OB Population Research Articles

Status of reserves and fishing of peled Coregonus peled Middle Obi within the borders of the Tomsk region

The peled Coregonus peled is common in the water bodies of the Arctic. Peled reaches high numbers and biomass in the Ob-Irtysh basin coast of Eurasia. It lives in all major rivers of Siberia and it is a typical semi-anadromous species. It is assumed that in the Ob basin there are at least two subpopulations of peled, one of which reproduces in the Ural tributaries of the Ob (Lower Ob), the other in its middle reaches (Middle Ob). Peled in the Middle Ob within the boundaries of the Tomsk region is the main commercial target among whitefish species. Within the Tomsk region, fishing for the Middle Ob population of peled is carried out during its spawning migration, in September-October, on the approach to places of natural reproduction. In this study presents information about the stock, official catch and total allowable catches (TAC) of peled in the Middle Ob in the Tomsk region. In the last decade, the biomass of commercial peled stocks in the Middle Ob varies from 532.1 to 1349.7 tons, averaging 746.1 tons. According to official statistics, the catch of peled in the period from 2013 to 2022 ranged from 39.1 t to 89.7 t, which is below the TAC. According to calculated data, the actual volume of peled removal ranges from 19.9 tons to 86.7 tons or 27–118% of the legal catch of this species, which significantly exceeds the TAC. Thus, excessive fishing pressure on the spawning stock of peled will likely lead to a decrease in the reproductive capacity of the population and will have a negative impact on the state of peled stocks in the Ob basin as a whole.

The assessment of Kunovat sanctuary natural complexes in the area of the Siberian white crane (<i>Leucogeranus leucogeranus</i>) reintroduction

The paper deals with the research of soils, vegetation, bird and mammal population composition and structure in the vicinity of the white crane field research station in the Kunovat sanctuary (Kunovat Zakaznik), northern taiga subzone, Shuryshkarsky District, Yamalo-Nenets Autonomous Okrug, Russia. The aim of this investigation is to assess the present state of natural complexes in the area of the critically endangered Leucogeranus leucogeranus Ob population reintroduction. It has been established that various components of the natural complexes under study are generally consistent with the zone-and-province landscape, climate and biotope peculiarities of the area, which is a sign of their good health and relative stability. At the same time, in small mammal communities (an indicator group) the resistant sustainability index has been higher than the resilient sustainability index for two years in a row, which is characteristic of disturbed habitats or of early ecological succession stages. Such imbalance may be accounted for by local wild fires and floods in the natural complex under study. Botaurus stellaris nests have been registered in different parts of the quaking (white crane) bog, whose breeding grounds used to lie further to the south. This is evidence that the species range moves to the high latitudes and that the global climate change influences the natural complexes in the historic breeding area of the West-Siberian white crane population.

Stellar clustering and the kinematics of stars around Collinder 121 using Gaia DR3

ABSTRACT We study the region around Collinder 121 (Cr 121) using newly available 6D data from the Gaia DR3 catalogue. Situated in the third quadrant, near the Galactic plane, Collinder 121 lies in the region of Canis Major centred around (l, b) ≈(236°, −10°). Previous studies have suggested that the stellar associations in this region comprise an OB association (CMa OB2) lying at about 740 pc with a more distant open cluster (Cr 121) at approximately 1170 pc. Despite these studies, the precise nature of Collinder 121 remains uncertain. This study investigates the region bounded by the box (l, b) = (225°–245°, 0.00° to −20.00°) to a depth of 700 pc from 500 to 1200 pc which fully encompasses the region discussed in the literature. Using Gaia DR3 data, we do not find associations at the distances given in the literature. Instead, using the hdbscan machine learning algorithm, we find a major association of OB stars centred around 803 pc. Within this association we find four smaller subgroups that may be indicative of a larger association and which are located at a mean distance of 827 pc. Proper motion studies find coherence between these four subgroups and show a distinctive east-to-west increase in the size of the velocity vectors which supports contemporary studies that show similar trends in OB populations in Cygnus and within the Carina spiral Arm. Therefore, we hypothesize that Cr 121 and CMa OB2 are the same cluster, consistent with the 1977 study by Hoogerwerf.

