Search

LMCe055-1 was recently discovered in a survey for WRs in the Large Magellanic Cloud, and classified as a WN4/O4, a lower excitation version of the WN3/O3 class discovered as part of the same survey. Its absolute magnitude precluded it from being a WN4+O4 binary. OGLE photometry show shallow primary and secondary eclipses with a 2.2 day period. The spectral characteristics and short period pointed to a possible origin due to binary stripping. Such stripped WR binaries should be common but have proven elusive to identify conclusively. In order to establish its nature, we obtained HST UV and Magellan optical spectra, along with imaging. Our work shows that the WR emission and He II absorption arise in one star, and the He I absorption in another. The He I contributor is the primary of the 2.2-day system and exhibits ~300 km/sed radial velocity variations on that time scale. However, the WR star shows 30-40 km/sed radial velocity variations, with a likely 35-day period and a highly eccentric orbit. Possibly LMCe055-1 is a physical triple, but that would require the 2.2-day pair to have been captured by the WR star. A more likely explanation is that the WR star has an unseen companion in a 35-day orbit and that the 2.2-day pair is in a longer period orbit about the two. Such examples of multiple systems are well known among massive stars, such as HD 5980. Regardless, we argue that it is highly unlikely that the WR component of the LMCe055-1 system resulted from stripping., Comment: Accepted for publication in the Astrophysical Journal

Wolf-Rayet stars (WRs) are evolved massive stars in the brief stage before they undergo core collapse. Not only are they rare, but they also can be particularly difficult to find due to the high extinction in the Galactic plane. This paper discusses the discovery of three new Galactic WRs previously classified as H$\alpha$ emission stars, but thanks to Gaia spectra, we were able to identify the broad, strong emission lines that characterize WRs. Using the Lowell Discovery Telescope and the DeVeny spectrograph, we obtained spectra for each star. Two are WC9s, and the third is a WN6 + O6.5 V binary. The latter is a known eclipsing system with a 4.4 day period from ASAS-SN data. We calculate absolute visual magnitudes for all three stars to be between -7 and -6, which is consistent with our expectations of these subtypes. These discoveries highlight the incompleteness of the WR census in our local volume of the Milky Way and suggest the potential for future Galactic WR discoveries from Gaia low-dispersion spectra. Furthermore, radial velocity studies of the newly found binary will provide direct mass estimates and orbital parameters, adding to our knowledge of the role that binarity plays in massive star evolution., Comment: Accepted for publication in the Astronomical Journal

We observed the Galactic open cluster Berkeley 50 in order to determine its stellar content, distance, and age. We obtained UBV photometry of 1145 stars in a 12.3' $\times$ 12.3' field, and used Gaia proper motions and parallaxes to identify 64 members, of which we obtained spectra of the 17 brightest members. The majority of the observed population we classified as B dwarfs, with the exception of a newly identified red supergiant star, which our spectroscopy shows has a B-type companion. Our study establishes the distance as 3.8 kpc, with an average color-excess $E(B-V)=0.9$. Comparison of the physical properties of the cluster with the Geneva evolutionary tracks places the age of the cluster as 50-60 Myr, with its most massive members being $\sim7M_\odot$., Comment: Astronomical Journal, in press. This revision contains additional acknowledgements

The evolved massive star populations of the Local Group galaxies are generally thought to be well-understood. However, recent work suggested that the Wolf-Rayet (WR) content of M31 may have been underestimated. We therefore began a pilot project to search for new WRs in M31 and re-examine the completeness of our previous WR survey finished almost a decade prior. Our improved imaging data and spectroscopic follow-up confirmed 19 new WRs across three small fields in M31. These newly discovered WRs are generally fainter than the previously known sample due to slightly increased reddening as opposed to intrinsic faintness. From these findings, we estimate that there are another ~60 WRs left to be discovered in M31; however, the overall ratio of WN-type (nitrogen-rich) to WC-type (carbon-rich) WRs remains unchanged with our latest additions to the M31 WR census. We are in the process of extending this pilot WR survey to include the rest of M31, and a more complete population will be detailed in our future work., Comment: accepted in AJ. Updated acknowledgements

The WN3/O3 Wolf-Rayet (WR) stars were discovered as part of our survey for WRs in the Magellanic Clouds. The WN3/O3s show the emission lines of a high-excitation WN star and the absorption lines of a hot O-type star, but our prior work has shown that the absorption spectrum is intrinsic to the WR star. Their place in the evolution of massive stars remains unclear. Here we investigate the possibility that they are the products of binary evolution. Although these are not WN3+O3~V binaries, they could still harbor unseen companions. To address this possibility, we have conducted a multi-year radial velocity study of six of the nine known WN3/O3s. Our study finds no evidence of statistically significant radial velocity variations, and allows us to set stringent upper limits on the mass of any hypothetical companion star: for probable orbital inclinations, any companion with a period less than 100 days must have a mass less than 2Mo. For periods less than 10 days, any companion would have to have a mass less than 1Mo. We argue that scenarios where any such companion is a compact object are unlikely. The absorption lines indicate a normal projected rotational velocity, making it unlikely that these stars evolved with the aid of a companion star that has since merged. The modest rotation also suggests that these stars are not the result of homogenous evolution. Thus it is likely that these stars are a normal but short-lived stage in the evolution of massive stars., Comment: Astrophysical Journal in press

