81 research outputs found
Spatially Resolved Spectroscopic Star Formation Histories of Nearby Disks: Hints of Stellar Migration
We use the Mitchell Spectrograph (formerly VIRUS-P) to observe 12 nearby disk
galaxies. We successfully measure ages in the outer disk in six systems. In
three cases (NGC 2684, NGC 6155, and NGC 7437), we find that a downward break
in the disk surface brightness profile corresponds with a change in the
dominant stellar population with the interior being dominated by active star
formation and the exterior having older stellar populations that are best-fit
with star formation histories that decline with time. The observed increase in
average stellar ages beyond a profile break is similar to theoretical models
that predict surface brightness breaks are caused by stellar migration, with
the outer disk being populated from scattered old interior stars. In three more
cases (IC 1132, NGC 4904, and NGC 6691), we find no significant change in the
stellar population as one crosses the break radius. In these galaxies, both the
inner and outer disks are dominated by active star formation and younger
stellar populations. While radial migration can contribute to the stellar
populations beyond the break, it appears more than one mechanism is required to
explain all of our observed stellar profile breaks.Comment: 18 pages, 21 figures. Accepted for publication in Ap
A Panoply of Cepheid Light Curve Templates
We have generated accurate V and I template light curves using a combination
of Fourier decomposition and principal component analysis for a large sample of
Cepheid light curves. Unlike previous studies, we include short period Cepheids
and stars pulsating in the first overtone mode in our analysis. Extensive Monte
Carlo simulations show that our templates can be used to precisely measure
Cepheid magnitudes and periods, even in cases where there are few observational
epochs. These templates are ideal for characterizing serendipitously discovered
Cepheids and can be used in conjunction with surveys such as Pan-Starrs and
LSST where the observational sampling may not be optimized for Cepheids.Comment: 12 pages, 14 figures. Accepted for publication in AJ fixed
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Testing LSST dither strategies for Survey Uniformity and Large-Scale Structure Systematics
The Large Synoptic Survey Telescope (LSST) will survey the southern sky from 2022{2032 with unprecedented detail. Since the observing strategy can lead to artifacts in the data, we investigate the eects of telescope-pointing osets (called dithers) on the r-band coadded 5 depth yielded after the 10-year survey. We analyze this survey depth for several geometric patterns of dithers (e.g.,random, hexagonal lattice, spiral) with amplitude as large as the radius of the LSST eld-of-view, implemented on dierent timescales (per season, per night, per visit). Our results illustrate that per night and per visit dither assignments are more eective than per season. Also, we find that some dither geometries (e.g., hexagonal lattice) are particularly sensitive to the timescale on whichthe dithers are implemented, while others like random dithers perform well on all timescales. We then model the propagation of depth variations to articial uctuations in galaxy counts, which are a systematic for large-scale structure studies. We calculate the bias in galaxy counts caused by the observing strategy, accounting for photometric calibration uncertainties, dust extinction, and magnitude cuts; uncertainties in this bias limit our ability to account for structure induced by the observing strategy. We nd that after 10 years of the LSST survey, the best dither strategies lead to uncertainties in this bias smaller than the minimum statistical floor for a galaxy catalog as deep asr<27.5. A few of these strategies bring the uncertainties close to the statistical floor for r<25.7 after only one year of survey.Fil: Awan, Humna. Rutgers University; Estados UnidosFil: Gawiser, Eric. Rutgers University; Estados UnidosFil: Kurczynski, Peter. Rutgers University; Estados UnidosFil: Lynne Jones, R.. University of Washington; Estados UnidosFil: Zhan, Hu. Chinese Academy of Sciences; República de ChinaFil: Padilla, Nelson David. Pontificia Universidad Católica de Chile; ChileFil: Muñoz Arancibia, Alejandra M.. Pontificia Universidad Católica de Chile; ChileFil: Orsi, Alvaro. Centro de Estudios de Fisica del Cosmos de Aragon; EspañaFil: Cora, Sofia Alejandra. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; ArgentinaFil: Yoachim, Peter. University of Washington; Estados Unido
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