Implementation of genetic carrier screening in the OB population: guideline recommendation adherence

Implementation of genetic carrier screening in the OB population: guideline recommendation adherence

A VLT/FLAMES survey for massive binaries in Westerlund 1

Context. The galactic cluster Westerlund 1 contains a rich population of evolved, massive stars. A high binary fraction has been inferred from previous multi-wavelength observations. Aims. We use multi-epoch spectroscopy of a large sample of early-type stars in Westerlund 1 to identify new binaries and binary candidates in the cluster. Methods. VLT/FLAMES was used with the GIRAFFE spectrograph in HR21 mode to obtain spectra of ∼100 OB stars over a 14-month baseline in 2008 and 2009, supplemented with follow-up observations in 2011 and 2013. Radial velocities were obtained from strong Paschen series absorption lines in the I-band. Results. We identify 20 new OB I–III binaries, a WN9h binary, and a WC9d binary, greatly increasing the number of directly confirmed binary systems in Westerlund 1, while 12 O9−9.5 Iab−III stars are identified as candidate binaries based on radial velocity changes that are inconsistent with photospheric variability. The 173.9 day SB1 W1030 represents the first longer-period system identified in the cluster, while the determination of a 53.95 day period for W44 (WR L) makes it the first Wolf-Rayet binary in Westerlund 1 with a confirmed orbital period greater than ten days. Our results suggest the binary fraction in the OB population is at least ∼40%, and may be significantly higher. Conclusions. These results demonstrate that binary systems can be effectively identified in the population of OB I−III stars evolving off the main sequence in Westerlund 1. Future multi-epoch surveys will be able to fully characterise this population.

Experience of using dry biomass of methanotrophic bacteria in the enrichment of artificial feeds for Siberian sturgeon juveniles of the Ob population

The article discusses the results of a study on the enrichment of artificial feeds with dry biomass of methanotrophic bacteria of 10 and 20% concentration and fatty acids (treatment “Arfit”, linseed oil). The data on the increase in body length and weight, the survival rate of Siberian sturgeon juveniles, depending on the applied preparations introduced, are presented. The best results were obtained when 10% of dry biomass of methanotrophic bacteria and HUFA were added to the feed (acceleration of weight growth by 44%, linear growth by 38%). The presented results are aimed at developing some elements of the technology for enriching artificial feeds with microbiosynthesis products.

Определение эффективности работ по искусственному воспроизводству пеляди Coregonus peled в Обь-Иртышском бассейне

The method of determining the effectiveness of artificial reproduction works is considered on the example of the Ob population of peled. The method is based on recording the moment when the population decline stops, and the subsequent increase in catches. Based on the average fishing return rate of 0.258% of the 1.5 g young, the catch from one million young is about 0.8 tons. It is established that the catch can increase to 2.6 tons per one million juveniles after the entry into the fishery of new offspring from the replenishment of the spawning herd. Taking into account the mass onset of sexual maturity of the peled at the 4th year of life, the greatest effect of artificial reproduction is observed at the 8th year. The equations for determining the period and level of restoration of the bioresource are given. It is noted that for the restoration of long-cycle fish species, the volume of young fish introduction should be at least 20 % of the receiving capacity. The rate of recovery of the bioresource depends on the following indicators: the volume of the introduction of juveniles, the intensity of fishing, the age of sexual maturity and the availability of conditions for natural reproduction.

