Engineering topics

Leahy, Denis

Publications and source records attributed to Leahy, Denis.

3 records

DOE OSTI2022

Far-ultraviolet to FIR Spectral-energy Distribution Modeling of the Stellar Formation History of the M31 Bulge

M31 is being surveyed at far- and near-ultraviolet with the UVIT telescope on AstroSat. The central bulge of M31 was observed in the N279N (275–280 nm), N219M (200–240 nm), F172M (160–185 nm), F169M (145–175 nm), and F148W (120–180 nm) filters. These images are made publicly available here. The UVIT data are supplemented with Sloan Digital Sky Survey data in optical, Spitzer data in near-infrared and Herschel data in mid- and far-infrared. The resulting far-ultraviolet to IR spectral-energy distributions for the bulge and for 10 subregions, are modeled using combinations of simple stellar populations and with CIGALE models. We find a dominant old (10–12 Gyr) metal-rich ([Z/H] ~ 0.3) population and a younger (600 Myr) solar abundance ([Z/H] ~ 0) population throughout the bulge. For the innermost 120" we find an additional very young (25 Myr) metal-poor ([Z/H] ~ –0.7) population. The results are consistent with the most recent stellar population studies of the bulge, which find the two populations for the whole bulge and a third young population in the innermost bulge.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Far-ultraviolet Variable Sources in M31

The Ultraviolet Imaging Telescope (UVIT) on board the AstroSat observatory has imaged the Andromeda galaxy (M31) from 2017 to 2019 in the far- and near-UV (FUV and NUV) with the high spatial resolution of ≃1″. The survey covered the large sky area of M31 with a set of observations (Fields), each 28′ in diameter. Field 1 was observed in two epochs with the F148W filter, separated by ≃1133 days (≃3.10 yr). The 6.4 kpc diameter Field 1 (at the distance of M31) includes a substantial part of the inner spiral arms of the galaxy. We identify UVIT sources in both epochs of Field 1 and obtain catalogs of sources that are variable in FUV at >3σ and >5σ confidence level. The fraction of FUV-variable sources is higher for brighter sources, and the fraction is higher in the two main spiral arms compared to other areas. This is evidence that a significant fraction of the FUV variables are associated with hot young stars. Source counterparts are found for 42 of the 86 >5σ FUV variables using existing catalogs. The counterparts include 10 star clusters, 6 H II regions, 5 regular or semiregular variables, 6 other variables, and 6 nova or nova candidates. The UVIT FUV–NUV and FUV–FUV color–magnitude diagrams confirm the association of most of the FUV variables with hot young stars. A catalog of UVIT photometry for the variable sources is presented.

47 OTHER INSTRUMENTATION↗

NASA NTRS1998

A Survey of the 30.5 Day Cycle in LMC X-4

LMC X-1 is a high mass X-ray binary system with a 13.5 sec period accreting pulsar n in a 1.4 day orbit. The system displays a super-orbital cycle of X-ray intensity variations repeating every 30.5 days consisting of alternating high and low X-ray flux state . This phenomenon is believed to be caused by a tilted , precessing accretion disk similar to that in Her X-1. We present results of a study of the 30.5 day "long" cycle of LMC X-4 using RXTE observations. The 30.5 day cycle was surveyed with a series of RXTE pointings. We present the resulting lightcurve and compare it to the average lightcurve obtained from the RXTE All SKY Monitor. We show color - color and color-intensity plots as well as representative spectra. The pulse profile evolution across the single High state of LMC X-4 is shown . there is no evidence for a second weaker high state in LMC X-4 unlike that in Her X-1. We compare the properties of the long cycle in LMC X-4 with those in Her X-1.

Scott, Matthew↗