We present the final results of an imaging and spectroscopic search for stars in the Large Magellanic Cloud (LMC) with C II 7231, 7236 emission lines. The goal is to identify and study [WC11] stars, the coolest of the low-mass Wolf-Rayet sequence, and a subset of central stars of planetary nebulae where the C II lines are known to be especially prominent. A recent serendipitous discovery of an LMC [WC11] raised the possibility that these objects, although difficult to identify, might in fact be more common than previously believed. Several new members of this rare class have been found in this survey. It now seems clear, however, that a significant number of these stars are not hiding amongst the general [WC] population. We point out that the C II doublet intensity ratio observed in our spectra proves to neatly divide the objects into two distinct groups, with the C II emission likely originating from either the stellar wind or a surrounding nebula. The physics of the C II emission mechanism correctly explains this bifurcation. Spectral subtypes are suggested for most of the objects. The numerous spectroscopic clues now available for these objects should facilitate future detailed modeling., Comment: Accepted for publication in The Astrophysical Journal

Mass-loss in red supergiants (RSGs) is generally recognized to be episodic, but mass-loss prescriptions fail to reflect this. Evolutionary models show that the total amount of mass lost during this phase determines if these stars evolve to warmer temperatures before undergoing core collapse. The current Geneva evolutionary models mimic episodic mass loss by enhancing the quiescent prescription rates whenever the star's outer layers exceed the Eddington luminosity by a large factor. This results in a 20 solar-mass model undergoing significantly more mass loss during the RSG phase than it would have otherwise, but has little effect on models of lower masses. We can test the validity of this approach observationally by measuring the proportion of high-luminosity RSGs to that predicted by the models. To do this, we use our recent luminosity-limited census of RSGs in M31 and M33, making modest improvements to membership, and adopting extinctions based on the recent panchromatic M31 and M33 Hubble surveys. We then compare the proportions of the highest luminosity RSGs found to that predicted by published Geneva models, as well as to a special set of models computed without the enhanced rates. We find good agreement with the models which include the supra-Eddington enhanced mass loss. The models with lower mass-loss rates predict a larger fraction of high-luminosity RSGs than observed, and thus can be ruled out. We also use these improved data to confirm that the upper luminosity limit of RSGs is log L/Lo~5.4, regardless of metallicity, using our improved data on M31 and M33 plus previous results on the Magellanic Clouds., Comment: Accepted for publication in the Astrophysical Journal. Revised version includes an additional reference

Are WO-type Wolf Rayet (WR) stars in the final stage of massive star evolution before core-collapse? Although WC- and WO-type WRs have very similar spectra, WOs show a much stronger O VI $\lambda \lambda$3811,34 emission-line feature. This has usually been interpreted to mean that WOs are more oxygen rich than WCs, and thus further evolved. However, previous studies have failed to model this line, leaving the relative abundances uncertain, and the relationship between the two types unresolved. To answer this fundamental question, we modeled six WCs and two WOs in the LMC using UV, optical, and NIR spectra with the radiative transfer code CMFGEN in order to determine their physical properties. We find that WOs are not richer in oxygen; rather, the O VI feature is insensitive to the abundance. However, the WOs have a significantly higher carbon and lower helium content than the WCs, and hence are further evolved. A comparison of our results with single-star Geneva and binary BPASS evolutionary models show that while many properties match, there is more carbon and less oxygen in the WOs than either set of evolutionary model predicts. This discrepancy may be due to the large uncertainty in the $^{12}$C+$^4$He$\rightarrow^{16}$O nuclear reaction rate; we show that if the Kunz et al. rate is decreased by a factor of 25-50%, then there would be a good match with the observations. It would also help explain the LIGO/VIRGO detection of black holes whose masses are in the theoretical upper mass gap., Comment: 55 pages, 22 figures, Accepted into ApJ

