Christopher Thomas Rodgers

Variable Stars in the Newly Discovered Milky Way Satellite in Bootes

We present V, I light curves for 12 variable stars identified in the newly discovered satellite of the Milky Way in the Bootes constellation. Our sample includes 11 RR Lyrae stars (five first overtone, five fundamental mode, and one double-mode pulsator) and one long-period variable close to the galaxy red giant branch tip. The RR Lyrae stars trace very well the average V luminosity of the galaxy horizontal branch, leading to a true distance modulus for the galaxy of μ0 = 19.11 ± 0.08 mag for an assumed metal abundance of [Fe/H] = -2.5 and for E(B - V) = 0.02 mag. Average periods are Pab = 0.69 days and Pc = 0.37 days for ab- and c-type RR Lyrae stars, respectively, making Bootes the second pure Oosterhoff type II (OoII) dSph after Ursa Minor. The location of the double-mode RR Lyrae (RRd) in the Petersen diagram is consistent with RRd stars in OoII clusters and corresponds to an intrinsic luminosity of log L/ log L☉ = 1.72 (for Z = 10-4 and M = 0.80 M☉) according to nonlinear convective pulsation models.

Variable Stars in the Newly Discovered Milky Way Dwarf Spheroidal Satellite Canes Venatici I

We have identified 23 RR Lyrae stars and three possible anomalous Cepheids (ACs) among 84 candidate variables in the recently discovered Canes Venatici I (CVn I) dwarf spheroidal galaxy. The mean period of 18 RRab type stars, --> Pab = 0.60 ± 0.01 days, and the location of these stars in the period-amplitude diagram suggest that CVn I is likely an Oosterhoff-intermediate system. The average apparent magnitude of the RR Lyrae stars, --> V = 22.17 ± 0.02 mag, gives a distance of 210 -->+ 7−5 kpc, for an adopted reddening -->E(B − V) = 0.03 mag. We present a B, V color-magnitude diagram (CMD) of CVn I that reaches -->V ~ 25 mag, and shows that the galaxy has a mainly old stellar population with a metal abundance near [Fe/H] = –2.0 dex. The width of the red giant branch and the location of the candidate ACs on the CMD may indicate that the galaxy hosts a complex stellar population with stars from ~13 Gyr to as young as ~0.6 Gyr.

On the Newly Discovered Canes Venatici II dSph Galaxy

We report on the detection of variable stars in the Canes Venatici II (CVn II) dwarf spheroidal galaxy, a new satellite of the Milky Way recently discovered by the Sloan Digital Sky Survey. We also present a V, -->B − V color-magnitude diagram that reaches -->V ~ 25.5 mag, showing the galaxys main-sequence turnoff at -->V ~ 24.5 mag and revealing several candidate blue straggler stars. Two RR Lyrae stars have been identified within the half-light radius of CVn II, a fundamental-mode variable (RRab) with period -->Pab = 0.743 days, and a first-overtone (RRc) RR Lyrae star with -->Pc = 0.358 days. The rather long periods of these variables along with their position on the period-amplitude diagram support an Oosterhoff type II classification for CVn II. The average apparent magnitude of the RR Lyrae stars, --> V = 21.48 ± 0.02 mag, is used to obtain a precision distance modulus of -->μ0 = 21.02 ± 0.06 mag and a corresponding distance of -->160+ 4−5 kpc, for an adopted reddening -->E(B − V) = 0.015 mag.

Stellar Archaeology in the Milky Way Halo: Variable Stars and Stellar Populations in the New Milky Way Satellites Discovered by the SDSS

We present results of a project devoted to the extensive survey of the ultra‐faint Milky Way dwarf spheroidal satellites recently discovered by the SDSS (Bootes I, Ursa Major II, Coma, Hercules, Canes Venatici I, Canes Venatici II, Leo IV), that we are monitoring for variability using time‐series multiband observations collected at a variety of telescopes from the 1.5 to the 4.3 m size, and reaching each galaxy’s main sequence turnoff In particular, we present results on the pulsation properties and “Oosterhoff type” of the RR Lyrae stars detected in two of the newly discovered dwarf spheroidals, namely Leo IV and Ursa Major II. The variable stars and the stellar populations of these two galaxies are discussed in light of the insight they can provide to reconstruct the star formation history and the merging episodes that led to the early assembly of the Galactic halo.

RR Lyrae stars in the Bootes structure

V, I time-series photometry of the new Milky Way satellite recently discovered in the Bootes constellation (Belokurov et al . 2006) was collected at the TNG, WIRO and Loiano telescopes and used to search for variable stars. We have identified a non-negligible population of RR Lyrae variables, which confirms the presence of an old population in this newly discovered structure. The distribution of periods coupled with information on the evolutionary status of the system derived fromthe color-magnitude diagram provide important hints on the nature and history of this intriguing new companion of the Milky Way.