Search

We report the results from a pilot study to search for black holes and other dark companions in binary systems using direct imaging with SHARK-VIS and the iLocater pathfinder "Lili" on the Large Binocular Telescope. Starting from known single-lined spectroscopic binaries, we select systems with high mass functions that could host dark companions and whose spectroscopic orbits indicate a projected orbital separation $\geq 30$ mas. For this first exploration, we selected four systems (HD 137909, HD 104438, HD 117044, and HD 176695). In each case, we identify a luminous companion and measure the flux ratio and angular separation. However, two of the systems (HD 104438 and HD 176695) are not consistent with simple binary systems and are most likely hierarchical triples. The observed companions rule out a massive compact object for HD 137909, HD 117044, and HD 176695. HD 104438 requires further study because the identified star cannot be responsible for the RV orbit and is likely a dwarf tertiary companion. The SHARK-VIS observation was taken near pericenter, and a second image near apocenter is needed to discriminate between a closely separated luminous secondary and a compact object. We show how the combination of RVs and direct imaging can be used to constrain the orbital inclination and companion mass, and discuss the potential of high resolution direct imaging surveys to identify and confirm non-interacting compact object candidates., Comment: 23 pages, 11 figures. Submitted to ApJ

Precise and accurate mass and radius measurements of evolved stars are crucial to calibrating stellar models. Stars in detached eclipsing binaries (EBs) are excellent potential calibrators because their stellar parameters can be measured with fractional uncertainties of a few percent, independent of stellar models. The All-Sky Automated Survey for Supernovae (ASAS-SN) has identified tens of thousands of EBs, >35,000 of which were included in the ASAS-SN eclipsing binaries catalog. Here, we select eight EBs from this sample that contain giants based on their Gaia colors and absolute magnitudes. We use LBT/PEPSI, APF, and CHIRON to obtain multi-epoch spectra of these binaries and measure their radial velocities using two-dimensional cross-correlation methods. We simultaneously fit the ASAS-SN light curves and the radial velocities with PHOEBE to derive accurate and precise masses and radii with fractional uncertainties of $\lesssim 3\%$. For four systems, we also include Transiting Exoplanet Survey Satellite (TESS) light curves in our PHOEBE models, which significantly improves the radius determinations. In seven of our systems, both components have evolved off of the main sequence, and one system has a giant star component with a main sequence, Sun-like companion. Finally, we compare our mass and radius measurements to single-star evolutionary tracks and distinguish between systems that are first ascent red giant branch stars and those that are likely core helium-burning stars., Comment: 25 pages, 18 figures. Submitted to The Open Journal of Astrophysics

We present the second results from Citizen ASAS-SN, a citizen science project for the All-Sky Automated Survey for Supernovae (ASAS-SN) hosted on the Zooniverse platform. Citizen ASAS-SN tasks users with classifying variable stars based on their light curves. We started with 94975 new variable candidates and identified 4432 new variable stars. The users classified the new variables as 841 pulsating variables, 2995 rotational variables, 350 eclipsing binaries, and 246 unknown variables. We found 68% user agreement for user-classified pulsating variables, 51% for rotational variables, and 77% for eclipsing binaries. We investigate user statistics and compare new variables to known variables. We present a sample of variables flagged as interesting or unusual., Comment: 10 pages, 10 figures

We present a model to estimate the average primary masses, companion mass ranges, the inclination limit for recognizing a rotational variable, and the primary mass spreads for populations of binary stars. The model fits a population's binary mass function distribution and allows for a probability that some mass functions are incorrectly estimated. Using tests with synthetic data, we assess the model's sensitivity to each parameter, finding that we are most sensitive to the average primary mass and the minimum companion mass, with less sensitivity to the inclination limit and little to no sensitivity to the primary mass spread. We apply the model to five populations of binary spotted rotational variables identified in ASAS-SN, computing their binary mass functions using RV data from APOGEE. Their average primary mass estimates are consistent with our expectations based on their CMD locations ($\sim0.75 M_{\odot}$ for lower main sequence primaries and $\sim 0.9$--$1.2 M_{\odot}$ for RS CVn and sub-subgiants). Their companion mass range estimates allow companion masses down to $M_2/M_1\simeq0.1$, although the main sequence population may have a higher minimum mass fraction ($\sim0.4$). We see weak evidence of an inclination limit $\gtrsim50^{\circ}$ for the main sequence and sub-subgiant groups and no evidence of an inclination limit in the other groups. No groups show strong evidence for a preferred primary mass spread. We conclude by demonstrating that the approach will provide significantly better estimates of the primary mass and the minimum mass ratio and reasonable sensitivity to the inclination limit with 10 times as many systems., Comment: 10 pages, 7 figures, 4 tables, submitted to MNRAS