Using archival near-IR photometry, we identify 51 of the K-band brightest red supergiants (RSGs) in NGC 6822 and compare their physical properties with stellar evolutionary model predictions. We first use Gaia parallax and proper motion values to filter out foreground Galactic red dwarfs before constructing a J - K vs. K color-magnitude diagram to eliminate lower-mass asymptotic giant branch star contaminants in NGC 6822. We then cross-match our results to previously spectroscopically confirmed RSGs and other NGC 6822 content studies and discuss our overall completeness, concluding that radial velocity alone is an insufficient method of determining membership in NGC 6822. After transforming the J and K magnitudes to effective temperatures and luminosities, we compare these physical properties with predictions from both the Geneva single-star and Binary Population and Spectral Synthesis (BPASS) single and binary star evolution tracks. We find that our derived temperatures and luminosities match the evolutionary model predictions well, however the BPASS model that includes the effects of binary evolution provides the best overall fit. This revealed the presence of a group of cool RSGs in NGC 6822, suggesting a history of binary interaction. We hope this work will lead to further comparative RSG studies in other Local Group galaxies, opportunities for direct spectroscopic follow-up, and a better understanding of evolutionary model predictions., Comment: AJ, accepted

We present a spectral analysis of four LMC WC-type Wolf-Rayet (WR) stars (BAT99-8, BAT99-9, BAT99-11, and BAT99-52) to shed light on two evolutionary questions surrounding massive stars. The first is: are WO-type WR stars more oxygen enriched than the WC-type stars, indicating further chemical evolution, or are the strong high-excitation oxygen lines in the WO-type stars an indication of higher temperatures. This study will act as a baseline for answering the question of where WO-type stars fall in WR evolution. Each star's spectrum, extending from 1100~\AA\ to 25000~\AA, was modeled using \cmfgen\ to determine the star's physical properties such as luminosity, mass-loss rate, and chemical abundances. The oxygen abundance is a key evolutionary diagnostic, and with higher resolution data and an improved stellar atmosphere code, we found the oxygen abundance to be up to a factor of 5 lower than previous studies. The second evolutionary question revolves around the formation of WR stars: Do they evolve by themselves or is a close companion star necessary for their formation? Using our derived physical parameters, we compared our results to the Geneva single-star evolutionary models and the BPASS binary evolutionary models. We found that both the Geneva solar metallicity models and BPASS LMC metallicity models are in agreement with the four WC-type stars, while the Geneva LMC metallicity models are not. Therefore, these four WC4 stars could have been formed either via binary or single-star evolution.

Despite the many successes that modern massive star evolutionary theory has enjoyed, reproducing the apparent trend in the relative number of red supergiants (RSGs) and Wolf-Rayet (WR) stars has remained elusive. Previous estimates show the RSG/WR ratio decreasing strongly with increasing metallicity. However, the evolutionary models have always predicted a relatively flat distribution for the RSG/WR ratio. In this paper we reexamine this issue, drawing on recent surveys for RSGs and WRs in the Magellanic Clouds, M31, and M33. The RSG surveys have used Gaia astrometry to eliminate foreground contamination, and have separated RSGs from asymptotic giant branch stars using near-infrared colors. The surveys for WRs have utilized interference filter imaging, photometry, and image subtraction techniques to identify candidates, which have then been confirmed spectroscopically. After carefully matching the observational criteria to the models, we now find good agreement in both the single-star Geneva and binary BPASS models with the new observations. The agreement is better when we shift the RSG effective temperatures derived from J-Ks photometry downwards by 200 K in order to agree with the Levesque TiO effective temperature scale. In an appendix we also present a source list of RSGs for the SMC which includes effective temperatures and luminosities derived from near-infrared 2MASS photometry, in the same manner as used for the other galaxies., Comment: Astrophysical Journal, in press

Mid-infrared photometry of the Wolf-Rayet star HD 38030 in the Large Magellanic Cloud from the NEOWISE-R mission show it to have undergone a dust-formation episode in 2018 and the dust to have cooled in 2019-20. New spectroscopy with the MagE spectrograph on the Magellan I Baade Telescope in 2019 and 2020 show absorption lines attributable to a companion of type near O9.7III-IV. We found a significant shift in the radial velocity of the C IV 5801-12 blend compared with the RVs measured in 1984 and 1993. The results combine to suggest that HD 38030 is a colliding-wind binary having short-lived dust formation episodes, like the Galactic systems WR 140 and WR 19, but at intervals in excess of 20 yr., Comment: 8 pages, 6 figures, accepted for publication in the MNRAS

