1,148 research outputs found
Preliminary Abundance Analysis of Galactic Bulge Main Sequence, Subgiant, and Giant Branch Stars Observed During Microlensing with Keck/HIRES
We present an abundance analysis of six main sequence turnoff, subgiant, and
giant branch stars toward the Galactic bulge that were observed with Keck/HIRES
during microlensing events. This is an early look at the first detailed
chemical analysis of main sequence stars in the Galactic bulge. Lensing events
allow the effective aperture of Keck to be increased beyond its current
dimensions; although, some events still stretched its spectroscopic
capabilities. Future large telescopes with high resolution and high throughput
spectrometers will allow the study of abundances in distant stellar populations
and in less evolved stars with greater ease.Comment: 8 pages including 2 figures. To appear in SPIE proceedings on
Astronomical Telescopes and Instrumentation. Uses spie.cl
The Near-Infrared Photometric Properties of Bright Giants in the Central Regions of the Galactic Bulge
Images recorded through broad (J, H, K), and narrow (CO, and 2.2micron
continuum) band filters are used to investigate the photometric properties of
bright (K < 13.5) stars in a 6 x 6 arcmin field centered on the SgrA complex.
The giant branch ridgelines in the (K, J-K) and (K, H-K) color-magnitude
diagrams are well matched by the Baade's Window (BW) M giant sequence if the
mean extinction is A_K ~ 2.8 mag. Extinction measurements for individual stars
are estimated using the M_K versus infrared color relations defined by M giants
in BW, and the majority of stars have A_K between 2.0 and 3.5 mag. The
extinction is locally high in the SgrA complex, where A_K ~ 3.1 mag.
Reddening-corrected CO indices, CO_o, are derived for over 1300 stars with J,
H, and K brightnesses, and over 5300 stars with H and K brightnesses. The
distribution of CO_o values for stars with K_o between 11.25 and 7.25 can be
reproduced using the M_K versus CO_o relation defined by M giants in BW. The
data thus suggest that the most metal-rich giants in the central regions of the
bulge and in BW have similar photometric properties and 2.3micron CO strengths.
Hence, it appears that the central region of the bulge does not contain a
population of stars that are significantly more metal-rich than what is seen in
BW.Comment: 29 pages, including 14 figure
Unraveling the Infrared Transient VVV-WIT-06: The Case for the Origin as a Classical Nova
Indexación: Scopus.E.Y.H. acknowledges the support provided by the National Science Foundation under Grant No. AST-1613472 and by the Florida Space Grant Consortium. L.G. acknowledges support from the FINCA visitor programme. The research work at the Physical Research Laboratory is funded by the Department of Space, Government of India. Facility: Magellan: Baade(FIRE).The enigmatic near-infrared transient VVV-WIT-06 underwent a large-amplitude eruption of unclear origin in 2013 July. Based on its light curve properties and late-time post-outburst spectra, various possibilities have been proposed in the literature for the origin of the object, namely a Type I supernova, a classical nova (CN), or a violent stellar merger event. We show that, of these possibilities, an origin in a CN outburst convincingly explains the observed properties of VVV-WIT-06. We estimate that the absolute K-band magnitude of the nova at maximum was M k = -8.2 ±0.5, its distance d = 13.35 ±2.18 kpc, and the extinction A v = 15.0 ±0.55 mag. © 2018. The American Astronomical Society. All rights reserved.https://iopscience.iop.org/article/10.3847/1538-4357/aae5d
Fabry-Perot Absorption Line Spectroscopy of the Galactic Bar. II. Stellar Metallicities
We measure the Ca II 8542 line strength in 3360 stars along three
lines-of-sight in the Galactic bar: (l,b) ~ (+/-5.0,-3.5) and Baade's Window,
using Fabry-Perot (FP) absorption line spectroscopy. This is the first attempt
to show that reliable absorption line strengths can be measured using FP
spectroscopy. The Ca II 8542 line is a good indicator of metallicity and its
calibration to [Fe/H] is determined for globular cluster red giants in previous
investigations. We derive such a calibration for the bulge giants and use it to
infer metallicities for our full red clump sample (2488 stars) at all three
