2dF-AAOmega spectroscopy of massive stars in the Magellanic Clouds: The north-eastern region of the Large Magellanic Cloud

We present spectral classifications from optical spectroscopy of 263 massive stars in the north-eastern region of the Large Magellanic Cloud. The observed two-degree field includes the massive 30 Doradus star-forming region, the environs of SN1987A, and a number of star-forming complexes to the south of 30 Dor. These are the first classifications for the majority (203) of the stars and include eleven double-lined spectroscopic binaries. The sample also includes the first examples of early OC-type spectra (AAOmega 30 Dor 248 and 280), distinguished by the weakness of their nitrogen spectra and by C IV 4658 emission. We propose that these stars have relatively unprocessed CNO abundances compared to morphologically normal O-type stars, indicative of an earlier evolutionary phase. From analysis of observations obtained on two consecutive nights, we present radial-velocity estimates for 233 stars, finding one apparent single-lined binary and nine (>3sigma) outliers compared to the systemic velocity; the latter objects could be runaway stars or large-amplitude binary systems and further spectroscopy is required to investigate their nature.Comment: Accepted by A&

Mapping atomic and diffuse interstellar band absorption across the Magellanic Clouds and the Milky Way

Diffuse interstellar bands (DIBs) trace warm neutral and weakly-ionized diffuse interstellar medium (ISM). Here we present a dedicated, high signal-to-noise spectroscopic study of two of the strongest DIBs, at 5780 and 5797 \AA, in optical spectra of 666 early-type stars in the Small and Large Magellanic Clouds, along with measurements of the atomic Na\,{\sc i}\,D and Ca\,{\sc ii}\,K lines. The resulting maps show for the first time the distribution of DIB carriers across large swathes of galaxies, as well as the foreground Milky Way ISM. We confirm the association of the 5797 \AA\ DIB with neutral gas, and the 5780 \AA\ DIB with more translucent gas, generally tracing the star-forming regions within the Magellanic Clouds. Likewise, the Na\,{\sc i}\,D line traces the denser ISM whereas the Ca\,{\sc ii}\,K line traces the more diffuse, warmer gas. The Ca\,{\sc ii}\,K line has an additional component at $\sim200$--220 km s$^{-1}$ seen towards both Magellanic Clouds; this may be associated with a pan-Magellanic halo. Both the atomic lines and DIBs show sub-pc-scale structure in the Galactic foreground absorption; the 5780 and 5797 \AA\ DIBs show very little correlation on these small scales, as do the Ca\,{\sc ii}\,K and Na\,{\sc i}\,D lines. This suggests that good correlations between the 5780 and 5797 \AA\ DIBs, or between Ca\,{\sc ii}\,K and Na\,{\sc i}\,D, arise from the superposition of multiple interstellar structures. Similarity in behaviour between DIBs and Na\,{\sc i} in the SMC, LMC and Milky Way suggests the abundance of DIB carriers scales in proportion to metallicity.Comment: Accepted for publication in MNRA

RR LYRAE VARIABLE STARS: PULSATIONAL CONSTRAINTS RELEVANT TO THE OOSTERHOFF CONTROVERSY

A solution to the old Oosterhoff controversy is proposed on the basis of a new theoretical pulsational scenario concerning RR Lyrae cluster variables (Bono and coworkers). We show that the observed constancy of the lowest pulsation period in both Oosterhoff type I (OoI) and Oosterhoff type II (OoII) prototypes (M3, M15) can be easily reproduced only by assuming the canonical evolutionary horizontal-branch luminosity levels of these Galactic globular clusters and therefore by rejecting the Sandage period shift effect (SPSE).Comment: postscript file of 7 pages and 2 figures; one non postcript figure is available upon request; for any problem please write to [email protected]