Abstract 2036: Osteoblasts use multiple mechanisms of cellular communication to regulate breast cancer cell proliferation in bone

Abstract Breast cancer (BC) preferentially metastasizes to bone. While the mechanism for preferred metastasis is unknown, bone likely provides a hospitable environment that attracts BC cells (BCCs) and allows them to colonize and grow. Bone metastases perturb the balance of normal bone remodeling. Emerging evidence suggests that OBs may be altered and respond differently to cancer cells during metastatic BC progression. According to one study, OBs suppress cancer cell growth in early metastasis. Our work suggests OBs reduce BCC growth in bone prior to macrometastatic colonization. Thus, our data suggest OBs have tumor-inhibitory properties. We have new evidence to suggest that communication between OBs and BCCs ‘educates’ OBs to produce factors that suppress BCC proliferation in bone. We have in-vitro and in-vivo mouse-model evidence that ‘educated’ osteoblasts (EOs) have a unique secretory protein profile compared to ‘uneducated’ OBs. We also identified EOs as being present in the bone tissue samples of human patients with bone metastatic BC via multi-plex immunofluorescence. When we treated BCCs with EO conditioned media (CM), BCC proliferation was reduced in both triple negative and ER+ metastatic BCCs, while CM from ‘uneducated’ OBs did not affect BCC proliferation. This effect was mediated through alterations in EO production of decorin and NOV. We identified EO CM as a rich source of exosomes (exo) and confirmed the presence of an exo population via iodixanol density gradient and western blotting for specific exo protein markers. We found that EO-derived exo, but not ‘uneducated’ OB-derived exo, decreased proliferation of ER+ and triple negative BCC. Also, exposure to EO-derived exo 1) decreased the number of Ki67 positive metastatic BCC, and 2) decreased the number of metastatic BCC in the S phase of cell cycle as measured by EdU incorporation. Moreover, we labeled EO exo with RFP-conjugated CD63 to visually confirm exo transfer from EO cells to BCCs using confocal microscopy. And, co-culture with EOs increased triple negative and ER+ metastatic BC expression of p21 compared to co-cultures with ‘uneducated’ OBs. Our data suggest that EOs use multiple mechanisms of cellular communication to regulate BCC proliferation in bone. Impact: Our data suggest OBs produce factors that suppress metastatic BCC growth. Much less attention has been given to OB interactions with tumor cells at sites of bone metastasis due to observations that OB populations are reduced at sites of advanced osteolysis. However, we propose that OBs may be valuable endogenous targets to aid in suppression of metastatic BC growth in the niche in concert with therapeutic drugs to kill the cancer cells. Our data suggest there is a population of OBs that demonstrate a functional role in suppressing metastatic BCC growth; a property capable of exploitation. For these reasons, OBs and EOs are strong candidates for therapeutic targeting. Citation Format: Alexus D. Kolb, Alison B. Shupp, Dimpi Mukhopdhyay, Karen M. Bussard. Osteoblasts use multiple mechanisms of cellular communication to regulate breast cancer cell proliferation in bone [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2036.

SAT-LB045 Maternal Obesity in Early Pregnancy Is Associated with the Decreased Active IGF-I Availability and Increased Leptin Concentrations