An analysis of the Large Magellanic Cloud (LMC) WC4 star BAT99-9 (HD 32125, FD 4, Brey 7, WS 3) shows that the star still contains photospheric nitrogen. Three N emission features (N V $\lambda\lambda 1238,1242$, N IV $\lambda 1719$, N IV $\lambda\lambda 3479 - 3485$) are unambiguously identified in the spectrum. CMFGEN models of the star yield a N/C ratio of $0.004 \pm 0.002$ (by number) and a C/He ratio of $0.15_{-0.05}^{+0.10}$. Due to the similarity of BAT99-9 to other WC4 stars, and the good fit achieved by CMFGEN to both the classic WC4 spectrum, and the N lines, we argue that the N lines are intrinsic to BAT99-9. An examination of a limited set of rotating models for single star evolution at LMC and Galactic metallicities shows that a model with a Galactic metallicity ($z=0.014$) and a progenitor mass of around $50\,M_\odot$ can have a N/C ratio similar to, or larger than, what we observe for a significant fraction of its lifetime. However, the LMC models ($z=0.006$) are inconsistent with the observations. Both the single and binary BPASS models predict that many WC stars can have a N/C ratio similar to, or larger than, what we observe for a significant fraction of their lifetime. While the binary models cover a wider range of luminosities and provide a somewhat better match to BAT99-9, it is not currently possible to rule out BAT99-9 being formed through single star evolution, given the uncertainties in mass-loss rates, and the treatment of convection and mixing processes., Comment: Accepted for publication in MNRAS

We identify red supergiants (RSGs) in our spiral neighbors M31 and M33 using near-IR (NIR) photometry complete to a luminosity limit of log L/Lo=4.0. Our archival survey data cover 5 deg^2 of M31, and 3 deg^2 for M33, and are likely spatially complete for these massive stars. Gaia is used to remove foreground stars, after which the RSGs can be separated from asymptotic giant branch (AGB) stars in the color-magnitude diagram. The photometry is used to derive effective temperatures and bolometric luminosities via MARCS stellar atmosphere models. The resulting H-R diagrams show superb agreement with the evolutionary tracks of the Geneva evolutionary group. Our census includes 6400 RSGs in M31 and 2850 RSGs in M33 within their Holmberg radii; by contrast, only a few hundred RSGs are known so far in the Milky Way. Our catalog serves as the basis for a study of the RSG binary frequency being published separately, as well as future studies relating to the evolution of massive stars. Here we use the matches between the NIR-selected RSGs and their optical counterparts to show that the apparent similarity in the reddening of OB stars in M31 and M33 is the result of Malmquist bias; the average extinction in M31 is likely higher than that of M33. As expected, the distribution of RSGs follows that of the spiral arms, while the much older AGB population is more uniformly spread across each galaxy's disk., Comment: Accepted for publication in the Astronomical Journal. Revision is to fix minor typo in Table 2, where M31 and M33 temperature equations had been interchanged

The binary fraction of unevolved massive stars is thought to be 70-100% but there are few observational constraints on the binary fraction of the evolved version of a subset of these stars, the red supergiants (RSGs). Here we identify a complete sample of RSGs in the Large Magellanic Cloud (LMC) using new spectroscopic observations and archival UV, IR and broadband optical photometry. We find 4090 RSGs with log L/Lo > 3.5 with 1820 of them having log L/Lo > 4, which we believe is our completeness limit. We additionally spectroscopically confirmed 38 new RSG+B star binaries in the LMC, bringing the total known up to 55. We then estimated the binary fraction using a k-nearest neighbors algorithm that classifies stars as single or binary based on photometry with a spectroscopic sample as a training set. We take into account observational biases such as line-of-sight stars and binaries in eclipse while also calculating model-dependent corrections for RSGs with companions that our observations were not designed to detect. Based on our data, we find an initial result of 13.5 +7.56/-6.67% for RSGs with O or B-type companions. Using the Binary Population and Spectral Synthesis (BPASS) models to correct for unobserved systems, this corresponds to a total RSG binary fraction of 19.5 +7.6/-6.7%. This number is in broad agreement with what we would expect given an initial OB binary distribution of 70%, a predicted merger fraction of 20-30% and a binary interaction fraction of 40-50%., Comment: ApJ, accepted

We present a narrow-band imaging survey of the Large Magellanic Cloud, designed to isolate the C II $\lambda\lambda$7231, 7236 emission lines in objects as faint as $m_{\lambda7400}\sim18$. The work is motivated by the recent serendipitous discovery in the LMC of the first confirmed extragalactic [WC11] star, whose spectrum is dominated by C II emission, and the realization that the number of such objects is currently largely unconstrained. The survey, which imaged $\sim$50$~$deg$^2$ using on-band and off-band filters, will significantly increase the total census of these rare stars. In addition, each new LMC [WC] star has a known luminosity, a quantity quite uncertain in the Galactic sample. Multiple known C II emitters were easily recovered, validating the survey design. We find 38 new C II emission candidates; spectroscopy of the complete sample will be needed to ascertain their nature. In a preliminary spectroscopic reconnaissance, we observed three candidates, finding C II emission in each. One is a new [WC11]. Another shows both the narrow C II emission lines characteristic of a [WC11], but also broad emission of C IV, O V, and He II characteristic of a much hotter [WC4] star; we speculate that this is a binary [WC]. The third object shows weak C II emission, but the spectrum is dominated by a dense thicket of strong absorption lines, including numerous O II transitions. We conclude it is likely an unusual hot, hydrogen-poor post-AGB star, possibly in transition from [WC] to white dwarf. Even lacking a complete spectroscopic program, we can infer that late [WC] stars do not dominate the central stars of LMC planetary nebulae, and that the detected C II emitters are largely of an old population., Comment: Accepted for publication in the Astrophysical Journal, 2020