lines-of-sight. We present the stellar metallicity distributions along the
major axis of the bar. We find the mean [Fe/H] = -0.09 +/- 0.04 dex in Baade's
Window, and find the distribution in this field to agree well with previous
works. We find gradients in the mean metallicity and its dispersion w.r.t
Baade's WIndow of -0.45 and -0.20 dex respectively at l = +5.5, and of -0.10
dex and -0.20 dex at l = -5.0. We detect a signature of a possible tidal stream
at l = +5.5, in both our velocity and metallicity distributions. Its radial
velocity indicates that it is not associated with the Sagittarius stream. We
also measure the metallicity of a bulge globular cluster NGC 6522 in our
Baade's Window field to be -0.90 +/- 0.10 dex, in agreement with recent
measurements of Zoccali et al. (2008). This agreement demonstrates the
reliability of our metallicity measurements.Comment: accepted for publication in the Astrophysical Journal, 15 pages, 12
figure
Millimagnitude Photometry for Transiting Extrasolar Planetary Candidates. V. Follow-up of 30 OGLE Transits. New Candidates
We used VLT/VIMOS images in the V band to obtain light curves of extrasolar
planetary transits OGLE-TR-111 and OGLE-TR-113, and candidate planetary
transits: OGLE-TR-82, OGLE-TR-86, OGLE-TR-91, OGLE-TR-106, OGLE-TR-109,
OGLE-TR-110, OGLE-TR-159, OGLE-TR-167, OGLE-TR-170, OGLE-TR-171. Using
difference imaging photometry, we were able to achieve millimagnitude errors in
the individual data points. We present the analysis of the data and the light
curves, by measuring transit amplitudes and ephemerides, and by calculating
geometrical parameters for some of the systems. We observed 9 OGLE objects at
the predicted transit moments. Two other transits were shifted in time by a few
hours. For another seven objects we expected to observe transits during the
VIMOS run, but they were not detected. The stars OGLE-TR-111 and OGLE-TR-113
are probably the only OGLE objects in the observed sample to host planets, with
the other objects being very likely eclipsing binaries or multiple systems. In
this paper we also report on four new transiting candidates which we have found
in the data.Comment: 11 pages, 17 figures, accepted for publication in A&
Extragalactic Globular Clusters in the Near-Infrared II. The Globular Clusters Systems of NGC 3115 and NGC 4365
We combine near-infrared photometry obtained with the VLT/ISAAC instrument
and archival HST/WFPC2 optical images to determine VIK magnitudes and colours
of globular clusters in two early-type galaxies, NGC 3115 and NGC 4365. The
combination of near-IR and optical photometry provides a way to lift the
age-metallicity degeneracy. For NGC 3115, the globular cluster colours reveal
two major sub-populations, consistent with previous studies. By comparing the
V-I, V-K colours of the NGC 3115 globular clusters with SSP models, we find
that the colour difference between the two >10 Gyr old major sub-populations is
primarily due to a difference in metallicity. We find \Delta[Fe/H] = 1.0 +/-
0.3 dex and the blue and red globular cluster sub-populations being coeval
within 3 Gyr. In contrast to the NGC 3115 globular clusters, the globular
cluster system in NGC 4365 exhibits a more complex age and metallicity
structure. We find a significant population of intermediate-age very metal-rich
globular clusters along with an old population of both metal-rich and
metal-poor clusters. Specifically, we observe a large population of globular
clusters with V-K and V-I colours, for which all current SSP models give ages
and metallicities in the range ~2-8 Gyr and ~0.5-3 Z_solar, respectively. After
10 Gyr of passive evolution, the intermediate-age globular clusters in NGC 4365
will have colours which are consistent with the very metal-rich population of
globular clusters in giant elliptical galaxies, such as M87. Our results for
both globular cluster systems are consistent with previous age and metallicity
studies of the diffuse galactic light. In addition to the major globular
cluster populations in NGC 3115 and NGC 4365 we report on the detection of
objects with extremely red colours.Comment: accepted for publication in A&A, 19 pages, incl. 9 figure
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