2 research outputs found
Multiplicity Statistics of Stars in the Sagittarius Dwarf Spheroidal Galaxy: Comparison to the Milky Way
We use time-resolved spectra from the Apache Point Observatory Galactic
Evolution Experiment (APOGEE) to examine the distribution of radial velocity
(RV) variations in 249 stars identified as members of the Sagittarius (Sgr)
dwarf spheroidal (dSph) galaxy by Hayes et al (2020). We select Milky Way (MW)
stars that have stellar parameters (, , and ) similar
to those of the Sagittarius members by means of a k-d tree of dimension 3. We
find that the shape of the distribution of RV shifts in Sgr dSph stars is
similar to that measured in their MW analogs, but the total fraction of RV
variable stars in the Sgr dSph is larger by a factor of . After ruling
out other explanations for this difference, we conclude that the fraction of
close binaries in the Sgr dSph is intrinsically higher than in the MW. We
discuss the implications of this result for the physical processes leading to
the formation of close binaries in dwarf spheroidal and spiral galaxies
The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars
We present observations and timing analyses of 68 millisecond pulsars (MSPs)
comprising the 15-year data set of the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav). NANOGrav is a pulsar timing array (PTA)
experiment that is sensitive to low-frequency gravitational waves. This is
NANOGrav's fifth public data release, including both "narrowband" and
"wideband" time-of-arrival (TOA) measurements and corresponding pulsar timing
models. We have added 21 MSPs and extended our timing baselines by three years,
now spanning nearly 16 years for some of our sources. The data were collected
using the Arecibo Observatory, the Green Bank Telescope, and the Very Large
Array between frequencies of 327 MHz and 3 GHz, with most sources observed
approximately monthly. A number of notable methodological and procedural
changes were made compared to our previous data sets. These improve the overall
quality of the TOA data set and are part of the transition to new pulsar timing
and PTA analysis software packages. For the first time, our data products are
accompanied by a full suite of software to reproduce data reduction, analysis,
and results. Our timing models include a variety of newly detected astrometric
and binary pulsar parameters, including several significant improvements to
pulsar mass constraints. We find that the time series of 23 pulsars contain
detectable levels of red noise, 10 of which are new measurements. In this data
set, we find evidence for a stochastic gravitational-wave background.Comment: 90 pages, 74 figures, 6 tables; published in Astrophysical Journal
Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational
Wave Background. For questions or comments, please email
[email protected]