We report on spectroscopic and photometric observations of the AM CVn system ASASSN-21br, which was discovered in outburst by the All-Sky Automated Survey for Supernovae in February 2021. The outburst lasted for around three weeks, and exhibited a pronounced brightness dip for $\approx$ 4 days, during which the spectra showed a sudden transition from emission- to absorption-line dominated. Only $\approx$ 60 AM CVn systems with derived orbital periods are found in the Galaxy, therefore increasing the sample of AM CVn systems with known orbital periods is of tremendous importance to (1) constrain the physical mechanisms of their outbursts and (2) establish a better understanding of the low-frequency background noise of future gravitational wave surveys. Time-resolved photometry taken during the outburst of ASASSN-21br showed modulation with a period of around 36.65 minutes, which is likely the superhump or orbital period of the system. Time-resolved spectroscopy taken with the Southern African Large Telescope did not show any sign of periodicity in the He I absorption lines. This is possibly due to the origin of these lines in the outbursting accretion disc, which makes it challenging to retrieve periodicity from the spectral lines. Future follow up spectral observations during quiescence might allow us better constrain the orbital period of ASASSN-21br., Comment: 14 pages, 13 figures, accepted at MNRAS

In the absence of a parallax distance to a pulsar or a surviving binary in a supernova remnant (SNR), distances to Galactic SNRs are generally very uncertain. However, by combining Gaia data with wide field, multi-fiber echelle spectroscopy, it is now possible to obtain accurate distances to many SNRs with limited extinction by searching for the appearance of high velocity CaII or NaI absorption lines in hot stars as a function of distance. We demonstrate this for the SNR S147 using the spectra of 259 luminous, blue stars. We obtain a median distance of 1.37 kpc (1.30 to 1.47 kpc at 90% confidence) that is consistent with the median parallax distance to the pulsar of 1.46 kpc (1.12 to 2.10 kpc at 90% confidence), but with significantly smaller uncertainties. Our distance is also consistent with the distance to the candidate unbound binary companion in this SNR, HD37424. The presence of high velocity absorption lines is correlated with the emission line flux of the SNR but not with the radio flux., Comment: submitted to ApJ

The recent Gaia Focused Product Release contains radial velocity time-series for more than 9,000 Gaia long-period photometric variables. Here we search for binary systems with large radial velocity amplitudes to identify candidates with massive, unseen companions. Eight targets have binary mass function $f(M)>1\ M_\odot$, three of which are eclipsing binaries. The remaining five show evidence of ellipsoidal modulations. We fit spectroscopic orbit models to the Gaia radial velocities, and fit the spectral energy distributions of three targets. For the two systems most likely to host dark companions, J0946 and J1640, we use PHOEBE to fit the ASAS-SN light curves and Gaia radial velocities. The derived companion masses are $>3 M_\odot$, but the high Galactic dust extinctions towards these objects limit our ability to rule out main sequence companions or subgiants hotter than the photometric primaries. These systems are similar to other stellar-mass black hole impostors, notably the Unicorn (V723 Mon) and the Giraffe (2M04123153$+$6738486). While it is possible that J1640 and J0946 are similar examples of stripped giant star binaries, high-resolution spectra can be used to determine the nature of their companions., Comment: 18 pages, 13 figures. Accepted to The Open Journal of Astrophysics

We report the All-Sky Automated Survey for SuperNovae discovery of the tidal disruption event (TDE) ASASSN-23bd (AT 2023clx) in NGC 3799, a LINER galaxy with no evidence of strong AGN activity over the past decade. With a redshift of $z = 0.01107$ and a peak UV/optical luminosity of $(5.4\pm0.4)\times10^{42}$ erg s$^{-1}$, ASASSN-23bd is the lowest-redshift and least-luminous TDE discovered to date. Spectroscopically, ASASSN-23bd shows H$\alpha$ and He I emission throughout its spectral time series, and the UV spectrum shows nitrogen lines without the strong carbon and magnesium lines typically seen for AGN. Fits to the rising ASAS-SN light curve show that ASASSN-23bd started to brighten on MJD 59988$^{+1}_{-1}$, $\sim$9 days before discovery, with a nearly linear rise in flux, peaking in the $g$ band on MJD $60000^{+3}_{-3}$. Scaling relations and TDE light curve modelling find a black hole mass of $\sim$10$^6$ $M_\odot$, which is on the lower end of supermassive black hole masses. ASASSN-23bd is a dim X-ray source, with an upper limit of $L_{0.3-10\,\mathrm{keV}} < 1.0\times10^{40}$ erg s$^{-1}$ from stacking all \emph{Swift} observations prior to MJD 60061, but with soft ($\sim 0.1$ keV) thermal emission with a luminosity of $L_{0.3-2 \,\mathrm{keV}}\sim4\times10^{39}$ erg s$^{-1}$ in \emph{XMM-Newton} observations on MJD 60095. The rapid $(t < 15$ days) light curve rise, low UV/optical luminosity, and a luminosity decline over 40 days of $\Delta L_{40}\approx-0.7$ make ASASSN-23bd one of the dimmest TDEs to date and a member of the growing ``Low Luminosity and Fast'' class of TDEs., Comment: 17 pages, 13 figures, submitted to MNRAS

We present JWST MIRI 5.6, 10 and 21 micron observations of the candidate failed supernova N6946-BH1 along with HST WFPC/IR 1.1 and 1.6 micron data and ongoing optical monitoring data with the LBT. There is a very red, dusty source at the location of the candidate which has only ~10-15% of the luminosity of the progenitor star. The source is very faint in the HST near-IR observations (~10^3 Lsun) and is not optically variable to a limit of ~10^3 Lsun at R-band. The dust is likely silicate and probably has to be dominated by very large grains as predicted for dust formed in a failed SN. The required visual optical depths are modest, so we should begin to have a direct view of the source in the near-IR in only a few years.