Introduction: Maternal obesity (MO) is the global health problem, associated with high fetal and maternal mortality. Cardiovascular remodelling in obese pregnant patients has been linked to development of preeclampsia. IGF-I is important for maternal adaptation to pregnancy, e.g. maternal tissue growth and metabolism. Pregnancy-associated plasma protein-A2 (PAPP-A2) is a metalloproteinase that specifically cleaves IGFBP-3 and IGFBP-5 releasing active IGF-I. Leptin, produced by placenta and adipose tissue, is a cytokine with cardio metabolic properties, the concentration of which is increased in obese subjects and in pregnant patients. The aim of this study was to evaluate serum levels of PAPP-A2 (as an indicator of IGF -I pathway activation) and Leptin in the obese and non-obese patients in first trimester of pregnancy. Glycosylated fibronectin (GlyFib) and Inhibin A (Inh A) were evaluated as additional a markers of remodelling and placental function (respectively). Material and methods. This was a prospective observational study, patients were enrolled during first trimester of pregnancy according to the IRB-approved protocol (L#17-136): obese (OB, BMI ≥ 30 kg/m2, n=13) and non-obese (nOB, BMI<30 kg/m2 , n=14). Patients with pre-pregnancy cardiovascular pathology were excluded. Concentrations of PAAP-A2, GlyFib, Inh A and Leptin were measured, using commercially available ELISAs: AL-109, AL-123 and AL-160 from AnshLab (Webster, TX, USA) and Invitrogen (Waltham, MA). The data are presented as Mean ± SEM. Results. In 3/13 OB and in 1/14 nOB patients PAAP-A2 concentrations were below 0.3 MoM (CI [4.8 - 34 ng/ml] and [CI 5.8-21 ng/ml] respectively). GlyFib (OB, 303.4 ± 35.6 µg/ml; nOB, 208.7 ± 19.26 µg/ml) and Leptin concentrations (OB, 72775 ± 3802 pg/ml; nOB, 48882 ± 4052 pg/ml) were increased in OB patients compared to nOB (*p<0.05; ***p<0.0005, Mann-Whitney test, respectively). Inh A concentrations (OB, 479.6 ± 105.9 pg/ml; nOB, 381 ± 81.65 pg/ml) did not differ between two groups. In the nOB population, incidence of preeclampsia was 1/15 (6.7%) which was not associated with low PAPP-A2 levels. In the OB population, incidence of preeclampsia was 3/10 (30%) where 2/3 of cases were associated with low PAPP-A2 levels. Discussion. IGF-I and Leptin regulate cardiovascular remodelling and placentation. The mismatch of these two factors might represent the mechanism of pathological cardiovascular adaptation in OB pregnant patients. Limitations of this study are small sample size, non-inclusion of other predisposed populations (PCOS, GDM, autoimmune disorders) and loss to follow-up. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. s presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

The low-mass population of the Vela OB2 association from Gaia

ABSTRACT The first Gaia Data Release presents an opportunity to characterize the low-mass population of OB associations, providing larger statistical samples and better constraints on the formation and evolution of clusters and associations. Using previously known low-mass members in a small region of Vela OB2, we have designed selection criteria that combine Gaia and 2MASS photometry, independently of any astrometric information, to identify low-mass pre-main-sequence stars over the wider association area. Our method picks out the known clusters of young stars around γ2 Velorum and NGC-2547, but also identifies other overdensities that may represent previously unknown clusters. There are clear differences in the spatial distributions of the low-mass and the high-mass OB populations, suggesting either that the structure and dynamics of these populations has evolved separately or that the initial mass function can vary considerably on small scales within a single association.

High Resolution Optical Spectroscopy of an Intriguing High-Latitude B-Type Star HD119608

We present an LTE analysis of high resolution echelle optical spectra obtained with the 3.9-m Anglo-Australian Telescope (AAT) and the UCLES spectrograph for a B1Ib high galactic latitude supergiant HD119608. A fresh determination of the atmospheric parameters using line-blanketed LTE model atmospheres and spectral synthesis provided Teff = 23 300 ± 1000 K, log g = 3.0 ± 0.3, and the microturbulent velocity ξ = 6.0 ± 1.0 kms−1 and [Fe/H] = 0.16. The rotational velocity of the star was derived fromC, O, N, Al, and Fe lines as v sin i = 55.8 ± 1.3 kms−1. Elemental abundances were obtained for 10 different species. He, Al, and P abundances of the star were determined for the first time. In the spectra, hot post-AGB status as well as the Pop I characteristics of the star were examined. The approximately solar carbon and oxygen abundances, along with mild excess in helium and nitrogen abundances do not stipulate a CNO processed surface composition, hence a hot post-AGB status. The LTE abundances analysis also indicates solar sulphur and moderately enriched magnesium abundances. The average abundances of B dwarfs of well studied OB associations and Population I stars show a striking resemblance to abundances obtained for HD119608 in this study. This may imply a runaway status for the star.

