26 research outputs found
Implications for the Formation of Blue Straggler Stars from HST Ultraviolet Observations of NGC 188
We present results of a Hubble Space Telescope far-ultraviolet (FUV) survey
searching for white dwarf (WD) companions to blue straggler stars (BSSs) in
open cluster NGC 188. The majority of NGC 188 BSSs (15 of 21) are single-lined
binaries with properties suggestive of mass-transfer formation via Roche lobe
overflow, specifically through an asymptotic giant branch star transferring
mass to a main sequence secondary, yielding a BSS binary with a WD companion.
In NGC 188, a BSS formed by this mechanism within the past 400 Myr will have a
WD companion hot and luminous enough to be directly detected as a FUV
photometric excess with HST. Comparing expected BSS FUV emission to observed
photometry reveals four BSSs with WD companions above 12,000 K (younger than
250 Myr) and three WD companions with temperatures between 11,000-12,000 K.
These BSS+WD binaries all formed through recent mass transfer. The location of
the young BSSs in an optical color-magnitude diagram (CMD) indicates that
distance from the zero-age main sequence does not necessarily correlate with
BSS age. There is no clear CMD separation between mass transfer-formed BSSs and
those likely formed through other mechanisms, such as collisions. The seven
detected WD companions place a lower limit on the mass-transfer formation
frequency of 33%. We consider other possible formation mechanisms by comparing
properties of the BSS population to theoretical predictions. We conclude that
14 BSS binaries likely formed from mass transfer, resulting in an inferred
mass-transfer formation frequency of approximately 67%.Comment: 13 pages, 6 figures, accepted to the Astrophysical Journa
Detection of white dwarf companions to blue stragglers in the open cluster NGC 188: direct evidence for recent mass transfer
Several possible formation pathways for blue straggler stars have been
developed recently, but no one pathway has yet been observationally confirmed
for a specific blue straggler. Here we report the first findings from a Hubble
Space Telescope ACS/SBC far-UV photometric program to search for white dwarf
companions to blue straggler stars. We find three hot and young white dwarf
companions to blue straggler stars in the 7-Gyr open cluster NGC 188,
indicating that mass transfer in these systems ended less than 300 Myr ago.
These companions are direct and secure observational evidence that these blue
straggler stars were formed through mass transfer in binary stars. Their
existence in a well-studied cluster environment allows for observational
constraints of both the current binary system and the progenitor binary system,
mapping the entire mass transfer history.Comment: 5 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
Wolf 1130: A Nearby Triple System Containing a Cool, Ultramassive White Dwarf
Following the discovery of the T8 subdwarf WISEJ200520.38+542433.9 (Wolf
1130C), with common proper motion to a binary (Wolf 1130AB) consisting of an M
subdwarf and a white dwarf, we set out to learn more about the old binary in
the system. We find that the A and B components of Wolf 1130 are tidally
locked, which is revealed by the coherence of more than a year of V band
photometry phase folded to the derived orbital period of 0.4967 days. Forty new
high-resolution, near-infrared spectra obtained with the Immersion Grating
Infrared Spectrometer (IGRINS) provide radial velocities and a projected
rotational velocity (v sin i) of 14.7 +/- 0.7 km/s for the M subdwarf. In
tandem with a Gaia parallax-derived radius and verified tidal-locking, we
calculate an inclination of i=29 +/- 2 degrees. From the single-lined orbital
solution and the inclination we derive an absolute mass for the unseen primary
(1.24+0.19-0.15 Msun). Its non-detection between 0.2 and 2.5 microns implies
that it is an old (>3.7 Gyr) and cool (Teff<7000K) ONe white dwarf. This is the
first ultramassive white dwarf within 25pc. The evolution of Wolf 1130AB into a
cataclysmic variable is inevitable, making it a potential Type Ia supernova
progenitor. The formation of a triple system with a primary mass >100 times the
tertiary mass and the survival of the system through the common-envelope phase,
where ~80% of the system mass was lost, is remarkable. Our analysis of Wolf
1130 allows us to infer its formation and evolutionary history, which has
unique implications for understanding low-mass star and brown dwarf formation
around intermediate mass stars.Comment: 37 pages, 9 Figures, 5 Table
Effective Temperatures of Low-Mass Stars from High-Resolution H-band Spectroscopy
High-resolution, near-infrared spectra will be the primary tool for finding
and characterizing Earth-like planets around low-mass stars. Yet, the
properties of exoplanets can not be precisely determined without accurate and
precise measurements of the host star. Spectra obtained with the Immersion
GRating INfrared Spectrometer (IGRINS) simultaneously provide diagnostics for
most stellar parameters, but the first step in any analysis is the
determination of the effective temperature. Here we report the calibration of
high-resolution H-band spectra to accurately determine effective temperature
for stars between 4000-3000 K (K8--M5) using absorption line depths of Fe
I, OH, and Al I. The field star sample used here contains 254 K and M stars
with temperatures derived using BT-Settl synthetic spectra. We use 106 stars