We present 307 Type Ia supernova (SN) light curves from the first four years of the TESS mission. We use this sample to characterize the shapes of the early time light curves, measure the rise times from first light to peak, and search for companion star interactions. Using simulations, we show that light curves must have noise $<$10% of the peak to avoid biases in the early time light curve shape, restricting our quantitative analysis to 74 light curves. We find that the mean power law index $t^{\beta_1}$ of the early time light curves is 1.93$\pm$ 0.57 and the mean rise time to peak is 15.7 $\pm$ 3.5 days. We also estimate the underlying population distribution and find a Gaussian component with mean $\beta_1 = 2.29$, width 0.34, and a tail extending to values less than 1.0. We use model comparison techniques to test for the presence of companion interactions. In contrast to recent results in the literature, we find that the data can rarely distinguish between models with and without companion interactions, and caution is needed when claiming detections of early time flux excesses. Nevertheless, we find three high-quality SN light curves that tentatively prefer the addition of a companion interaction model, but the statistical evidence is not robust. We also find two SNe that disfavor the addition of a companion interaction model to a curved power law model. Taking the 74 SNe together, we calculate 3$\sigma$ upper limits on the presence of companion signatures to control for orientation effects that can hide companions in individual light curves. Our results rule out common progenitor systems with companions having Roche lobe radii $>$ 31 R$_{\odot}$ (99.9% confidence level) and disfavor companions having Roche lobe radii $>$ 10 R$_{\odot}$ (95% confidence level). Lastly, we discuss the implications of our results for the intrinsic fraction of single degenerate progenitor systems., Comment: 40 pages, 23 figures, accepted for publication in ApJ. Figure sets for all 307 objects in Figures 3, 13, 14, and 16, can be viewed at https://space.mit.edu/home/faus/snIa_fig_sets/ in advance of the online journal article

The identification and characterization of massive ($\gtrsim 0.8~M_\odot$) white dwarfs is challenging in part due to their low luminosity. Here we present two candidate single-lined spectroscopic binaries, Gaia DR3 4014708864481651840 and 5811237403155163520, with K-dwarf primaries and optically dark companions. Both have orbital periods of $P\sim 0.45$ days and show rotational variability, ellipsoidal modulations, and high-amplitude radial velocity variations. Using light curves from the Transiting Exoplanet Survey Satellite (TESS), radial velocities from ground-based spectrographs, and spectral energy distributions, we characterize these binaries to describe the nature of the unseen companion. We find that both systems are consistent with a massive white dwarf companion. Unlike simple ellipsoidal variables, star spots cause the light curve morphology to change between TESS sectors. We attempt to constrain the orbital inclination using PHOEBE binary light curve models, but degeneracies in the light curves of spotted stars prevent a precise determination. Finally, we search for similar objects using Gaia DR3 and TESS, and comment on these systems in the context of recently claimed compact object binaries., Comment: 17 pages, 15 figures. Submitted to MNRAS

We present the volumetric rates and luminosity functions (LFs) of Type Ia supernovae (SNe Ia) from the $V$-band All-Sky Automated Survey for Supernovae (ASAS-SN) catalogues spanning discovery dates from UTC 2014-01-26 to UTC 2017-12-29. Our standard sample consists of 404 SNe Ia with $m_{V,\mathrm{peak}}<17$ mag and Galactic latitude $|b|>15^{\circ}$. Our results are both statistically more precise and systematically more robust than previous studies due to the large sample size and high spectroscopic completeness. We make completeness corrections based on both the apparent and absolute magnitudes by simulating the detection of SNe Ia in ASAS-SN light curves. We find a total volumetric rate for all subtypes of $R_{\mathrm{tot}}=2.28^{+0.20}_{-0.20}\,\times 10^{4}\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}\,h^{3}_{70}$ for $M_{V,\mathrm{peak}}<-16.5$ mag ($R_{\mathrm{tot}}=1.91^{+0.12}_{-0.12}\,\times 10^{4}\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}\,h^{3}_{70}$ for $M_{V,\mathrm{peak}}<-17.5$ mag) at the median redshift of our sample, $z_{\mathrm{med}}=0.024$. This is in agreement ($1\sigma$) with the local volumetric rates found by previous studies. We also compile luminosity functions (LFs) for the entire sample as well as for subtypes of SNe Ia for the first time. The major subtypes with more than one SN include Ia-91bg, Ia-91T, Ia-CSM, and Ia-03fg with total rates of $R_{\mathrm{Ia-91bg}}=1.4^{+0.5}_{-0.5} \times 10^{3}\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}\,h^{3}_{70}$, $R_{\mathrm{Ia-91T}}=8.5^{+1.6}_{-1.7} \times 10^{2}\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}\,h^{3}_{70}$, $R_{\mathrm{Ia-CSM}}=10^{+7}_{-7}\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}\,h^{3}_{70}$, and $R_{\mathrm{Ia-03fg}}=30^{+20}_{-20}\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}\,h^{3}_{70}$, respectively. We estimate a mean host extinction of $E(V-r)\approx 0.2$ mag based on the shift between our $V$-band and the ZTF $r$-band LFs., Comment: 14 pages, 9 figures, 8 tables, accepted to MNRAS

