ABSTRACT We present the results of a near-infrared (NIR) spectroscopic follow-up survey of 182 M4-L7 low-mass stars and brown dwarfs (BDs) from the BANYAN All-Sky Survey (BASS) for candidate members ...of nearby, young moving groups (YMGs). We confirm signs of low gravity for 42 new BD discoveries with estimated masses between 8 and 75 and identify previously unrecognized signs of low gravity for 24 known BDs. We refine the fraction of low-gravity dwarfs in the high-probability BASS sample to ∼82%. We use this unique sample of 66 young BDs, supplemented with 22 young BDs from the literature, to construct new empirical NIR absolute magnitude and color sequences for low-gravity BDs. We show that low-resolution NIR spectroscopy alone cannot differentiate between the ages of YMGs younger than ∼120 Myr, and that the BT-Settl atmosphere models do not reproduce well the dust clouds in field or low-gravity L-type dwarfs. We obtain a spectroscopic confirmation of low gravity for 2MASS J14252798-3650229, which is a new ∼27 , L4 γ bona fide member of AB Doradus. We identify a total of 19 new low-gravity candidate members of YMGs with estimated masses below 13 , 7 of which have kinematically estimated distances within 40 pc. These objects will be valuable benchmarks for a detailed atmospheric characterization of planetary-mass objects with the next generation of instruments. We find 16 strong candidate members of the Tucana-Horologium association with estimated masses between 12.5 and 14 , a regime where our study was particularly sensitive. This would indicate that for this association there is at least one isolated object in this mass range for every main-sequence stellar member, a number significantly higher than expected based on standard log-normal initial mass function, however, in the absence of radial velocity and parallax measurements for all of them, it is likely that this over-density is caused by a number of young interlopers from other associations.
Abstract
We present an analysis of the newly identified
μ
Tau Association (MUTA) of young stars at ≃150 pc from the Sun that is part of the large Cas-Tau structure, coeval and comoving with the
α
... Persei cluster. This association is also located in the vicinity of the Taurus-Auriga star-forming region and the Pleiades association, although it is unrelated to them. We identify more than 500 candidate members of MUTA using Gaia DR2 data and the BANYAN Σ tool, and we determine an age of 62 ± 7 Myr for its population based on an empirical comparison of its color–magnitude diagram sequence with those of other nearby young associations. The MUTA association is related to the Theia 160 group of Kounkel & Covey and corresponds to the e Tau group of Liu et al. It is also part of the Cas-Tau group of Blaauw. As part of this analysis, we introduce an iterative method based on spectral templates to perform an accurate correction of interstellar extinction of Gaia DR2 photometry, needed because of its wide photometric bandpasses. We show that the members of MUTA display an expected increased rate of stellar activity and faster rotation rates compared with older stars, and that literature measurements of the lithium equivalent width of nine G0- to K3-type members are consistent with our age determination. We show that the present-day mass function of MUTA is consistent with other known nearby young associations. We identify WD 0340+103 as a hot, massive white dwarf remnant of a B2 member that left its planetary nebula phase only 270,000 yr ago, posing an independent age constraint of
Myr for MUTA, consistent with our isochrone age. This relatively large collection of comoving young stars near the Sun indicates that more work is required to unveil the full kinematic structure of the complex of young stars surrounding
α
Persei and Cas-Tau.
Abstract
We present three new brown dwarf spectral-binary candidates: CWISE J072708.09−360729.2, CWISE J103604.84−514424.4, and CWISE J134446.62−732053.9, discovered by citizen scientists through the ...Backyard Worlds: Planet 9 project. Follow-up near-infrared spectroscopy shows that each of these objects is poorly fit by a single near-infrared standard. We constructed binary templates and found significantly better fits, with component types of L7+T4 for CWISE J072708.09−360729.2, L7+T4 for CWISE J103604.84−514424.4, and L7+T7 for CWISE J134446.62−732053.9. However, further investigation of available spectroscopic indices for evidence of binarity and large amplitude variability suggests that CWISE J072708.09−360729.2 may instead be a strong variability candidate. Our analysis offers tentative evidence and characterization of these peculiar brown dwarf sources, emphasizing their value as promising targets for future high-resolution imaging or photometric variability studies.
Introduction
Perinatal depression is common among women living with HIV, but depression care is limited in low-resource settings. We examined (1) characteristics of women receiving Problem Solving ...Therapy (PST) versus antidepressant therapy (ADT), (2) treatment response by modality, and (3) correlates of treatment response.
Methods
This analysis used data from 191 Ugandan women in the intervention arm of a cluster randomized controlled trial of task-shifted, stepped-care depression treatment for pregnant women living with HIV (PWLWH). Treatment response was defined as scoring < 5 on the nine-item Patient Health Questionnaire (PHQ-9). Bivariate analysis and multivariable logistic regression were used to examine characteristics of women by treatment group and correlates of treatment response.