СТАТУС СИГА-ПЫЖЬЯНА COREGONUS LAVARETUS PIDSCHIAN (GMELIN, 1788) В СИСТЕМЕ РЕКА ТАНЬЮ - ОЗЕРО ВАРЧАТО (БАССЕЙН РЕКИ ВОЙКАР)

The Voikar river is a spawning tributary of the lower Ob. Spawning grounds of Siberian whitefish are located both on the river Voikar and on the river Tanju (a tributary of the Voikar), which flows into lake Varchato. The Varchatovis canal flows out of lake Varchato and merges with the river Voikar. Studies have shown that in the system the Tanju river - lake Varchato live Siberian whitefish different from those of other Ural spawning tributaries of the Ob river and of the Ob itself by their age structure, presence of only re-maturing species with a high rate of growth and fecundity. It was found that after breeding on the spawning ground in the Tanju river some individuals of Siberian whitefish do not flow to the Ob river, but remain in system the Tanju river - Varchato lake. In two or three years it matures and goes back to spawn in the Tanju river, merging with the spawning stock which goes up the Ob river. There are no individuals that are constantly living in lake Varchato, as all juveniles, when still being larvae, flow down to the Ob river. That gives grounds for including Siberian whitefish of Varchato lake into the Ob population of semi-passing Siberian whitefish. The presence of re-maturing species in the system of the Tanju river - lake Varchato creates reproductive reserve of breeders that increase heterogeneity and population size. However, in the last decade as a result of total poaching of Siberian whitefish in lake Varchato during feeding and wintering its numbers declined sharply.

Candidate X-Ray-emitting OB Stars in MYStIX Massive Star-forming Regions

Abstract Massive O-type and early B-type (OB) stars in the nearby Galaxy remain incompletely cataloged due to high extinction, bright visible and infrared nebular emission in H ii regions, and high field star contamination. These difficulties are alleviated by restricting the search to stars with X-ray emission. Using the X-ray point sources from the Massive Young Star-forming Complex Study in Infrared and X-Rays (MYStIX) survey of OB-dominated regions, we identify 98 MYStIX candidate OB (MOBc) stars by fitting their 1–8 μm spectral energy distributions (SEDs) with reddened stellar atmosphere models. We identify 27 additional MOBc stars based on JHK S photometry of X-ray stars lacking SED fitting. These candidate OB stars indicate that the current census of stars earlier than B1, taken across the 18 MYStIX regions studied, is less than 50% complete. We also fit the SEDs of 239 previously published OB stars to measure interstellar extinction and bolometric luminosities, revealing six candidate massive binary systems and five candidate O-type (super)giants. As expected, candidate OB stars have systematically higher extinction than previously published OB stars. Notable results for individual regions include identification of the OB population of a recently discovered massive cluster in NGC 6357, an older OB association in the M17 complex, and new massive luminous O stars near the Trifid Nebula. In several relatively poorly studied regions (RCW 38, NGC 6334, NGC 6357, Trifid, and NGC 3576), the OB populations may increase by factors of .

Художественная реконструкция женского костюма населения Верхнего Приобья эпохи раннего железа

Художественная реконструкция женского костюма населения Верхнего Приобья эпохи раннего железа

A HIGH-RESOLUTION MULTIBAND SURVEY OF WESTERLUND 2 WITH THE HUBBLE SPACE TELESCOPE. II. MASS ACCRETION IN THE PRE-MAIN-SEQUENCE POPULATION