We introduce TensorFlow Quantum (TFQ), an open source library for the rapid prototyping of hybrid quantum-classical models for classical or quantum data. This framework offers high-level abstractions for the design and training of both discriminative and generative quantum models under TensorFlow and supports high-performance quantum circuit simulators. We provide an overview of the software architecture and building blocks through several examples and review the theory of hybrid quantum-classical neural networks. We illustrate TFQ functionalities via several basic applications including supervised learning for quantum classification, quantum control, simulating noisy quantum circuits, and quantum approximate optimization. Moreover, we demonstrate how one can apply TFQ to tackle advanced quantum learning tasks including meta-learning, layerwise learning, Hamiltonian learning, sampling thermal states, variational quantum eigensolvers, classification of quantum phase transitions, generative adversarial networks, and reinforcement learning. We hope this framework provides the necessary tools for the quantum computing and machine learning research communities to explore models of both natural and artificial quantum systems, and ultimately discover new quantum algorithms which could potentially yield a quantum advantage., Comment: 56 pages, 34 figures, many updates throughout the manuscript, several new sections are added

We present optical spectrophotometry of the red supergiant Betelgeuse from 2020 February 15, during its recent unprecedented dimming episode. By comparing this spectrum to stellar atmosphere models for cool supergiants, as well as spectrophotometry of other Milky Way red supergiants, we conclude that Betelgeuse has a current effective temperature of 3600 +/- 25 K. While this is slightly cooler than previous measurements taken prior to Betelgeuse's recent lightcurve evolution, this drop in effective temperature is insufficient to explain Betelgeuse's recent optical dimming. We propose that episodic mass loss and an increase in the amount of large-grain circumstellar dust along our sightline to Betelgeuse is the most likely explanation for its recent photometric evolution., Comment: 13 pages, 4 figures; accepted for publication in ApJ Letters

The mass-loss rates of red supergiant stars (RSGs) are poorly constrained by direct measurements, and yet the subsequent evolution of these stars depends critically on how much mass is lost during the RSG phase. In 2012 the Geneva evolutionary group updated their mass-loss prescription for RSGs with the result that a 20 solar mass star now loses 10x more mass during the RSG phase than in the older models. Thus, higher mass RSGs evolve back through a second yellow supergiant phase rather than exploding as Type II-P supernovae, in accord with recent observations (the so-called "RSG Problem"). Still, even much larger mass-loss rates during the RSG phase cannot be ruled out by direct measurements of their current dust-production rates, as such mass-loss is episodic. Here we test the models by deriving a luminosity function for RSGs in the nearby spiral galaxy M31 which is sensitive to the total mass loss during the RSG phase. We carefully separate RSGs from asymptotic giant branch stars in the color-magnitude diagram following the recent method exploited by Yang and collaborators in their Small Magellanic Cloud studies. Comparing our resulting luminosity function to that predicted by the evolutionary models shows that the new prescription for RSG mass-loss does an excellent job of matching the observations, and we can readily rule out significantly larger values., Comment: ApJ, accepted

Wolf-Rayet stars (WRs) represent the end of a massive star's life as it is about to turn into a supernova. Obtaining complete samples of such stars across a large range of metallicities poses observational challenges, but presents us with an exacting way to test current stellar evolutionary theories. A technique we have developed and refined involves interference filter imaging combined with image subtraction and crowded-field photometry. This helps us address one of the most controversial topics in current massive star research: the relative importance of binarity in the evolution of massive stars and formation of WRs. Here we discuss the current state of the field, including how the observed WR populations match with the predictions of both single and binary star evolutionary models. We end with what we believe are the most important next steps in WR research., Comment: Accepted to MDPI Galaxy special issue, "Luminous Stars in Nearby Galaxies." Editor: Roberta Humphreys