The progenitor of SN 2023ixf was a $\sim$10$^{4.8}$ to $10^{5.0}\rm ~L_\odot$ star ($\sim$9 to $14 \rm~M_\odot$ at birth) obscured by a dusty $\dot{M} \simeq 10^{-5} \rm~M_\odot~yr^{-1}$ wind with a visual optical depth of $\tau_V \simeq 13$. This is required by the progenitor SED, the post-SN X-ray and H$\alpha$ luminosities, and the X-ray column density estimates. In Large Binocular Telescope (LBT) data spanning 5600 to 400 d before the SN, there is no evidence for optical variability at the level of $\sim$10$^3\rm~L_\odot$ in $R$ band, roughly 3 times the predicted luminosity of the obscured progenitor. This constrains direct observation of any pre-SN optical outbursts where there are LBT observations. However, models of the effects of any pre-SN outburst on the dusty wind show that an outburst of essentially any duration exceeding $\sim$5 times the luminosity of the progenitor would have detectable effects on the dust optical depth for decades. While the dust obscuration here is high, all red supergiants have dusty winds, and the destruction (or formation) of dust by even short-lived transients will always have long term effects on the observed brightness of the star because changes in the dust optical depths after a luminous transient occur very slowly., Comment: 8 pages, 5 figures, submitted to MNRAS on 6/8, comments welcome

We estimate black hole masses (M$_{\rm BH}$) for 14 gravitationally lensed quasars using the Balmer lines along with estimates based on MgII and CIV emission lines for four and two of them, respectively. We compare with results obtained for other lensed quasars. We use spectroscopic data from the Large Binocular Telescope (LBT), Magellan and the Very Large Telescope (VLT) to measure the FWHM of the broad emission lines. Combined with the bolometric luminosity measured from the spectra energy distribution, we estimate M$_{\rm BH}$ including uncertainties from microlensing and variability. We obtain MBH using the single-epoch method from the H$\alpha$ and/or H$\beta$ broad emission lines for 14 lensed quasars, including the first estimates for QJ0158-4325, HE0512-3329 and WFI2026-4536. The masses are typical of non-lensed quasars of similar luminosity, and the implied Eddington ratios are typical. We have increased the sample of lenses with estimates of MBH by 60%., Comment: 16 pages. Submitted to A&A

Dust absorption is invoked in a number of contexts for hiding a star that has survived some sort of transient event from view. Dust formed in a transient is expanding away from the star and, in spherical models, the mass and energy budgets implied by a high optical depth at late times make such models untenable. Concentrating the dust in a disk or torus can in principle hide a source from an equatorial observer using less mass and so delay this problem. However, using axisymmetric dust radiation transfer models with a range of equatorial dust concentrations, we find that this is quite difficult to achieve in practice. The polar optical depth must be either low or high to avoid scattering optical photons to equatorial observers. Most of the emission remains at wavelengths easily observed by JWST, and the equatorial brightness is reduced by at most a factor of ~2 compared to isotropic emission even for equatorial (visual) optical depths of 1000. It is particularly difficult to hide a source with silicate dusts because the absorption feature near 10\ microns frequently leads to the emission being concentrated just bluewards of the feature, near 8 microns., Comment: 11 pages, 10 figures, submitted to MNRAS

We examine the properties of $\sim50,000$ rotational variables from the ASAS-SN survey using distances, stellar properties, and probes of binarity from $\textit{Gaia}$ DR3 and the SDSS APOGEE survey. They have high amplitudes and span a broader period range than previously studied $\textit{Kepler}$ rotators. We find they divide into three groups of main sequence stars (MS1, MS2s, MS2b) and four of giants (G1/3, G2, G4s, and G4b). MS1 stars are slowly rotating (10-30 days), likely single stars with a limited range of temperatures. MS2s stars are more rapidly rotating (days) single stars spanning the lower main sequence up to the Kraft break. There is a clear period gap (or minimum) between MS1 and MS2s, similar to that seen for lower temperatures in the $\textit{Kepler}$ samples. MS2b stars are tidally locked binaries with periods of days. G1/3 stars are heavily spotted, tidally locked RS CVn with periods of tens of days. G2 stars are less luminous, heavily spotted, tidally locked sub-subgiants with periods of $\sim10$ days. G4s stars have intermediate luminosities to G1/3 and G2, slow rotation periods (approaching 100 days) and are almost certainly all merger remnants. G4b stars have similar rotation periods and luminosities to G4s, but consist of sub-synchronously rotating binaries. We see no difference in indicators for the presence of very wide binary companions between any of these groups and control samples of photometric twin stars built for each group., Comment: 15 pages, 11 figures, 5 tables, submitted to MNRAS