ABSTRACT We present a detailed analysis of the pre-main-sequence (PMS) population of the young star cluster Westerlund 2 (Wd2), the central ionizing cluster of the H ii region RCW 49, using data from a high-resolution multiband survey with the Hubble Space Telescope. The data were acquired with the Advanced Camera for Surveys in the F555W, F814W, and F658N filters and with the Wide Field Camera 3 in the F125W, F160W, and F128N filters. We find a mean age of the region of 1.04 ± 0.72 Myr. The combination of dereddened F555W and F814W photometry in combination with F658N photometry allows us to study and identify stars with Hα excess emission. With a careful selection of 240 bona-fide PMS Hα excess emitters we were able to determine their Hα luminosity, which has a mean value . Using the PARSEC 1.2S isochrones to obtain the stellar parameters of the PMS stars, we determined a mean mass accretion rate per star. A careful analysis of the spatial dependence of the mass accretion rate suggests that this rate is ∼25% lower in the center of the two density peaks of Wd2 in close proximity to the luminous OB stars, compared to the Wd2 average. This rate is higher with increasing distance from the OB stars, indicating that the PMS accretion disks are being rapidly destroyed by the far-ultraviolet radiation emitted by the OB population.

OPTICAL SPECTROSCOPY OF X-RAY-SELECTED YOUNG STARS IN THE CARINA NEBULA

We present low-resolution optical spectra for 29 X-ray sources identified as either massive star candidates or low-mass pre-main-sequence (PMS) star candidates in the clusters Trumpler 16 and Trumpler 14 of the Carina Nebula. Spectra of two more objects (one with an X-ray counterpart, and one with no X-ray counterpart), not originally our targets, but found close (~3'') to two of our targets, are presented as well. Twenty early-type stars, including an O8 star, seven B1–B2 stars, two B3 stars, a B5 star, and nine emission-line stars, are identified. Eleven T Tauri stars, including eight classical T Tauri stars (CTTSs) and three weak-lined T Tauri stars, are identified. The early-type stars in our sample are more reddened compared to the previously known OB stars of the region. The Chandra hardness ratios of our T Tauri stars are found to be consistent with the Chandra hardness ratios of T Tauri stars of the Orion Nebula Cluster. Most early-type stars are found to be nonvariable in X-ray emission, except the B2 star J104518.81–594217.9, the B3 star J104507.84–594134.0, and the Ae star J104424.76–594555.0, which are possible X-ray variables. J104452.20–594155.1, a CTTS, is among the brightest and the hardest X-ray sources in our sample, appears to be a variable, and shows a strong X-ray flare. The mean optical and near-infrared photometric variability in the V and Ks bands, of all sources, is found to be ~0.04 and 0.05 mag, respectively. The T Tauri stars show significantly larger mean variation, ~0.1 mag, in the Ks band. The addition of one O star and seven B1–B2 stars reported here contributes to an 11% increase of the known OB population in the observed field. The 11 T Tauri stars are the first ever confirmed low-mass PMS stars in the Carina Nebula region.

Differential temporal effects of sclerostin antibody and parathyroid hormone on cancellous and cortical bone and quantitative differences in effects on the osteoblast lineage in young intact rats

