103 research outputs found
Alien Registration- Weisz, Hans (Rumford, Oxford County)
https://digitalmaine.com/alien_docs/13458/thumbnail.jp
Alien Registration Card- Weisz, Hans (Rumford, Oxford County)
https://digitalmaine.com/alien_cards/1136/thumbnail.jp
Signatures of unresolved binaries in stellar spectra: implications for spectral fitting
The observable spectrum of an unresolved binary star system is a
superposition of two single-star spectra. Even without a detectable velocity
offset between the two stellar components, the combined spectrum of a binary
system is in general different from that of either component, and fitting it
with single-star models may yield inaccurate stellar parameters and abundances.
We perform simple experiments with synthetic spectra to investigate the effect
of unresolved main-sequence binaries on spectral fitting, modeling spectra
similar to those collected by the APOGEE, GALAH, and LAMOST surveys. We find
that fitting unresolved binaries with single-star models introduces systematic
biases in the derived stellar parameters and abundances that are modest but
certainly not negligible, with typical systematic errors of in
, 0.1 dex in , and 0.1 dex in for APOGEE-like
spectra of solar-type stars. These biases are smaller for spectra at optical
wavelengths than in the near-infrared. We show that biases can be corrected by
fitting spectra with a binary model, which adds only two labels to the fit and
includes single-star models as a special case. Our model provides a promising
new method to constrain the Galactic binary population, including systems with
single-epoch spectra and no detectable velocity offset between the two stars.Comment: Accept to MNRAS with minor revisions since v1. 7 pages, 5 figure
The M81 Group Dwarf Irregular Galaxy DDO 165. II. Connecting Recent Star Formation with ISM Structures and Kinematics
We compare the stellar populations and complex neutral gas dynamics of the
M81 group dIrr galaxy DDO 165 using data from the HST and the VLA. Paper I
identified two kinematically distinct HI components, multiple localized high
velocity gas features, and eight HI holes and shells (the largest of which
spans ~2.2x1.1 kpc). Using the spatial and temporal information from the
stellar populations in DDO 165, we compare the patterns of star formation over
the past 500 Myr with the HI dynamics. We extract localized star formation
histories within 6 of the 8 HI holes identified in Paper I, as well as 23 other
regions that sample a range of stellar densities and neutral gas properties.
From population synthesis modeling, we derive the energy outputs (from stellar
winds and supernovae) of the stellar populations within these regions over the
last 100 Myr, and compare with refined estimates of the energies required to
create the HI holes. In all cases, we find that "feedback" is energetically
capable of creating the observed structures in the ISM. Numerous regions with
significant energy inputs from feedback lack coherent HI structures but show
prominent localized high velocity gas features; this feedback signature is a
natural product of temporally and spatially distributed star formation. In DDO
165, the extended period of heightened star formation activity (lasting more
than 1 Gyr) is energetically capable of creating the observed holes and high
velocity gas features in the neutral ISM.Comment: The Astrophysical Journal, in press. Full-resolution version
available on request from the first autho
Discovery and Characterization of 3000+ Main-Sequence Binaries from APOGEE Spectra
We develop a data-driven spectral model for identifying and characterizing
spatially unresolved multiple-star systems and apply it to APOGEE DR13 spectra
of main-sequence stars. Binaries and triples are identified as targets whose
spectra can be significantly better fit by a superposition of two or three
model spectra, drawn from the same isochrone, than any single-star model. From
an initial sample of 20,000 main-sequence targets, we identify
2,500 binaries in which both the primary and secondary star contribute
detectably to the spectrum, simultaneously fitting for the velocities and
stellar parameters of both components. We additionally identify and fit
200 triple systems, as well as 700 velocity-variable systems in
which the secondary does not contribute detectably to the spectrum. Our model
simplifies the process of simultaneously fitting single- or multi-epoch spectra
with composite models and does not depend on a velocity offset between the two
components of a binary, making it sensitive to traditionally undetectable
systems with periods of hundreds or thousands of years. In agreement with
conventional expectations, almost all the spectrally-identified binaries with
measured parallaxes fall above the main sequence in the color-magnitude
diagram. We find excellent agreement between spectrally and dynamically
inferred mass ratios for the 600 binaries in which a dynamical mass ratio
can be measured from multi-epoch radial velocities. We obtain full orbital
solutions for 64 systems, including 14 close binaries within hierarchical
triples. We make available catalogs of stellar parameters, abundances, mass
ratios, and orbital parameters.Comment: Accepted to MNRAS with minor revisions since v1. 19 pages, 12
figures, plus Appendice
The M81 Group Dwarf Irregular Galaxy DDO 165. I. High Velocity Neutral Gas in a Post-Starburst System
We present new multi-configuration VLA HI spectral line observations of the
M81 group dIrr post-starburst galaxy DDO 165. The HI morphology is complex,
with multiple column density peaks surrounding a large region of very low HI
surface density that is offset from the center of the stellar distribution. The
bulk of the neutral gas is associated with the southern section of the galaxy;
a secondary peak in the north contains ~15% of the total HI mass. These
components appear to be kinematically distinct, suggesting that either tidal
processes or large-scale blowout have recently shaped the ISM of DDO 165. Using
spatially-resolved position-velocity maps, we find multiple localized
high-velocity gas features. Cross-correlating with radius-velocity analyses, we
identify eight shell/hole structures in the ISM with a range of sizes (~400-900
pc) and expansion velocities (~7-11 km/s). These structures are compared with
narrow- and broad-band imaging from KPNO and HST. Using the latter data, recent
works have shown that DDO 165's previous "burst" phase was extended temporally
(>1 Gyr). We thus interpret the high-velocity gas features, HI holes, and
kinematically distinct components of the galaxy in the context of the immediate
effects of "feedback" from recent star formation. In addition to creating HI
holes and shells, extended star formation events are capable of creating
localized high velocity motion of the surrounding interstellar material. A
companion paper connects the energetics from the HI and HST data.Comment: The Astrophysical Journal, in press. Full-resolution version
available on request from the first autho
The Stellar and Gaseous Contents of the Orion Dwarf Galaxy
We present new KPNO 0.9-m optical and VLA HI spectral line observations of
the Orion dwarf galaxy. This nearby (D ~ 5.4 Mpc), intermediate-mass (M_dyn =
1.1x10^10 Solar masses) dwarf displays a wealth of structure in its neutral
ISM, including three prominent "hole/depression" features in the inner HI disk.
We explore the rich gas kinematics, where solid-body rotation dominates and the
rotation curve is flat out to the observed edge of the HI disk (~6.8 kpc). The
Orion dwarf contains a substantial fraction of dark matter throughout its disk:
comparing the 4.7x10^8 Solar masses of detected neutral gas with estimates of
the stellar mass from optical and near-infrared imaging (3.7x10^8 Solar masses)
implies a mass-to-light ratio of ~13. New H alpha observations show only
modest-strength current star formation (~0.04 Solar masses per year); this star
formation rate is consistent with our 1.4 GHz radio continuum non-detection.Comment: Astronomical Journal, in press. Full-resolution version available
from http://www.macalester.edu/~jcannon/pubs.htm
Worm algorithms for the 3-state Potts model with magnetic field and chemical potential
We discuss worm algorithms for the 3-state Potts model with external field
and chemical potential. The complex phase problem of this system can be
overcome by using a flux representation where the new degrees of freedom are
dimer and monomer variables. Working with this representation we discuss two
different generalizations of the conventional Prokof'ev-Svistunov algorithm
suitable for Monte Carlo simulations of the model at arbitrary chemical
potential and evaluate their performance.Comment: 23 pages, 8 figure
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