We present the detection of the first candidate colliding-wind binary (CWB) in M33, located in the giant H II region NGC 604. The source was first identified in archival {\it Chandra} imaging as a relatively soft X-ray point source, with the likely primary star determined from precise astrometric alignment between archival {\it Hubble Space Telescope} and {\it Chandra} imaging. The candidate primary star in the CWB is classified for the first time in this work as a carbon-rich Wolf-Rayet star with a likely O star companion based on spectroscopy obtained from Gemini-North. We model the X-ray spectrum using {\it Chandra} and {\it XMM-Newton} observations, and find the CWB is well-fit as a $\sim$ 1 keV thermal plasma with a median unabsorbed luminosity in the 0.5--2.0 keV band of $L_{\rm X}$ $\sim$ 3 $\times$ 10$^{35}$ erg s$^{-1}$, making this source among the brightest of CWBs observed to date. We present a long term light curve for the candidate CWB from archival {\it Chandra} and {\it XMM-Newton} observations, and discuss the constraints placed on the binary by this light curve, as well as the X-ray luminosity at maximum. Finally, we compare this candidate CWB in M33 to other well-studied, bright CWBs in the Galaxy and Magellanic Clouds, such as $\eta$ Car., Comment: 21 pages, 8 figures, 4 tables, Accepted for publication in ApJ

Structured information about entities is critical for many semantic parsing tasks. We present an approach that uses a Graph Neural Network (GNN) architecture to incorporate information about relevant entities and their relations during parsing. Combined with a decoder copy mechanism, this approach provides a conceptually simple mechanism to generate logical forms with entities. We demonstrate that this approach is competitive with the state-of-the-art across several tasks without pre-training, and outperforms existing approaches when combined with BERT pre-training., Comment: ACL 2019

We report the discovery of 11 newly found quasars behind the stellar disks of the spiral galaxies M31 and M33 in the fields covered by the Local Group Galaxy Survey. Their redshifts range from 0.37 to 2.15. Most are X-ray, UV, and IR sources. We also report the discovery of 5 normal background galaxies. Most of these objects were observed owing to their anomalous colors, as part of a program (reported elsewhere) to confirm spectroscopically candidate red supergiant plus B star binaries; others were discovered as part of our identification of early-type massive stars based upon their optical colors. There are 15 previously known quasars in the same fields, for a grand total of 26, 15 behind M31 and 11 behind M33. Of these, only eight were discovered as part of surveys for quasars; the rest were found accidentally. The quasars are well distributed in the M31 and M33 fields, except for the inner regions, and have the potential for being good probes of the interstellar medium in these stellar disks, as well as serving as zero-point calibrators for Gaia parallaxes., Comment: Accepted by the Astronomical Journal

The percentage of massive main sequence OB stars in binary systems is thought to be as high as 100%. However, very few Galactic binary red supergiants (RSGs) have been identified, despite the fact that these stars are the evolved descendants of OB stars. As shown in our recent paper, binary RSGs will likely have B-type companions, as dictated by stellar evolution considerations. Such a system will have a very unique photometric signature due to the shape of the spectral energy distribution. Using photometric cutoffs it should therefore be possible to detect candidate RSG+B star binary systems. Here we present our spectoscopic follow-up observations of such candidates. Out of our initial list of 280 candidates in M31 and M33, we observed 149 and confirmed 63 as newly discovered RSG+B star binary systems. Additional spectra of four candidate systems in the Small Magellanic Cloud confirmed all of them as new RSG+B star binaries including the first known RSG+Be star system. By fitting BSTAR06 and MARCS model atmospheres to the newly-obtained spectra we place estimates on the temperatures and subtypes of both the B stars and RSGs. Overall, we have found 87 new RSG+B star binary systems in M31, M33 and the Small and Large Magellanic Clouds. Our future studies are aimed at determining the binary fraction of RSGs., Comment: Accepted to ApJ

In the standard view of massive star evolution, luminous blue variables (LBVs) are transitional objects between the most massive O-type stars and Wolf-Rayet (WR) stars. With short lifetimes, these stars should all be found near one another. A recent study of LBVs in the Large Magellanic Cloud (LMC) found instead that LBVs are considerably more isolated than either O-type stars or WRs, with a distribution intermediate between that of the WRs and red supergiants (RSGs). A similar study, using a more restricted sample of LBVs, reached the opposite conclusion. Both studies relied upon the distance to the nearest spectroscopically identified O-type star to define the degree of isolation. However, our knowledge of the spectroscopic content of the LMC is quite spotty. Here we re-examine the issue using carefully defined photometric criteria to select the highest mass unevolved stars ("bright blue stars," or BBSs), using spatially complete photometric catalogs of the LMC, M31, and M33. Our study finds that the LBVs are no more isolated than BBSs or WRs. This result holds no matter which sample of LBVs we employ. A statistical test shows that we can rule out the LBVs having the same distribution as the RSGs, which are about 2x more isolated. We demonstrate the robustness of our results using the second-closest neighbor. Furthermore, the majority of LBVs in the LMC are found in or near OB associations as are the BBS and WRs; the RSGs are not. We conclude that the spatial distribution of LBVs therefore is consistent with the standard picture of massive star evolution., Comment: Published by the Astronomical Journal, 6 figures, 3 tables, edited to make consistent with published version

