73 research outputs found
The Metallicity of the Monoceros Stream
We present low-resolution MMT Hectospec spectroscopy of 594 candidate
Monoceros stream member stars. Based on strong color-magnitude diagram
overdensities, we targeted three fields within the stream's footprint, with 178
deg < l < 203 deg and -25 deg < b < 25 deg. By comparing the measured iron
abundances with those expected from smooth Galactic components alone, we
measure, for the first time, the spectroscopic metallicity distribution
function for Monoceros. We find the stream to be chemically distinct from both
the thick disk and halo, with [Fe/H] = -1, and do not detect a trend in the
stream's metallicity with Galactic longitude. Passing from b = +25 deg to b =
-25 deg the median Monoceros metallicity trends upward by 0.1 dex, though
uncertainties in modeling sample contamination by the disk and halo make this a
marginal detection. In each field, we find Monoceros to have an intrinsic
[Fe/H] dispersion of 0.10-0.22 dex. From the CaII K line, we measure [Ca/Fe]
for a subsample of metal poor program stars with -1.1 < [Fe/H] < -0.5. In two
of three fields, we find calcium deficiencies qualitatively similar to
previously reported [Ti/Fe] underabundances in Monoceros and the Sagittarius
tidal stream. Further, using 90 spectra of thick disk stars in the Monoceros
pointings with b ~ +/-25 deg, we detect a 0.22 dex north/south metallicity
asymmetry coincident with known stellar density asymmetry at R_GC ~ 12 kpc and
|Z| ~ 1.7 kpc. Our median Monoceros [Fe/H] = -1.0 and its relatively low
dispersion naturally fit the expectation for an appropriately luminous M_V ~
-13 dwarf galaxy progenitor.Comment: accepted for publication in Ap
Jupiter's Metastable Companions
Jovian co-orbitals share Jupiter's orbit in 1:1 mean motion resonance. This
includes 10,000 so-called Trojan asteroids surrounding the leading (L4) and
trailing (L5) Lagrange points, viewed as stable groups dating back to planet
formation. Via a massive numerical study we identify for the first time some
Trojans which are certainly only `metastable'; instead of being primordial,
they are recent captures from heliocentric orbits into moderately long-lived
(10 kyr - 100 Myr) metastable states that will escape back to the scattering
regime. We have also identified (1) the first two jovian horseshoe co-orbitals
that exist for many resonant libration periods, and (2) eight jovian
quasi-satellites with metastable lifetimes of 4-130 kyr. Our perspective on the
Trojan population is thus now more complex as Jupiter joins the other giant
planets in having known metastable co-orbitals which are in steady-state
equilibrium with the planet-crossing Centaur and asteroid populations, in
agreement with theoretical estimates
Tidal Synchronization and Differential Rotation of Kepler Eclipsing Binaries
Few observational constraints exist for the tidal synchronization rate of
late-type stars, despite its fundamental role in binary evolution. We visually
inspected the light curves of 2278 eclipsing binaries (EBs) from the Kepler
Eclipsing Binary Catalog to identify those with starspot modulations, as well
as other types of out-of-eclipse variability. We report rotation periods for
816 EBs with starspot modulations, and find that 79% of EBs with orbital
periods less than ten days are synchronized. However, a population of short
period EBs exists with rotation periods typically 13% slower than synchronous,
which we attribute to the differential rotation of high latitude starspots. At
10 days, there is a transition from predominantly circular, synchronized EBs to
predominantly eccentric, pseudosynchronized EBs. This transition period is in
good agreement with the predicted and observed circularization period for Milky
Way field binaries. At orbital periods greater than about 30 days, the amount
of tidal synchronization decreases. We also report 12 previously unidentified
candidate Scuti and Doradus pulsators, as well as a candidate
RS CVn system with an evolved primary that exhibits starspot occultations. For
short period contact binaries, we observe a period-color relation, and compare
it to previous studies. As a whole, these results represent the largest
homogeneous study of tidal synchronization of late-type stars.Comment: Accepted for publication in the Astronomical Journal. EB rotation
periods and classifications available at
https://github.com/jlurie/decatur/blob/master/decatur/data/final_catalog.cs
Agile software development in an earned value world: a survival guide
Agile methodologies are current best practice in software development. They are favored for, among other reasons, preventing premature optimization by taking a somewhat short-term focus, and allowing frequent replans/reprioritizations of upcoming development work based on recent results and current backlog. At the same time, funding agencies prescribe earned value management accounting for large projects which, these days, inevitably include substantial software components. Earned Value approaches emphasize a more comprehensive and typically longer-range plan, and tend to characterize frequent replans and reprioritizations as indicative of problems. Here we describe the planning, execution and reporting framework used by the LSST Data Management team, that navigates these opposite tensions
Radio Astronomy in LSST Era
A community meeting on the topic of "Radio Astronomy in the LSST Era" was
hosted by the National Radio Astronomy Observatory in Charlottesville, VA (2013
May 6--8). The focus of the workshop was on time domain radio astronomy and sky
surveys. For the time domain, the extent to which radio and visible wavelength
observations are required to understand several classes of transients was
stressed, but there are also classes of radio transients for which no visible
wavelength counterpart is yet known, providing an opportunity for discovery.
From the LSST perspective, the LSST is expected to generate as many as 1
million alerts nightly, which will require even more selective specification
and identification of the classes and characteristics of transients that can
warrant follow up, at radio or any wavelength. The LSST will also conduct a
deep survey of the sky, producing a catalog expected to contain over 38 billion
objects in it. Deep radio wavelength sky surveys will also be conducted on a
comparable time scale, and radio and visible wavelength observations are part
of the multi-wavelength approach needed to classify and understand these
objects. Radio wavelengths are valuable because they are unaffected by dust
obscuration and, for galaxies, contain contributions both from star formation
and from active galactic nuclei. The workshop touched on several other topics,
on which there was consensus including the placement of other LSST "Deep
Drilling Fields," inter-operability of software tools, and the challenge of
filtering and exploiting the LSST data stream. There were also topics for which
there was insufficient time for full discussion or for which no consensus was
reached, which included the procedures for following up on LSST observations
and the nature for future support of researchers desiring to use LSST data
products.Comment: Conference summary, 29 pages, 1 figure; to be published in the Publ.
Astron. Soc. Pacific; full science program and presentations available at
http://science.nrao.edu/science/event/RALSST201
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