with precise temperatures in the literature to calibrate our method with
typical errors of about 140 K, and systematic uncertainties less than 120
K. For the broadest applicability, we present T--line-depth-ratio
relationships, which we test on 12 members of the TW Hydrae Association and at
spectral resolving powers between 10,000--120,000. These ratios offer a
simple but accurate measure of effective temperature in cool stars that is
distance and reddening independent.Comment: 19 pages, 11 figures and 3 tables. Accepted in Ap
An Unexpected Discovery in the Rich Open Cluster NGC 6819 Using XMM-Newton
We present the first study of the X-ray population of the intermediate-age
rich open cluster NGC 6819 using the XMM-Newton Observatory. In the past
decade, Chandra X-ray observations have shown a relationship between the X-ray
population of globular clusters and their internal dynamics and encounter
frequency. We investigate the role dynamics possibly play in the formation of
X-ray sources in NGC 6819, and compare our results with known properties of
field and globular cluster X-ray populations. We implement a multi wavelength
approach to studying the X-ray sources, utilizing X-ray and UV data from XMM
observations along with the wealth of photometry and radial-velocity data from
the WIYN Open Cluster Study (WOCS) and the CFHT Open Cluster Survey. Within the
cluster half-light radius we detect 12 X-ray sources down to a luminosity of
10^30 erg/s for cluster members. The sources include a candidate quiescent
low-mass X-ray binary (qLMXB), a candidate cataclysmic variable, and two active
binary systems. The presence of a qLMXB in an open cluster is previously
unexpected given the known relationships between luminous X-ray sources and
encounter frequency in globular clusters, and most likely has a dynamical
origin.Comment: 14 pages, 11 figures, accepted for publication in the Astrophysical
Journa
Wolf 1130: A Nearby Triple System Containing a Cool, Ultramassive White Dwarf
Following the discovery of the T8 subdwarf WISE J200520.38+542433.9 (Wolf 1130C), which has a proper motion in common with a binary (Wolf 1130AB) consisting of an M subdwarf and a white dwarf, we set out to learn more about the old binary in the system. We find that the A and B components of Wolf 1130 are tidally locked, which is revealed by the coherence of more than a year of V-band photometry phase-folded to the derived orbital period of 0.4967 days. Forty new high-resolution, near-infrared spectra obtained with the Immersion Grating Infrared Spectrometer provide radial velocities and a projected rotational velocity (v sin i) of 14.7 ± 0.7 km s^(-1) for the M subdwarf. In tandem with a Gaia parallax-derived radius and verified tidal locking, we calculate an inclination of i = 29° ± 2°. From the single-lined orbital solution and the inclination we derive an absolute mass for the unseen primary (1.24^(+0.19)_(-0.15) M ⊙). Its non-detection between 0.2 and 2.5 μm implies that it is an old (>3.7 Gyr) and cool (T_(eff) 100 times the tertiary mass and the survival of the system through the common-envelope phase, where ~80% of the system mass was lost, is remarkable. Our analysis of Wolf 1130 allows us to infer its formation and evolutionary history, which has unique implications for understanding low-mass star and brown dwarf formation around intermediate-mass stars
Machine learning uncovers the most robust self-report predictors of relationship quality across 43 longitudinal couples studies
Given the powerful implications of relationship quality for health and well-being, a central mission of relationship science is explaining why some romantic relationships thrive more than others. This large-scale project used machine learning (i.e., Random Forests) to 1) quantify the extent to which relationship quality is predictable and 2) identify which constructs reliably predict relationship quality. Across 43 dyadic longitudinal datasets from 29 laboratories, the top relationship-specific predictors of relationship quality were perceived-partner commitment, appreciation, sexual satisfaction, perceived-partner satisfaction, and conflict. The top individual-difference predictors were life satisfaction, negative affect, depression, attachment avoidance, and attachment anxiety. Overall, relationship-specific variables predicted up to 45% of variance at baseline, and up to 18% of variance at the end of each study. Individual differences also performed well (21% and 12%, respectively). Actor-reported variables (i.e., own relationship-specific and individual-difference variables) predicted two to four times more variance than partner-reported variables (i.e., the partner’s ratings on those variables). Importantly, individual differences and partner reports had no predictive effects beyond actor-reported relationship-specific variables alone. These findings imply that the sum of all individual differences and partner experiences exert their influence on relationship quality via a person’s own relationship-specific experiences, and effects due to moderation by individual differences and moderation by partner-reports may be quite small. Finally, relationship-quality change (i.e., increases or decreases in relationship quality over the course of a study) was largely unpredictable from any combination of self-report variables. This collective effort should guide future models of relationships