Sclerostin antibody (Scl-Ab) and parathyroid hormone (PTH) are bone-forming agents that have different modes of action on bone, although a study directly comparing their effects has not been conducted. The present study investigated the comparative quantitative effects of these two bone-forming agents over time on bone at the organ, tissue, and cellular level; specifically, at the level of the osteoblast (Ob) lineage in adolescent male and female rats. Briefly, eight-week old male and female Sprague–Dawley rats were administered either vehicle, Scl-Ab (3 or 50mg/kg/week subcutaneously), or human PTH (1–34) (75μg/kg/day subcutaneously) for 4 or 26weeks. The 50mg/kg Scl-Ab and the PTH dose were those used in the respective rat lifetime pharmacology studies. Using robust stereological methods, we compared the effects of these agents specifically at the level of the Ob lineage in vertebrae from female rats. Using RUNX2 or nestin immunostaining, location, and morphology, the total number of osteoprogenitor subpopulations, Ob, and lining cells were estimated using the fractionator or proportionator estimators. Density estimates were also calculated referent to total bone surface, total Ob surface, or total marrow volume.Scl-Ab generally effected greater increases in cancellous and cortical bone mass than PTH, correlating with higher bone formation rates (BFR) at 4weeks in the spine and mid-femur without corresponding increases in bone resorption indices. The increases in vertebral BFR/BS at 4weeks attenuated with continued treatment to a greater extent with Scl-Ab than with PTH. At 4weeks, both Scl-Ab and PTH effected equivalent increases in total Ob number (Ob.N). Ob density on the formative surfaces (Ob.N/Ob.S) remained similar across groups while mineral apposition rate (MAR) was significantly higher with Scl-Ab at week 4, reflecting an increase in individual Ob vigor relative to vehicle and PTH. After 26weeks, Scl-Ab maintained BFR/BS with fewer Ob and lower Ob.N/Ob.S by increasing the Ob footprint (bone surface area occupied by an Ob) and increasing MAR, compared with PTH. The lower Ob.N and Ob.N/Ob.S with Scl-Ab at 26weeks were associated with decreased osteoprogenitor numbers compared with both vehicle and PTH, an effect not evident at week 4. Osteoprogenitor numbers were generally positively correlated with Ob.N across groups and timepoints, suggesting dynamic coordination between the progenitor and Ob populations. The time-dependent reductions in subpopulations of the Ob lineage with Scl-Ab may be integral to the greater attenuation or self-regulation of bone formation observed at the vertebra, as PTH required more Ob at the formative site with correlative increased numbers of progenitors compared with Scl-Ab indicating potentially greater stimulus for progenitor pool proliferation or differentiation.

Infrared properties of active OB stars in the Magellanic Clouds from the Spitzer SAGE survey

AbstractWe present a study of the infrared properties of 4922 spectroscopically confirmed massive stars in the Large and Small Magellanic Clouds, focusing on the active OB star population. Besides OB stars, our sample includes yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the red, and find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We also find photometric variability among the active OB population and evidence for transitions of Be stars to B stars and vice versa. We furthermore confirm the presence of dust around all the supergiant B[e] stars in our sample, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs.

The Fraction of Runaway OB Stars in the SMC Field

AbstractThe fraction of field OB stars that originate from clusters can help probe the dynamical evolution of clusters. Field stars represent a significant fraction (20-30%) of the OB population in galaxies, and estimates for the fraction of field OB stars that are runaways range from the classical value of &lt;10% (Blaauw 1961) to contemporary results suggesting &gt;90% (de Wit et al. 2005). We obtained Magellan IMACS observations on the kinematics of field OB stars in the SMC to examine the line-of-sight velocities of this population. Using these observations, we will estimate the fraction of runaways to serve as a probe of cluster evolution.

The Hard X‐Ray Luminosity of OB Star Populations: Implications for The Contribution of Star Formation to the Cosmic X‐Ray Background

We present an empirical analysis of the integrated X-ray luminosity arising from populations of OB stars. In particular, we utilize results from the All-Sky Monitor on RXTE, along with archival data from previous missions, to assess the mean integrated output of X-rays in the 2-10 keV band from accreting early-type binaries within 3 kpc of the Sun. Using a recent OB star census of the solar neighborhood, we then calculate the specific X-ray luminosity per O star from accretion-powered systems. We also assess the contribution to the total X-ray luminosity of an OB population from associated T Tauri stars, stellar winds, and supernovae. We repeat this exercise for the major Local Group galaxies, concluding that the total X-ray luminosity per O star spans a broad range from 2 to 20 × 1034 ergs s-1. Contrary to previous results, we do not find a consistent trend with metallicity; in fact, the specific luminosities for M31 and the SMC are equal, despite having metallicities that differ by an order of magnitude. In light of these results, we assess the fraction of the observed 2-10 keV emission from starburst galaxies that arises directly from their OB star populations, concluding that, while binaries can explain most of the hard X-ray emission in many local starbursts, a significant additional component or components must be present in some systems. A discussion of the nature of this additional emission, along with its implications for the contribution of starbursts to the cosmic X-ray background, concludes our report.