New evidence provided by the Gaia satellite places the location of the runaway star J01020100-7122208 in the halo of the Milky Way (MW) rather than in the Small Magellanic Cloud as previously thought. We conduct a reanalysis of the star's physical and kinematic properties, which indicates that the star may be an even more extraordinary find than previously reported. The star is a 180 Myr old 3-4 Mo G5-8 bright giant, with an effective temperature of 4800+/-100 K, a metallicity of {Fe/H]=-0.5, and a luminosity of log L/Lo=2.70+/-0.20 dex. A comparison with evolutionary tracks identifies the star as being in a giant or early asymptotic giant branch stage. The proper motion, combined with the previously known radial velocity, yields a total Galactocentric space velocity of 296 km/s. The star is currently located 6.4 kpc below the plane of the Milky Way, but our analysis of its orbit shows it passed through the disk ~25 Myr ago. The star's metallicity and age argue against it being native to the halo, and we suggest that the star was likely ejected from the disk. We discuss several ejection mechanisms, and conclude that the most likely scenario is ejection by the Milky Way's central black hole based upon our analysis of the star's orbit. The identification of the large radial velocity of J01020100-7122208 came about as a happenstance of it being seen in projection with the SMC, and we suggest that many similar objects may be revealed in Gaia data., Comment: Astronomical Journal, in press

We summarize the results of our four year survey searching for Wolf-Rayet (WR) stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). Over the course of this survey we've discovered 15 new WRs and 12 Of-type stars. In this last year we discovered two rare Of-type stars: an O6.5f?p and an O6nfp in addition to the two new Of?p stars discovered in our first year and the three Onfp stars discovered in our second and third years. However, even more exciting was our discovery of a new type of WR, ones we are calling WN3/O3s due to their spectroscopic signatures. We describe the completeness limits of our survey and demonstrate that we are sensitive to weak-lined WRs several magnitudes fainter than any we have discovered, arguing that there is not a population of fainter WRs waiting to be discovered. We discuss the nature of the WN3/O3s, summarizing the results of our extensive spectroscopy and modeling. We also examine the important claim made by others that the WN3/O3s are isolated compared to other massive stars. We find that if we use a more complete sample of reference massive stars, the WN3/O3s show the same spatial distribution as other early WNs, consistent with a common origin. Finally, we use this opportunity to present the "Fifth Catalog of LMC Wolf-Rayet Stars," which includes revised coordinates and updated spectral types for all 154 known LMC WRs., Comment: accepted to ApJ

We recently discovered a yellow supergiant (YSG) in the Small Magellanic Cloud (SMC) with a heliocentric radial velocity of ~300 km/s which is much larger than expected for a star in its location in the SMC. This is the first runaway YSG ever discovered and only the second evolved runaway star discovered in a different galaxy than the Milky Way. We classify the star as G5-8I, and use de-reddened broad-band colors with model atmospheres to determine an effective temperature of 4700+/-250K, consistent with what is expected from its spectral type. The star's luminosity is then L/Lo ~ 4.2+/-0.1, consistent with it being a ~30Myr 9Mo star according to the Geneva evolution models. The star is currently located in the outer portion of the SMC's body, but if the star's transverse peculiar velocity is similar to its peculiar radial velocity, in 10Myr the star would have moved 1.6 degrees across the disk of the SMC, and could easily have been born in one of the SMC's star-forming regions. Based on its large radial velocity, we suggest it originated in a binary system where the primary exploded as a supernovae thus flinging the runaway star out into space. Such stars may provide an important mechanism for the dispersal of heavier elements in galaxies given the large percentage of massive stars that are runaways. In the future we hope to look into additional evolved runaway stars that were discovered as part of our other past surveys., Comment: accepted by AJ

The nearby galaxies of the Local Group can act as our laboratories in helping to bridge the gap between theory and observations. In this review we will describe the complications of identifying samples of OB stars, yellow and red supergiants, and Wolf-Rayet stars, and what we have so far learned from these studies., Comment: To appear in Philosophical Transactions A, from the conference "Bridging the Gap: from Massive Stars to Supernovae."

