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Abstract We present an analysis of ∼235 ks of Chandra observations obtained over ∼19 yr of the nearby dwarf starburst galaxy IC 10 in order to study the X-ray variability and X-ray luminosity function (XLF) of its X-ray binary (XRB) population. We identify 23 likely XRBs within the Two Micron All Sky SurveyK_Sisophotal radius and find the distributions of their dynamic ranges and duty cycles are consistent with a young, high-mass XRB (HMXB) population dominated by supergiant-fed systems, consistent with previous work. In general, we find that brighter HMXBs (those withL_X≳ several ×10³⁶erg s⁻¹) have higher duty cycles (i.e., are more persistent X-ray sources) than fainter objects, and the dynamic ranges of the sgHMXBs in the lower-metallicity environment of IC 10 are higher than what is observed for comparable systems in the Milky Way. After filtering out foreground stars on the basis of Gaia parallaxes, we construct, for the first time, the XLF of IC 10. We then use the XLF to model the star formation history of the galaxy, finding that a very recent (3–8 Myr) burst of star formation with a rate of ∼0.5M_⊙yr⁻¹is needed to adequately explain the observed bright end (L_X∼ 10³⁷erg s⁻¹) of the HMXB XLF. 

Abstract We report the observations of two self-lensing pulses from KIC 12254688 in Transiting Exoplanet Survey Satellite (TESS) light curves. This system, containing an F2V star and white-dwarf companion, was among the first self-lensing binary systems discovered by the Kepler Space Telescope over the past decade. Each observed pulse occurs when the white dwarf transits in front of its companion star, gravitationally lensing the star’s surface, thus making it appear brighter to a distant observer. These two pulses are the very first self-lensing events discovered in TESS observations. We describe the methods by which the data were acquired and detrended, as well as the best-fit binary parameters deduced from our self-lensing+radial velocity model. We highlight the difficulties of finding new self-lensing systems with TESS, and we discuss the types of self-lensing systems that TESS may be more likely to discover in the future. 

ABSTRACT We present a statistical analysis of the He ii 4686 emission line in the spectra of the black hole and Wolf–Rayet (WR) star of the high-mass X-ray binary IC10 X-1. This line is visibly skewed, and the third moment (skewness) varies with the binary’s orbital phase. We describe a new method of extracting such weak/faint features lying barely above a noisy continuum. Using the moments of these features, we have been able to decompose these skewed lines into two symmetric Gaussian profiles as a function of the orbital phase. The astrophysical implications of this decomposition are significant due to the complex nature of wind–accretion stream interactions in such binary systems. Previous studies have already shown a 0.25 phase lag in the radial velocity curve of the star and the X-ray eclipse, which indicates that the He ii emitters might be in the stellar wind, hence not tracing the star’s orbital motion. Results from this work further suggest the existence of two separate emitting regions, one in the stellar wind in the shadow of the WR star and another in the accretion stream that impacts the black hole’s outer accretion disc; and the observed skewed He ii lines can be reproduced by superposition of the two corresponding time-dependent Gaussian emission profiles. 

Abstract IC 10 X-1 is an eclipsing high-mass X-ray binary containing a stellar-mass black hole (BH) and a Wolf–Rayet (WR) donor star with an orbital period ofP= 34.9 hr. This binary belongs to a group of systems that can be the progenitors of gravitational-wave sources; hence understanding the dynamics of systems such as IC 10 X-1 is of paramount importance. The prominent Heii4686 emission line (previously used in mass estimates of the BH) is out of phase with the X-ray eclipse, suggesting that this line originates somewhere in the ionized wind of the WR star or in the accretion disk. We obtained 52 spectra from the GEMINI/GMOS archive, observed between 2001 and 2019. We analyzed the spectra both individually, and after binning them by orbital phase to improve the signal-to-noise ratio. The radial-velocity curve from the stacked data is similar to historical results, indicating the overall parameters of the binary have remained constant. However, the Heiiline profile shows a correlation with the X-ray hardness-ratio values; also, we report a pronounced skewness of the line profile, and the skewness varies with orbital phase. These results support a paradigm wherein the Heiiline tracks structures in the stellar wind that are produced by interactions with the BH’s ionizing radiation and the accretion flow. We compare the observable signatures of two alternative hypotheses proposed in the literature: wind irradiation plus shadowing, and accretion disk hotspot; and we explore how the line-profile variations fit into each of these models. 