Results
Of 134 participants with depression, 129 (96%) were treated: 84 (65%) received PST and 45 (35%) received ADT. Severe depression at treatment initiation was more common in those receiving ADT (28.9% versus 4.8%, Fischer’s Exact Test < 0.001). Treatment response was higher for PST (70/84; 83.3%) than ADT (30/45; 66.7%; p = .03). ADT side effects were rare and minor; no infants had serious congenital defects. Of 22 participants (19%) who did not respond to treatment, only five received intensified management. Social support and interpersonal violence were associated with treatment response (adjusted odds ratio, aOR = 3.06, 95% CI = 1.08–8.66 and aOR = 0.64, 95% CI = 0.44–0.93).
Discussion
Both depression treatment modalities yielded high response rates in Ugandan PWLWH; ADT was well-tolerated. Our results highlight a need to build capacity to implement the stepped-care protocol for non-responders and screen for social support and interpersonal violence.
Significance
What is Already Known on this Subject?
Prior research has demonstrated the feasibility and effectiveness of delivering collaborative care for depression in low-resource settings including Uganda.
What this Study adds?
Both Problem-Solving Therapy and antidepressant therapy yielded high treatment response rates among pregnant women living with HIV in Uganda who met criteria for depression, and antidepressant therapy was well tolerated. This study highlights a need to build capacity to implement the task-shifted stepped-care protocol for women whose depression does not respond to initial treatment, and to screen for social support and interpersonal violence.
BACKGROUND:Opioid agonist therapy (OAT) is the standard of care for pregnant women with opioid use disorder (OUD). Medicaid coverage policies may strongly influence OAT use in this group.
...OBJECTIVE:To examine the association between Medicaid coverage of methadone maintenance and planned use of OAT in the publicly funded treatment system.
RESEARCH DESIGN:Retrospective cross-sectional analysis of treatment admissions in 30 states extracted from the Treatment Episode Data Set (2013 and 2014).
SUBJECTS:Medicaid-insured pregnant women with OUD (n=3354 treatment admissions).
MEASURES:The main outcome measure was planned use of OAT on admission. The main exposure was state Medicaid coverage of methadone maintenance. Using multivariable logistic regression models adjusting for sociodemographic, substance use, and treatment characteristics, we compared the probability of planned OAT use in states with Medicaid coverage of methadone maintenance versus states without coverage.
RESULTS:A total of 71% of pregnant women admitted to OUD treatment were 18–29 years old, 85% were white non-Hispanic, and 56% used heroin. Overall, 74% of admissions occurred in the 18 states with Medicaid coverage of methadone maintenance and 53% of admissions involved planned use of OAT. Compared with states without Medicaid coverage of methadone maintenance, admissions in states with coverage were significantly more likely to involve planned OAT use (adjusted difference32.9 percentage points, 95% confidence interval, 19.2–46.7).
CONCLUSIONS:Including methadone maintenance in the Medicaid benefit is essential to increasing OAT among pregnant women with OUD and should be considered a key policy strategy to enhance outcomes for mothers and newborns.
'Cataclysmic variables' are binary star systems in which one star of the pair is a white dwarf, and which often generate bright and energetic stellar outbursts. Classical novae are one type of ...outburst: when the white dwarf accretes enough matter from its companion, the resulting hydrogen-rich atmospheric envelope can host a runaway thermonuclear reaction that generates a rapid brightening. Achieving peak luminosities of up to one million times that of the Sun, all classical novae are recurrent, on timescales of months to millennia. During the century before and after an eruption, the 'novalike' binary systems that give rise to classical novae exhibit high rates of mass transfer to their white dwarfs. Another type of outburst is the dwarf nova: these occur in binaries that have stellar masses and periods indistinguishable from those of novalikes but much lower mass-transfer rates, when accretion-disk instabilities drop matter onto the white dwarfs. The co-existence at the same orbital period of novalike binaries and dwarf novae-which are identical but for their widely varying accretion rates-has been a longstanding puzzle. Here we report the recovery of the binary star underlying the classical nova eruption of 11 March AD 1437 (refs 12, 13), and independently confirm its age by proper-motion dating. We show that, almost 500 years after a classical-nova event, the system exhibited dwarf-nova eruptions. The three other oldest recovered classical novae display nova shells, but lack firm post-eruption ages, and are also dwarf novae at present. We conclude that many old novae become dwarf novae for part of the millennia between successive nova eruptions.