The All-Sky Automated Survey for Supernovae (ASAS-SN) began observing in late-2011 and has been imaging the entire sky with nightly cadence since late 2017. A core goal of ASAS-SN is to release as much useful data as possible to the community. Working towards this goal, in 2017 the first ASAS-SN Sky Patrol was established as a tool for the community to obtain light curves from our data with no preselection of targets. Then, in 2020 we released static V-band photometry from 2013--2018 for 61 million sources. Here we describe the next generation ASAS-SN Sky Patrol, Version 2.0, which represents a major progression of this effort. Sky Patrol 2.0 provides continuously updated light curves for 111 million targets derived from numerous external catalogs of stars, galaxies, and solar system objects. We are generally able to serve photometry data within an hour of observation. Moreover, with a novel database architecture, the catalogs and light curves can be queried at unparalleled speed, returning thousands of light curves within seconds. Light curves can be accessed through a web interface (http://asas-sn.ifa.hawaii.edu/skypatrol/) or a Python client (https://asas-sn.ifa.hawaii.edu/documentation). The Python client can be used to retrieve up to 1 million light curves, generally limited only by bandwidth. This paper gives an updated overview of our survey, introduces the new Sky Patrol, and describes its system architecture. These results provide significant new capabilities to the community for pursuing multi-messenger and time-domain astronomy., Comment: Light curves can be accessed through a web interface http://asas-sn.ifa.hawaii.edu/skypatrol, or a Python client at http://asas-sn.ifa.hawaii.edu/documentation

We analyze the late time evolution of 12 supernovae (SNe) occurring over the last ${\sim}$41 years, including nine Type IIP/L, two IIb, and one Ib/c, using UBVR optical data from the Large Binocular Telescope (LBT) and difference imaging. We see late time (5 to 42 years) emission from nine of the eleven Type II SNe (eight Type IIP/L, one IIb). We consider radioactive decay, circumstellar medium (CSM) interactions, pulsar/engine driven emission, dust echoes, and shock perturbed binary companions as possible sources of emission. The observed emission is most naturally explained as CSM interactions with the normal stellar winds of red supergiants with mass loss rates in the range $-7.9\lesssim \log_{10}(M_\odot\text{yr}{}^{-1}) \lesssim-4.8$. We also place constraints on the presence of any shock heated binary companion to the Type Ib/c SN 2012fh and provide progenitor photometry for the Type IIb SN 2011dh, the only one of the six SNe with pre-explosion LBT observations where the SN has faded sufficiently to allow the measurement. The results are consistent with measurements from pre-explosion Hubble Space Telescope (HST) images., Comment: 22 pages, 14 figures, 6 tables, submitting to MNRAS

Masses and radii of stars can be derived by combining eclipsing binary light curves with spectroscopic orbits. In our previous work, we modeled the All-Sky Automated Survey for Supernovae (ASAS-SN) light curves of more than 30,000 detached eclipsing binaries using PHOEBE. Here we combine our results with 128 double-lined spectroscopic orbits from Gaia Data Release 3. We visually inspect ASAS-SN light curves of double-lined spectroscopic binaries on the lower main sequence and the giant branch, adding 11 binaries to our sample. We find that only 50% of systems have Gaia periods and eccentricities consistent with the ASAS-SN values. We use emcee and PHOEBE to determine masses and radii for a total of 122 stars with median fractional uncertainties of 7.9% and 6.3%, respectively., Comment: 11 pages, 9 figures. Submitted to MNRAS. Data available online at https://asas-sn.osu.edu/binaries

In previous work we identified a population of 38 cool and luminous variable stars in the Magellanic Clouds and examined 11 in detail in order to classify them as either Thorne-\.Zytkow Objects (T\.ZOs, red supergiants with a neutron star cores) or super-AGB stars (the most massive stars that will not undergo core collapse). This population includes HV\,2112, a peculiar star previously considered in other works to be either a T\.ZO or high-mass AGB star. Here we continue this investigation, using the kinematic and radio environments and local star formation history of these stars to place constraints on the age of the progenitor systems and the presence of past supernovae. These stars are not associated with regions of recent star formation, and we find no evidence of past supernovae at their locations. Finally, we also assess the presence of heavy elements and lithium in their spectra compared to red supergiants. We find strong absorption in Li and s-process elements compared to RSGs in most of the sample, consistent with super-AGB nucleosynthesis, while HV\,2112 shows additional strong lines associated with T\.ZO nucleosynthesis. Coupled with our previous mass estimates, the results are consistent with the stars being massive (~4-6.5M$_{\odot}$) or super-AGB (~6.5-12M$_{\odot}$) stars in the thermally pulsing phase, providing crucial observations of the transition between low- and high-mass stellar populations. HV\,2112 is more ambiguous; it could either be a maximally massive sAGB star, or a T\.ZO if the minimum mass for stability extends down to <13 M$_\odot$., Comment: 32 pages, 10 figures, 7 tables, spectroscopic data available at https://zenodo.org/record/7058608, accepted to The Astrophysical Journal