IC 10 is a dwarf galaxy in Cassiopeia, located at a distance of 660 kpc, and hosts a young stellar population, a large number of Wolf–Rayet stars, and a large number of massive stars in general. Utilizing a series of 11 Chandra observations (spanning 2003–2021, with a total exposure of 235.1 ks), 375 point sources of X-ray emission were detected. Similar studies have been conducted earlier in the central region of IC 10. Here, we consider all regions covered by Chandra-ACIS. By comparing our catalog of X-ray sources with a published optical catalog, we found that 146 sources have optical counterparts. We also created a list of 60 blue supergiant (SG) candidates with X-ray binary (XRB) companions by using an optical color–magnitude selection criterion to isolate the blue SGs. Blue SG-XRBs form a major class of progenitors of double-degenerate binaries. Hence, their numbers are an important factor in modeling the rate of gravitational-wave sources. Identifying the nature of individual sources is necessary as it paves the way toward a comprehensive census of XRBs in IC 10, thus enabling meaningful comparisons with other Local Group galaxies exhibiting starbursts, such as the Magellanic Clouds. 

The extragalactic high-mass X-ray binary IC 10 X-2 has been detected in X-ray outburst by Chandra on October 30, 2025. Follow-up observations are requested, specifically: (1) Visible-light spectroscopy to capture the H & alpha; line, which may show a broad or double-peaked structure revealing whether the mass donor has a circumstellar disk or other outflow. 

This thesis presents a comprehensive investigation into the stellar populations and blue supergiant high-mass X-ray binaries (BSG-HMXBs) in the dwarf star-forming galaxy IC 10. The study is motivated by two primary objectives: firstly, to conduct a detailed analysis of the blue supergiant x-ray binary population in IC 10, and secondly, to explore the properties of IC 10 X-1, the brightest source in the galaxy, which is identified as a high mass x-ray binary containing a Wolf-Rayet and black hole. The dwarf galaxy in Cassiopeia, IC 10, located in “close” proximity of 660 kpc, captivates astronomers with its young stellar population, abundant Wolf-Rayet stars, and the presence of massive stars in general. Leveraging a series of space-based X-ray telescope (Chandra) observations, we have identified 375 X-ray point sources. Correlating our list of x-ray sources with published optical catalogs we found those having an optical counterpart. Applying an optical color-magnitude selection to isolate blue supergiant stars, we find the final list of intriguing blue supergiants in a compact-object(x-ray) binary. The ongoing starburst in IC 10 has given rise to a diverse collection of exotic compact-object binaries, including IC 10 X-1 (a Wolf-Rayet and Blackhole high mass x-ray binary) and IC 10 X-2 (a Blue supergiant fast x-ray transient). We have also used GEMINI/GMOS optical spectroscopy to enable multi-wavelength characterization of these BSG sources. Furthermore, our investigation into IC 10 X-1 reveals surprising findings regarding its X-ray emission and orbital dynamics. Through multi-wavelength analysis combining optical radial velocity (RV) curves and X-ray eclipse lightcurves, we uncover a quarter phase offset between these two observational features. IC 10 X-1 is a blackhole+Wolf-Rayet (BH+WR) high mass X-ray binary with an orbital period of 34.9 hrs. The BH mass is currently unconstrained, as the BH accretion disk irradiates the WR wind and alters the ionization structure of spectral line formation regions near the WR star. This alteration of the WR wind geometry masquerades as the classic binary RV curve. To understand the nature of this complex system, we perform a detailed multi-wavelength study using optical spectroscopy (GEMINI/GMOS), X-ray phase-resolved spectroscopy (Chandra), and x-ray lightcurve analysis (Chandra+Swift+XMM), aiming to elucidate the orbital period derivative and refine our understanding of the system’s binary parameters and physical nature. Blue SG-XRBs include a major class of progenitors of double-degenerate binaries, hence their numbers are an important factor in modeling the rate of gravitational-wave sources. Identifying the nature of individual sources is a slow and difficult process, but ultimately necessary as it paves the way toward a comprehensive census of X-ray binaries (XRBs), enabling meaningful comparisons with other galaxies, for example, the Magellanic Clouds.