A determination of the initial mass function (IMF) of the current, incomplete census of the 10 Myr-old TW Hya association (TWA) is presented. This census is built from a literature compilation ...supplemented with new spectra and 17 new radial velocities from ongoing membership surveys, as well as a reanalysis of Hipparcos data that confirmed HR 4334 (A2 Vn) as a member. Although the dominant uncertainty in the IMF remains census incompleteness, a detailed statistical treatment is carried out to make the IMF determination independent of binning while accounting for small number statistics. The currently known high-likelihood members are fitted by a log-normal distribution with a central mass of M and a characteristic width of dex in the 12 MJup-2 M range, whereas a Salpeter power law with best describes the IMF slope in the 0.1-2 M range. This characteristic width is higher than other young associations, which may be due to incompleteness in the current census of low-mass TWA stars. A tentative overpopulation of isolated planetary-mass members similar to 2MASS J11472421-2040204 and 2MASS J11193254-1137466 is identified: this indicates that there might be as many as similar members of TWA with hot-start model-dependent masses estimated at ∼5-7 MJup, most of which would be too faint to be detected in 2MASS. Our new radial velocity measurements corroborate the membership of 2MASS J11472421-2040204, and secure TWA 28 (M8.5 γ), TWA 29 (M9.5 γ), and TWA 33 (M4.5 e) as members. The discovery of 2MASS J09553336-0208403, a young L7-type interloper unrelated to TWA, is also presented.
We have estimated fundamental parameters for a sample of co-moving stars observed by Gaia and identified by Oh et al. We matched the Gaia observations to the 2MASS and Wide-Field Infrared Survey ...Explorer catalogs and fit MIST isochrones to the data, deriving estimates of the mass, radius, Fe/H, age, distance, and extinction to 9754 stars in the original sample of 10606 stars. We verify these estimates by comparing our new results to previous analyses of nearby stars, examining fiducial cluster properties, and estimating the power-law slope of the local present-day mass function. A comparison to previous studies suggests that our mass estimates are robust, while metallicity and age estimates are increasingly uncertain. We use our calculated masses to examine the properties of binaries in the sample and show that separation of the pairs dominates the observed binding energies and expected lifetimes.
We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary ...systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical-mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color-color diagrams. We report new polynomial relations between spectral type and M sub(JHK). Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a "bright" (unresolved binary) and a "faint" (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0-T4 sources is prominent in M sub(J) where there is a 1.2-1.4 mag difference. A similar yet dampened brightening of 0.3-0.5 mag happens at M sub(H) and a plateau or dimming of -0.2 to -0.3 mag is seen in M sub(K). Comparison with evolutionary models that vary gravity, metallicity, and cloud thickness verifies that for L into T dwarfs, decreasing cloud thickness reproduces brown dwarf near-IR color-magnitude diagrams. However we find that a near constant temperature of 1200 + or -100 K along a narrow spectral subtype of T0-T4 is required to account for the brightening and color-magnitude diagram of the L-dwarf/T-dwarf transition. There is a significant population of both L and T dwarfs which are red or potentially "ultra-cloudy" compared to the models, many of which are known to be young indicating a correlation between enhanced photospheric dust and youth. For the low surface gravity or young companion L dwarfs we find that 8 out of 10 are at least 0.2-1.0mag underluminous in M sub(JH) and/or M sub(K) compared to equivalent spectral type objects. We speculate that this is a consequence of increased dust opacity and conclude that low surface gravity L dwarfs require a completely new spectral-type/absolute magnitude polynomial for analysis.
We report on nine wide common proper motion systems containing late-type M, L, or T companions. We confirm six previously reported companions, and identify three new systems. The ages of these ...systems are determined using diagnostics for both stellar primaries and low-mass secondaries and masses for the secondaries are inferred using evolutionary models. Of our three new discoveries, the M3+T6.5 pair G 204-39 and SDSS J1758+4633 has an age constrained to 0.5-1.5 Gyr making the secondary a potentially useful brown dwarf benchmark. The G5+L4 pair G 200-28 and SDSS J1416+5006 has a projected separation of ~25,000 AU making it one of the widest and lowest binding energy systems known to date. The system containing NLTT 2274 and SDSS J0041+1341 is an older M4+L0 (>4.5 Gyr) pair which shows H Delta *a activity in the secondary but not the primary making it a useful tracer of age/mass/activity trends. Two of the nine systems have discrepant component ages that emerge from stellar or ultracool diagnostics indicating possible shortcomings in our understanding of the age diagnostics of stars and brown dwarfs. We find a resolved binary frequency for widely separated (>100 AU) low-mass companions (i.e., at least a triple system) which is at least twice the frequency found for the field ultracool dwarf population. The ratio of triples to binaries and quadruples to binaries is also high for this sample: 3:5 and 1:4, respectively, compared to 8 pc sample values of 1:4 and 1:26. The additional components in these wide companion systems indicates a formation mechanism that requires a third or fourth component to maintain gravitational stability or facilitate the exchange of angular momentum. The binding energies for the nine multiples discussed in this text are among the lowest known for wide low-mass systems, suggesting that weakly bound, low-to-intermediate mass (0.2 M < M tot< 1.0 M ) multiples can form and survive to exist in the field (1-8 Gyr).
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