Hunting for planets in the HL Tau disk

Recent ALMA images of HL Tau show gaps in the dusty disk that may be caused by planetary bodies. Given the young age of this system, if confirmed, this finding would imply very short timescales for planet formation, probably in a gravitationally unstable disk. To test this scenario, we searched for young planets by means of direct imaging in the L'-band using the Large Binocular Telescope Interferometer mid-infrared camera. At the location of two prominent dips in the dust distribution at ~70AU (~0.5") from the central star we reach a contrast level of ~7.5mag. We did not detect any point source at the location of the rings. Using evolutionary models we derive upper limits of ~10-15MJup at <=0.5-1Ma for the possible planets. With these sensitivity limits we should have been able to detect companions sufficiently massive to open full gaps in the disk. The structures detected at mm-wavelengths could be gaps in the distributions of large grains on the disk midplane, caused by planets not massive enough to fully open gaps. Future ALMA observations of the molecular gas density profile and kinematics as well as higher contrast infrared observations may be able to provide a definitive answer.Comment: Accepted for publication on ApJ Letter

Clustering in 18O - absolute determination of branching ratios via high-resolution particle spectroscopy

The determination of absolute branching ratios for high-energy states in light nuclei is an important and useful tool for probing the underlying nuclear structure of individual resonances: for example, in establishing the tendency of an excited state towards α -cluster structure. Difficulty arises in measuring these branching ratios due to similarities in available decay channels, such as ( 18 O, n ) and ( 18 O, 2 n ), as well as differences in geometric efficiencies due to population of bound excited levels in daughter nuclei. Methods are presented using Monte Carlo techniques to overcome these issues

The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda VI

We have surveyed Andromeda VI, a dwarf spheroidal galaxy companion to M31, for variable stars using F450W and F555W observations obtained with the Hubble Space Telescope. A total of 118 variables were found, with 111 being RR Lyrae, 6 anomalous Cepheids, and 1 variable we were unable to classify. We find that the Andromeda VI anomalous Cepheids have properties consistent with those of anomalous Cepheids in other dwarf spheroidal galaxies. We revise the existing period-luminosity relations for these variables. Further, using these and other available data, we show that there is no clear difference between fundamental and first-overtone anomalous Cepheids in a period-amplitude diagram at shorter periods, unlike the RR Lyrae. For the Andromeda VI RR Lyrae, we find that they lie close to the Oosterhoff type I Galactic globular clusters in the period-amplitude diagram, although the mean period of the RRab stars, = 0.588 d, is slightly longer than the typical Oosterhoff type I cluster. The mean V magnitude of the RR Lyrae in Andromeda VI is 25.29+/-0.03, resulting in a distance 815+/-25 kpc on the Lee, Demarque, & Zinn distance scale. This is consistent with the distance derived from the I magnitude of the tip of the red giant branch. Similarly, the properties of the RR Lyrae indicate a mean abundance for Andromeda VI which is consistent with that derived from the mean red giant branch color.Comment: 23 pages, including 13 figures and 6 tables, emulateapj5/apjfonts style. Accepted by the Astronomical Journal. We recommend the interested reader to download the preprint with full-resolution figures, which can be found at http://www.noao.edu/noao/staff/pritzl/M31dwarfs.htm

RR Lyrae Stars in the Bootes dSph

We present a catalog of 15 RR Lyrae variable stars in the recently discovered Bootes galaxy -- the most metal-poor simple stellar population with measured RR Lyrae stars. The pulsational properties of the RR Lyrae conform closely to period-abundance trends extrapolated from more metal-rich populations and we estimate the distance of Bootes to be (m-M)_0=18.96+-0.12. The average period (0.69 days), the ratio of type c to type ab pulsators (0.53) and the RRab period shift (-0.07) indicate an Oosterhoff II classification for Bootes, a marked contrast to the other dSph galaxies, which are Oosterhoff intermediate. This supports the contention that the Oosterhoff dichotomy is a continuum -- that RR Lyrae properties, to first order, vary smoothly with abundance. The dSph galaxies are not distinct from the Galactic globular clusters, but bridge the Oosterhoff gap. The absence of any anomalous Cepheids in Bootes could indicate the lack of an intermediate age population.Comment: 16 pages, submitted to Astrophysical Journal Letter