320 research outputs found
Characterizing the Rigidly Rotating Magnetosphere Stars HD 345439 and HD 23478
The SDSS III APOGEE survey recently identified two new Ori E type
candidates, HD 345439 and HD 23478, which are a rare subset of rapidly rotating
massive stars whose large (kGauss) magnetic fields confine circumstellar
material around these systems. Our analysis of multi-epoch photometric
observations of HD 345439 from the KELT, SuperWASP, and ASAS surveys reveals
the presence of a 0.7701 day period in each dataset, suggesting the
system is amongst the faster known Ori E analogs. We also see clear
evidence that the strength of H-alpha, H I Brackett series lines, and He I
lines also vary on a 0.7701 day period from our analysis of multi-epoch,
multi-wavelength spectroscopic monitoring of the system from the APO 3.5m
telescope. We trace the evolution of select emission line profiles in the
system, and observe coherent line profile variability in both optical and
infrared H I lines, as expected for rigidly rotating magnetosphere stars. We
also analyze the evolution of the H I Br-11 line strength and line profile in
multi-epoch observations of HD 23478 from the SDSS-III APOGEE instrument. The
observed periodic behavior is consistent with that recently reported by Sikora
and collaborators in optical spectra.Comment: Accepted in ApJ
the SDSS-III APOGEE Spectral Line List for H-Band Spectroscopy
We present the H-band spectral line lists adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The APOGEE line lists comprise astrophysical, theoretical, and laboratory sources from the literature, as well as newly evaluated astrophysical oscillator strengths and damping parameters. We discuss the construction of the APOGEE line list, which is one of the critical inputs for the APOGEE Stellar Parameters and Chemical Abundances Pipeline, and present three different versions that have been used at various stages of the project. The methodology for the newly calculated astrophysical line lists is reviewed. The largest of these three line lists contains 134,457 molecular and atomic transitions. In addition to the format adopted to store the data, the line lists are available in MOOG, Synspec, and Turbospectrum formats. The limitations of the line lists along with guidance for its use on different spectral types are discussed. We also present a list of H-band spectral features that are either poorly represented or completely missing in our line list. This list is based on the average of a large number of spectral fit residuals for APOGEE observations spanning a wide range of stellar parameters.Alfred P. Sloan FoundationNational Science FoundationU.S. Department of Energy Office of ScienceJanos Bolyai Research Scholarship of the Hungarian Academy of SciencesSpanish Ministry of Economy and Competitiveness AYA-2011-27754, AYA-2014-58082-PRSF 14-50-00043McDonald Observator
APOGEE DR14/DR15 Abundances in the Inner Milky Way
We present an overview of the distributions of 11 elemental abundances in the
Milky Way's inner regions, as traced by APOGEE stars released as part of SDSS
Data Release 14/15 (DR14/DR15), including O, Mg, Si, Ca, Cr, Mn, Co, Ni, Na,
Al, and K. This sample spans ~4000 stars with R_GC<4 kpc, enabling the most
comprehensive study to date of these abundances and their variations within the
innermost few kiloparsecs of the Milky Way. We describe the observed abundance
patterns ([X/Fe]-[Fe/H]), compare to previous literature results and to
patterns in stars at the solar Galactic radius, and discuss possible trends
with DR14/DR15 effective temperatures. We find that the position of the
[Mg/Fe]-[Fe/H] "knee" is nearly constant with R_GC, indicating a well-mixed
star-forming medium or high levels of radial migration in the early inner
Galaxy. We quantify the linear correlation between pairs of elements in
different subsamples of stars and find that these relationships vary; some
abundance correlations are very similar between the alpha-rich and alpha-poor
stars, but others differ significantly, suggesting variations in the
metallicity dependencies of certain supernova yields. These empirical trends
will form the basis for more detailed future explorations and for the
refinement of model comparison metrics. That the inner Milky Way abundances
appear dominated by a single chemical evolutionary track and that they extend
to such high metallicities underscore the unique importance of this part of the
Galaxy for constraining the ingredients of chemical evolution modeling and for
improving our understanding of the evolution of the Galaxy as a whole.Comment: Submitted to AAS Journals; revised after referee repor
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