clouds. Assuming the Galactic DIB-E(B – V) relation, we determine reddening upper limits for the DLAs in our sample. Based upon the E(B – V) limits, the gas-to-dust ratios, N(H I)/E(B – V), of the four aforementioned DLAs are at least ~5 times higher than that of the Galactic interstellar medium. The ratios of two other DLAs are at least a factor of a few times higher. The best constraints on reddening derive from the upper limits for the λ5780 and λ6284 DIBs, which yield E(B – V) ≤ 0.08 for four of the seven DLAs. Our results suggest that, in DLAs, quantities related to dust, such as reddening and metallicity, appear to have a greater impact on DIB strengths than does H I gas abundance; the organic molecules, likely responsible for DIBs in DLA-selected sight lines, are underabundant relative to sight lines in the Galaxy of similarly high N(H I). With regard to the study of astrobiology, this could have implications for the abundance of organic molecules in redshifted galaxies. However, since DLAs are observed to have low reddening, selection bias likely plays a role in the apparent underabundance of DIBs in DLAs.
112026797
RADIATION TESTING OF GLAST LAT TRACKER ASICS
122985602
BABAR SILICON VERTEX TRACKER
Abstract A silicon-strip detector tracking system is being constructed for the BaBar experiment at the SLAC B-Factory. The background environment at the B-Factory and the demands imposed by the objective of studying CP violation in the B-meson system lead to a set of requirements and a design that are substantially different from those of existing silicon-strip systems. Those requirements are explained, and a design is presented which is believed to robustly satisfy all of them.
111381772
Eight gamma-ray pulsars discovered in blind frequency searches of Fermi LAT data
We report the discovery of eight gamma-ray pulsars in blind frequency searches using the LAT, onboard the Fermi Gamma-ray Space Telescope. Five of the eight pulsars are young (tau_c 10^36 erg/s), and located within the Galactic plane (|b|<3 deg). The remaining three are older, less energetic, and located off the plane. Five pulsars are associated with sources included in the LAT bright gamma-ray source list, but only one, PSR J1413-6205, is clearly associated with an EGRET source. PSR J1023-5746 has the smallest characteristic age (tau_c=4.6 kyr) and is the most energetic (Edot=1.1E37 erg/s) of all gamma-ray pulsars discovered so far in blind searches. PSRs J1957+5033 and J2055+25 have the largest characteristic ages (tau_c~1 Myr) and are the least energetic (Edot~5E33 erg/s) of the newly-discovered pulsars. We present the timing models, light curves, and detailed spectral parameters of the new pulsars. We used recent XMM observations to identify the counterpart of PSR J2055+25 as XMMU J205549.4+253959. In addition, publicly available archival Chandra X-ray data allowed us to identify the likely counterpart of PSR J1023-5746 as a faint, highly absorbed source, CXOU J102302.8-574606. The large X-ray absorption indicates that this could be among the most distant gamma-ray pulsars detected so far. PSR J1023-5746 is positionally coincident with the TeV source HESS J1023-575, located near the young stellar cluster Westerlund 2, while PSR J1954+2836 is coincident with a 4.3 sigma excess reported by Milagro at a median energy of 35 TeV. Deep radio follow-up observations of the eight pulsars resulted in no detections of pulsations and upper limits comparable to the faintest known radio pulsars, indicating that these can be included among the growing population of radio-quiet pulsars in our Galaxy being uncovered by the LAT, and currently numbering more than 20.
115852024
Measurement of the quantum efficiency of TMAE and TEA from threshold to 120 nm
Several existing and planned high energy physics experiments incorporate detectors which use either TMAE (tetrakis-dimethylaminoethylene) or TEA (triethylamine) as their photosensitive agent. Understanding the operation of these devices requires knowledge of the absolute photoionization quantum efficiencies and absorption lengths of TMAE and TEA. In an experiment performed at the National Synchrotron Light source at Brookhaven National Laboratory, we have measured these parameters from 120 nm to 280 nm. The quantum efficiencies were normalized to the known photoionization yields of benzene and cis-2-butene. The results of these measurements and details of the experiment are presented in this paper.
23177219
Fermi-LAT Sensitivity to Dark Matter Annihilation in Via Lactea II Substructure
We present a study of the ability of the Fermi Gamma-ray Space Telescope to detect dark matter (DM) annihilation signals from the Galactic subhalos predicted by the Via Lactea II N-body simulation. We implement an improved formalism for estimating the boost factor needed to account for the effect of DM clumping on scales below the resolution of the simulation, and we incorporate a detailed Monte Carlo simulation of the response of the Fermi-LAT, including a simulation of its all-sky observing mode integrated over a 10 year mission. We find that for WIMP masses up to about 150 GeV c –2 in standard supersymmetric models with σv = 3 × 10–26 cm3 s–1, a few subhalos could be detectable with >5 standard deviation significance and would likely deviate significantly from the appearance of a point source.