Using archival Hubble Space Telescope (HST) imaging data, we report the multiband photometric properties of 13 ultraluminous X-ray sources (ULXs) that have a unique compact optical counterpart. Both magnitude and color variation are detected at timescales of days to years. The optical color, variability, and X-ray to optical flux ratio indicate

Type Ia supernovae are key tools for measuring distances on a cosmic scale. They are generally thought to be the thermonuclear explosion of an accreting white dwarf in a close binary system. The nature of the mass donor is still uncertain. In the single-degenerate model it is a main-sequence star or an evolved star, whereas in the double-degenerate

As part of an ongoing Chandra program for precise localization of X-ray transients in low-mass X-ray binaries, we obtained a short Chandra/ACIS-I observation of the X-ray transient Swift J174535.5-285921 during its 2011 July discovery outburst (ATEL #3472, #3476, #3481, #3508). The exposure time was 966 s, using a (1/8)-subarray of the I3 chip with

As part of an ongoing Chandra program for precise localization of transient low-mass X-ray binaries, we obtained a short Chandra observation of the 401 Hz transient accreting millisecond X-ray pulsar IGR J17498-2921 during its 2011 August discovery outburst (ATEL #3551, #3555, #3556). Our observation was made on 2011 August 22, 00:40 TT with an

The cosmic infrared background (CIB) includes roughly half of the energy radiated by all galaxies at all wavelengths across cosmic time, as observed at the present epoch. The PACS Evolutionary Probe (PEP) survey is exploited here to study the CIB and its redshift differential, at 70, 100 and 160 μm, where the background peaks. Combining PACS

Aims: We present a number of improvements to the MILES library and stellar population models. We correct some small errors in the radial velocities of the stars, measure the spectral resolution of the library and models more accurately, and give a better absolute flux calibration of the models. Methods: We use cross-correlation techniques to