333 research outputs found
A rare telson anomaly in \u3cem\u3eParabuthus liosoma\u3c/em\u3e (Ehrenberg, 1828) (Scorpiones: Buthidae)
A rare anomaly of telson vesicle with two functional aculei is observed and discussed in a Parabuthus liosoma (Ehrenberg, 1828) specimen collected from Jizan, Saudi Arabia
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
Breathing FIRE: How Stellar Feedback Drives Radial Migration, Rapid Size Fluctuations, and Population Gradients in Low-Mass Galaxies
We examine the effects of stellar feedback and bursty star formation on
low-mass galaxies ()
using the FIRE (Feedback in Realistic Environments) simulations. While previous
studies emphasized the impact of feedback on dark matter profiles, we
investigate the impact on the stellar component: kinematics, radial migration,
size evolution, and population gradients. Feedback-driven outflows/inflows
drive significant radial stellar migration over both short and long timescales
via two processes: (1) outflowing/infalling gas can remain star-forming,
producing young stars that migrate within their first , and (2) gas outflows/inflows drive strong fluctuations in the
global potential, transferring energy to all stars. These processes produce
several dramatic effects. First, galaxies' effective radii can fluctuate by
factors of over , and these rapid size fluctuations
can account for much of the observed scatter in radius at fixed
Second, the cumulative effects of many outflow/infall episodes steadily heat
stellar orbits, causing old stars to migrate outward most strongly. This
age-dependent radial migration mixes---and even inverts---intrinsic age and
metallicity gradients. Thus, the galactic-archaeology approach of calculating
radial star-formation histories from stellar populations at can be
severely biased. These effects are strongest at , the same regime where feedback most
efficiently cores galaxies. Thus, detailed measurements of stellar kinematics
in low-mass galaxies can strongly constrain feedback models and test baryonic
solutions to small-scale problems in CDM.Comment: Accepted to ApJ (820, 131) with minor revisions from v1. Figure 4 now
includes dark matter. Main results in Figures 7 and 1
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
Evolution of supernovae-driven superbubbles with conduction and cooling
We use spherically symmetric hydrodynamic simulations to study the dynamical
evolution and internal structure of superbubbles (SBs) driven by clustered
supernovae (SNe), focusing on the effects of thermal conduction and cooling in
the interface between the hot bubble interior and cooled shell. Our simulations
employ an effective diffusivity to account for turbulent mixing from nonlinear
instabilities that are not captured in 1D. The conductive heat flux into the
shell is balanced by a combination of cooling in the interface and evaporation
of shell gas into the bubble interior. This evaporation increases the density,
and decreases the temperature, of the SB interior by more than an order of
magnitude relative to simulations without conduction. However, most of the
energy conducted into the interface is immediately lost to cooling, reducing
the evaporative mass flux required to balance conduction. As a result, the
evaporation rate is typically a factor of 3-30 lower than predicted by
the classical similarity solution of Weaver et al. (1977), which neglects
cooling. Blast waves from the first 30 SNe remain supersonic in the SB
interior because reduced evaporation from the interface lowers the mass they
sweep up in the hot interior. Updating the Weaver solution to include cooling,
we construct a new analytic model to predict the cooling rate, evaporation
rate, and temporal evolution of SBs. The cooling rate, and hence the hot gas
mass, momentum, and energy delivered by SBs, is set by the ambient ISM density
and the efficiency of nonlinear mixing at the bubble/shell interface.Comment: 26 pages, 14 figures, plus appendices. Accepted to MNRA
Analyzing white dwarf + white dwarf binaries with Gaia trigonometric parallaxes
White dwarfs (WDs) have been used as chronometers to age date the solar neighborhood, open clusters, globular clusters, and even the Galactic halo field population. The availability of highly accurate and precise Gaia trigonometric parallaxes along with nearly all-sky, homogenous photometric surveys (SDSS, Pan-STARRS) now allows us to improve the precision in WD ages. We report on the consistency of ages among seven WD+WD binaries, run through BASE-9 individually and in pairs. BASE-9 uses Bayesian analysis to estimate the values for stellar parameters, such as age, distance, and metallicity. We found that using Gaia\u27s parallaxes with binary systems constrains the errors in these estimations, by lowering uncertainties and constraining the ages and distances of the systems
- …