NGC 5273 is a known optical and X-ray variable AGN. We analyze new and archival IR, optical, UV, and X-ray data in order to characterize its long-term variability from 2000 to 2022. At least one optical changing-look event occurred between 2011 and 2014, when the AGN changed from a Type 1.8/1.9 Seyfert to a Type 1. It then faded considerably at all wavelengths, followed by a dramatic but slow increase in UV/optical brightness between 2021 and 2022. Near-IR (NIR) spectra in 2022 show prominent broad Paschen lines that are absent in an archival spectrum from 2010, making NGC 5273 one of the few AGNs to be observed changing-look in the NIR. We propose that NGC 5273 underwent multiple changing-look events between 2000 and 2022 -- starting as a Type 1.8/1.9, NGC 5273 changes-look to a Type 1 temporarily in 2002 and again in 2014, reverting back to a Type 1.8/1.9 by 2005 and 2017, respectively. In 2022, it is again a Type 1 Seyfert. We characterize the changing-look events and their connection to the dynamic accretion and radiative processes in NGC 5273, and propose that the variable luminosity (and thus, Eddington ratio) of the source is changing how the broad line region (BLR) reprocesses the continuum emission., Comment: 19 pages, 13 figures, 5 tables, accepted to MNRAS

Using blazar light curves from the optical All-Sky Automated Survey for Supernovae (ASAS-SN) and the $\gamma$-ray \textit{Fermi}-LAT telescope, we performed the most extensive statistical correlation study between both bands, using a sample of 1,180 blazars. This is almost an order of magnitude larger than other recent studies. Blazars represent more than 98\% of the AGNs detected by \textit{Fermi}-LAT and are the brightest $\gamma$-ray sources in the extragalactic sky. They are essential for studying the physical properties of astrophysical jets from central black holes. However, their $\gamma$-ray flare mechanism is not fully understood. Multi-wavelength correlations help constrain the dominant mechanisms of blazar variability. We search for temporal relationships between optical and $\gamma$-ray bands. Using a Bayesian Block Decomposition, we detect 1414 optical and 510 $\gamma$-ray flares, we find a strong correlation between both bands. Among all the flares, we find 321 correlated flares from 133 blazars, and derive an average rest-frame time delay of only 1.1$_{-8.5}^{+7.1}$ days, with no difference between the flat-spectrum radio quasars, BL Lacertae-like objects or low, intermediate, and high-synchrotron peaked blazar classes. Our time-delay limit rules out the hadronic proton-synchrotron model as the driver for non-orphan flares and suggests a leptonic single-zone model. Limiting our search to well-defined light curves and removing 976 potential but unclear ``orphan'' flares, we find 191 (13\%) and 115 (22\%) clear ``orphan'' optical and $\gamma$-ray flares. The presence of ``orphan'' flares in both bands challenges the standard one-zone blazar flare leptonic model and suggests multi-zone synchrotron sites or a hadronic model for some blazars., Comment: 30 pages (16 of appendix), 7 figures, 2 tables, Accepted for publication in MNRAS

We catalog the 443 bright supernovae discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) in $2018-2020$ along with the 519 supernovae recovered by ASAS-SN and 516 additional $m_{peak}\leq18$ mag supernovae missed by ASAS-SN. Our statistical analysis focuses primarily on the 984 supernovae discovered or recovered in ASAS-SN $g$-band observations. The complete sample of 2427 ASAS-SN supernovae includes earlier $V$-band samples and unrecovered supernovae. For each supernova, we identify the host galaxy, its UV to mid-IR photometry, and the offset of the supernova from the center of the host. Updated light curves, redshifts, classifications, and host galaxy identifications supersede earlier results. With the increase of the limiting magnitude to $g\leq18$ mag, the ASAS-SN sample is roughly complete up to $m_{peak}=16.7$ mag and is $90\%$ complete for $m_{peak}\leq17.0$ mag. This is an increase from the $V$-band sample where it was roughly complete up to $m_{peak}=16.2$ mag and $70\%$ complete for $m_{peak}\leq17.0$ mag., Comment: 14 pages, 7 figures, 4 tables. Updated to reflect changes made in the published version. Tables containing the catalog data presented in this submission are included in machine-readable format as ancillary files

Detached eclipsing binaries are the primary tool used to measure precise masses and radii of stars. In our previous paper estimating the parameters of more than 30,000 detached eclipsing binaries, we identified 766 eclipsing binaries with additional features in their All-Sky Automated Survey for Supernovae (ASAS-SN) and Transiting Exoplanet Survey Satellite (TESS) light curves. Here, we characterize these "extra-physics" systems, identifying eclipsing binaries with spotted stars, pulsating components, and candidate triple/quadruple systems. We use the Gaia, ATLAS, ZTF, and ASAS-SN variable star catalogs to consider possible blends. We use MIST isochrones and evolutionary tracks to identify systems with main sequence, subgiant, and giant primaries and highlight systems in sparsely populated regions of the color-magnitude diagram. We find that the orbital period distribution of spotted binaries is divided by evolutionary state and find 68 with X-ray detections. For the candidate triple/quadruples and pulsating systems, we calculate the extra orbital/pulsational period and identify systems with resonances. Finally, we highlight a number of exotic systems, including eclipsing CVs, subdwarfs, and binaries with disks., Comment: 19 pages, 14 figures. Submitted to MNRAS

