The Infrared Massive Stellar Content of M83

We present an analysis of archival Spitzer images and new ground-based and Hubble Space Telescope (HST) near-infrared (IR) and optical images of the field of M83 with the goal of identifying rare, dusty, evolved massive stars. We present point source catalogs consisting of 3778 objects from $Spitzer$ Infrared Array Camera (IRAC) Band 1 (3.6 $\mu$m) and Band 2 (4.5 $\mu$m), and 975 objects identified in Magellan 6.5m FourStar near-IR $J$ and $K_{\rm s}$ images. A combined catalog of coordinate matched near- and mid-IR point sources yields 221 objects in the field of M83. Using this photometry we identify 185 massive evolved stellar candidates based on their location in color-magnitude and color-color diagrams. We estimate the background contamination to our stellar candidate lists and further classify candidates based on their appearance in $HST$ Wide Field Camera 3 (WFC3) observations of M83. We find 49 strong candidates for massive stars which are very promising objects for spectroscopic follow-up. Based on their location in a $B-V$ versus $V-I$ diagram, we expect at least 24, or roughly 50%, to be confirmed as red supergiants.Comment: 32 pages, 23 figures, accepted for publication in A&

Variable stars in the globular cluster M28 (NGC 6626)

We present a new search for variable stars in the Galactic globular cluster M28 (NGC 6626). The search is based on a series of BVI images obtained with the SMARTS Consortium's 1.3m telescope at Cerro Tololo Inter-American Observatory, Chile. The search was carried out using the ISIS v2.2 image subtraction package. We find a total of 25 variable stars in the field of the cluster, 9 being new discoveries. Of the newly found variables, 1 is an ab-type RR Lyrae star, 6 are c-type RR Lyrae, and 2 are long-period/semi-regular variables. V22, previously classified as a type II Cepheid, appears as a bona-fide RRc in our data. In turn, V20, previously classified as an ab-type RR Lyrae, could not be properly phased with any reasonable period. The properties of the ab-type RR Lyrae stars in M28 appear most consistent with an Oosterhoff-intermediate classification, which is unusual for bona-fide Galactic globulars clusters. However, the cluster's c-type variables do not clearly support such an Oosterhoff type, and a hybrid Oosterhoff I/II system is accordingly another possibility, thus raising the intriguing possibility of multiple populations being present in M28. Coordinates, periods, and light curves in differential fluxes are provided for all the detected variables.Comment: A&A, in pres

Optical observations of the luminous Type IIn Supernova 2010jl for over 900 days

The luminous Type IIn Supernova (SN) 2010jl shows strong evidence for the interaction of the SN ejecta with dense circumstellar material (CSM). We present observations of SN 2010jl for $t \sim 900$ d after its earliest detection, including a sequence of optical spectra ranging from $t = 55$ to $909$ d. We also supplement our late time spectra and the photometric measurements in the literature with an additional epoch of new, late time $BVRI$ photometry. Combining available photometric and spectroscopic data, we derive a semi-bolometric optical light curve and calculate a total radiated energy in the optical for SN 2010jl of $\sim 3.5\times10^{50}$ erg. We also examine the evolution of the H$\alpha$ emission line profile in detail and find evidence for asymmetry in the profile for $t \gtrsim 775$ d that is not easily explained by any of the proposed scenarios for this fascinating event. Finally, we discuss the interpretations from the literature of the optical and near-infrared light curves, and propose that the most likely explanation of their evolution is the formation of new dust in the dense, pre-existing CSM wind after $\sim 300$ d.Comment: 14 pages, 10 figures, 5 tables. Full version of Table 3 is included as an ancillary fil

Nesting Induced Peierls-type Instability for Compressed Li-CI16

Alkalies are considered to be simple metals at ambient conditions. However, recently reported theoretical and experimental results have shown an unexpected and intriguing correlation between complex structures and an enhanced superconducting transition temperature in lithium under pressure. In this article we analyze the pressure induced Fermi surface deformation in bcc lithium, and its relation to the observed cI16 structure. According to our calculations, the Fermi surface becomes increasingly anisotropic with pressure and develops an extended nesting along the bcc [121] direction. This nesting induces a phonon instability of both transverse modes at N, so that a Peierls-type mechanism is proposed to explain the stability of Li-cI16.Comment: Proceedings of Fukuoka 2006 Conference on Novel Pressure-induced Phenomena in Condensed Matter Systems. To be published in J. Phys. Soc. Jpn. 2 pages and 3 figure