As part of a search for Wolf-Rayet (WR) stars in the Magellanic Clouds, we have discovered a new type of WR star in the Large Magellanic Cloud (LMC). These stars have both strong emission lines, as well as He ii and Balmer absorption lines and spectroscopically resemble a WN3 and O3V binary pair. However, they are visually too faint to be WN3+O3V binary systems. We have found nine of these WN3/O3s, making up ~6% of the population of LMC WRs. Using CMFGEN, we have successfully modeled their spectra as single stars and have compared the physical parameters with those of more typical LMC WNs. Their temperatures are around 100,000 K, a bit hotter than the majority of WN stars (by around 10,000 K) although a few hotter WNs are known. The abundances are what you would expect for CNO equilibrium. However, most anomalous are their mass-loss rates which are more like that of an O-type star than a WN star. While their evolutionary status is uncertain, their low mass-loss rates and wind velocities suggest that they are not products of homogeneous evolution. It is possible instead that these stars represent an intermediate stage between O stars and WNs. Since WN3/O3 stars are unknown in the Milky Way, we suspect that their formation depends upon metallicity, and we are investigating this further by a deep survey in M33, which posses a metallicity gradient., Comment: ApJ, accepted

We summarize here recent work in identifying and characterizing red supergiants (RSGs) in the galaxies of the Local Group., Comment: To appear in IAU 329, The Lives and Death-throes of Massive Stars, ed. J. J. Eldridge

For the past three years we have been conducting a survey for WR stars in the Large and Small Magellanic Clouds (LMC, SMC). Our previous work has resulted in the discovery of a new type of WR star in the LMC, which we are calling WN3/O3. These stars have the emission-line properties of a WN3 star (strong N V but no N IV), plus the absorption-line properties of an O3 star (Balmer hydrogen plus Pickering He II but no He I). Yet these stars are 15x fainter than an O3 V star would be by itself, ruling out these being WN3+O3 binaries. Here we report the discovery of two more members of this class, bringing the total number of these objects to 10, 6.5% of the LMC's total WR population. The optical spectra of nine of these WN3/O3s are virtually indistinguishable from each other, but one of the newly found stars is significantly different, showing a lower excitation emission and absorption spectrum (WN4/O4-ish). In addition, we have newly classified three unusual Of-type stars, including one with a strong C III 4650 line, and two rapidly rotating "Oef" stars. We also "rediscovered" a low mass x-ray binary, RX J0513.9-6951, and demonstrate its spectral variability. Finally, we discuss the spectra of ten low priority WR candidates that turned out not to have He II emission. These include both a Be star and a B[e] star., Comment: ApJ, in press

We investigate Wolf-Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point in the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4m Mayall Telescope at Kitt Peak National Observatory and the 6.5m MMT. We identify 21 sources with significantly detected WR signatures, which we term "emerging WR clusters." WR features are detected in $\sim$50% of the radio-selected sample, and thus we find that WR stars are commonly present in massive star clusters currently emerging. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process., Comment: To appear in the Astrophysical Journal. 55 pages, 20 figures

We investigate the red supergiant (RSG) population of M31, obtaining radial velocities of 255 stars. These data substantiate membership of our photometrically-selected sample, demonstrating that Galactic foreground stars and extragalactic RSGs can be distinguished on the basis of B-V, V-R two-color diagrams. In addition, we use these spectra to measure effective temperatures and assign spectral types, deriving physical properties for 192 RSGs. Comparison with the solar-metallicity Geneva evolutionary tracks indicates astonishingly good agreement. The most luminous RSGs in M31 are likely evolved from 25-30 Mo stars, while the vast majority evolved from stars with initial masses of 20 Mo or less. There is an interesting bifurcation in the distribution of RSGs with effective temperatures that increases with higher luminosities, with one sequence consisting of early K-type supergiants, and with the other consisting of M-type supergiants that become later (cooler) with increasing luminosities. This separation is only partially reflected in the evolutionary tracks, although that might be due to the mis-match in metallicities between the solar Geneva models and the higher-than-solar metallicity of M31. As the luminosities increase the median spectral type also increases; i.e., the higher mass RSGs spend more time at cooler temperatures than do those of lower luminosities, a result which is new to this study. Finally we discuss what would be needed observationally to successfully build a luminosity function that could be used to constrain the mass-loss rates of RSGs as our Geneva colleagues have suggested., Comment: Accepted for publication in the Astronomical Journal

We describe our spectroscopic follow-up to the Local Group Galaxy Survey (LGGS) photometry of M31 and M33. We have obtained new spectroscopy of 1895 stars, allowing us to classify 1496 of them for the first time. Our study has identified many foreground stars, and established membership for hundreds of early- and mid-type supergiants. We have also found 9 new candidate Luminous Blue Variables and a previously unrecognized Wolf-Rayet star. We republish the LGGS M31 and M33 catalogs with improved coordinates and including spectroscopy from the literature and our new results. The spectroscopy in this paper is responsible for the vast majority of the stellar classifications in these two nearby spiral neighbors. The most luminous (and hence massive) of the stars in our sample are early-type B supergiants, as expected; the more massive O stars will be fainter visually, and thus mostly remain unobserved so far. The majority of the unevolved stars in our sample are in the 20-40Mo range., Comment: Astronomical Journal, in press. Full versions of Table 5 and Table 6 can be obtained from http://www.lowell.edu/users/massey/table5full.txt and http://www.lowell.edu/users/massey/table6full.txt