The correlation between the broad line region radius and continuum luminosity ($R-L$ relation) of active galactic nuclei (AGN) is critical for single-epoch mass estimates of supermassive black holes (SMBHs). At $z \sim 1-2$, where AGN activity peaks, the $R-L$ relation is constrained by the reverberation mapping (RM) lags of the Mg II line. We present 25 Mg II lags from the Australian Dark Energy Survey (OzDES) RM project based on six years of monitoring. We define quantitative criteria to select good lag measurements and verify their reliability with simulations based on both the damped random walk stochastic model and the re-scaled, re-sampled versions of the observed lightcurves of local, well-measured AGN. Our sample significantly increases the number of Mg II lags and extends the $R-L$ relation to higher redshifts and luminosities. The relative iron line strength $\mathcal{R}_{\rm Fe}$ has little impact on the $R-L$ relation. The best-fit Mg II $R-L$ relation has a slope $\alpha = 0.39 \pm 0.08$ with an intrinsic scatter $\sigma_{\rm rl} = 0.15^{+0.03}_{-0.02}$. The slope is consistent with previous measurements and shallower than the H$\beta$ $R-L$ relation. The intrinsic scatter of the new $R-L$ relation is substantially smaller than previous studies and comparable to the intrinsic scatter of the H$\beta$ $R-L$ relation. Our new $R-L$ relation will enable more precise single-epoch mass estimates and SMBH demographic studies at cosmic noon., Comment: 16 pages, 8 figures; MNRAS, Volume 522, pp.4132

Gaia DR3 provides >181, 000 radial velocity solutions for single-lined spectroscopic binaries (SB1s) which can be used to search for non-interacting compact object+star binary candidates by selecting systems with large mass functions. We selected 234 such systems and identified 114 systems with good RV solutions in DR3. We used light curves from ASAS-SN and TESS to identify and remove 31 eclipsing binaries to produce a catalog of 80 compact object+star candidates, including 38 ellipsoidal variables. The positions of these candidates on Gaia and 2MASS CMDs suggest that many of these systems are binaries with luminous companions. We compared the periods and eccentricities of detached eclipsing binaries in Gaia DR3 and ASAS-SN, and found that ~11% and ~60% of the binaries had different periods and eccentricities. We also compared RV solutions for 311 binaries in both Gaia DR3 and the Ninth Catalog of Spectroscopic Binary Orbits (SB9), and found similar results. We do not identify any strong candidates for non-interacting compact object+star binaries., Comment: 15 pages, 10 figures. Submitted to MNRAS

We present the first estimate of the Galactic nova rate based on optical transient surveys covering the entire sky. Using data from the All-Sky Automated Survey for Supernovae (ASAS-SN) and \textit{Gaia} -- the only two all-sky surveys to report classical nova candidates -- we find 39 confirmed Galactic novae and 7 additional unconfirmed candidates discovered from 2019--2021, yielding a nova discovery rate of $\approx 14$ yr$^{-1}$. Using accurate Galactic stellar mass models, three-dimensional dust maps, and incorporating realistic nova light curves, we have built a sophisticated Galactic nova model that allows an estimate of the recovery fraction of Galactic novae from these surveys over this time period. The observing capabilities of each survey are distinct: the high cadence of ASAS-SN makes it sensitive to fast novae, while the broad observing filter and high spatial resolution of \textit{Gaia} make it more sensitive to highly reddened novae across the entire Galactic plane and bulge. Despite these differences, we find that ASAS-SN and \textit{Gaia} give consistent Galactic nova rates, with a final joint nova rate of $26 \pm 5$ yr$^{-1}$. This inferred nova rate is substantially lower than found by many other recent studies. Critically assessing the systematic uncertainties in the Galactic nova rate, we argue that the role of faint fast-fading novae has likely been overestimated, but that subtle details in the operation of transient alert pipelines can have large, sometimes unappreciated effects on transient recovery efficiency. Our predicted nova rate can be directly tested with forthcoming red/near-infrared transient surveys in the southern hemisphere., Comment: 24 pages, 9 figures

We searched for and found no higher mass (>3Msun) unbound binary stellar companions to the progenitor of pulsar J1124-5916. There are lower mass candidates, but they all have high probabilities of being false positives. There are no candidates for it now being a fully unbound triple system. Even if one of the lower mass candidates is an unbound companion, it seems unlikely that it could have contributed to stripping the progenitor prior to the supernova. The stars are too low mass to be significant mass gainers, and they are too slowly moving to be the survivors of a compact, post-common envelope binary. The addition of one more system slightly improves the statistical constraints on the binary and triple status of supernova progenitors just before and after death., Comment: submitted to MNRAS

Large scale surface convection on red supergiants (RSGs) can lead to shifts in the photocenter of the star which might be measured by Gaia and used as a new probe of the surface dynamics of these rare but important stars. Unlike brightness variations, photocenter motions would provide information on the physical scale of the convective cells. The signal would be that RSGs show an excess astrometric noise at the level of a few percent of the stellar radius. Unfortunately, we find that the excess astrometric noise level of Gaia EDR3 is roughly an order of magnitude too large to detect the predicted motions and that RSGs have excess astrometric noise indistinguishable from other stars of similar magnitude and parallax. The typical excess astrometric noise steadily decreases with G magnitude (for G<11 mag), so it is crucial to compare stars of similar brightness., Comment: 5 pages, submitted to MNRAS

We have built a new model for the lens system SDSS J1004+4112 including the recently measured time delay of the fourth quasar image. This time delay has a strong influence on the inner mass distribution of the lensing cluster ($\rho \propto r^{-\alpha}$) allowing us to determine $\alpha=1.18^{+0.02(+0.11)}_{-0.03(-0.18)}$ at the 68% (95%) confidence level in agreement with hydrodynamical simulations of massive galaxy clusters. We find an offset between the brightest cluster galaxy (BCG) and the dark matter halo of $3.8^{+0.6(+1.4)}_{-0.7(-1.3)}$ kpc at 68% (95%) confidence which is compatible with other galaxy cluster measurements. As an observational challenge, the estimated time delay between the leading image C and the faint (I=24.7) fifth image E is roughly 8 yr., Comment: 9 pages, 3 figures, 4 tables. ApJ in press

We present new light curves for the four bright images of the five image cluster-lensed quasar gravitational lens system SDSS~J1004+4112. The light curves span 14.5 yr and allow measurement of the time delay between the trailing bright quasar image D and the leading image C. When we fit all four light curves simultaneously and combine the models using the Bayes information criterion, we find a time delay of $\Delta t_{DC}= 2458.47 \pm 1.02$ days (6.73 yr), the longest ever measured for a gravitational lens. For the other two independent time delays we obtain $\Delta t_{BC}=782.20 \pm 0.43$ days (2.14 yr) and $\Delta t_{AC}= 825.23 \pm 0.46$ days (2.26 yr), in agreement with previous results. The information criterion is needed to weight the results for light curve models with different polynomial orders for the intrinsic variability and the effects of differential microlensing. The results using the Akaike information criterion are slightly different, but, in practice, the absolute delay errors are all dominated by the $\sim 4\%$ cosmic variance in the delays rather than the statistical or systematic measurement uncertainties. Despite the lens being a cluster, the quasar images show slow differential variability due to microlensing at the level of a few tenths of a magnitude., Comment: 12 pages, 5 figures. ApJ in press

Detached eclipsing binaries are a fundamental tool for measuring the physical parameters of stars that are effectively evolving in isolation. Starting from more than 40,000 eclipsing binary candidates identified by the All-Sky Automated Survey for Supernovae (ASAS-SN), we use PHOEBE to determine the sum of the fractional radii, the ratio of effective temperatures, the inclinations, and the eccentricities for 35,464 systems. We visually inspect all the light curve models to verify the model fits and examine the TESS light curves, when available, to select systems with evidence for additional physics, such as spots, mass transfer, and hierarchical triples. We examine the distributions of the eclipsing binary model parameters and the orbital parameters. We identify two groups in the sum of the fractional radii and effective temperature ratio parameter space that may distinguish systems approaching the semidetached limit. Combining Gaia EDR3 with extinction estimates from 3-dimensional dust maps, we examine the properties of the systems as a function of their absolute magnitude and evolutionary state. Finally, we present light curves of selected eclipsing binaries that may be of interest for follow-up studies., Comment: 24 pages, 26 figures. Submitted to MNRAS

AT2019pev is a nuclear transient in a narrow-line Seyfert 1 galaxy at $z=0.096$. The archival ultraviolet, optical and infrared data showed features of both tidal disruption events (TDEs) and active galactic nuclei (AGNs), and its nature is not fully understood. We present detailed X-ray observations of AT2019pev taken with Swift, Chandra and NICER over 173 days of its evolution since the first Swift XRT epoch. The X-ray luminosity increases by a factor of five in five days from the first Swift XRT epoch to the lightcurve peak. The lightcurve decays by a factor of ten over $\sim$75 days and then flattens with a weak re-brightening trend at late times. The X-ray spectra show a "harder-when-brighter" trend before peak and a "harder-when-fainter" trend after peak, which may indicate a transition of accretion states. The archival ground-based optical observations show similar time evolution as the X-ray lightcurves. Beyond the seasonal limit of the ground-based observations, the Gaia lightcurve is rising toward an equally bright or brighter peak 223 days after the optical discovery. Combining our X-ray analysis and archival multi-wavelength data, AT2019pev more closely resembles an AGN transient., Comment: 14 pages, 6 figures; submitted to MNRAS

The All-Sky Automated Survey for Supernovae (ASAS-SN) is the first optical survey to monitor the entire sky, currently with a cadence of $\lesssim 24$ hours down to $g \lesssim 18.5$ mag. ASAS-SN has routinely operated since 2013, collecting $\sim$ 2,000 to over 7,500 epochs of $V$ and $g-$band observations per field to date. This work illustrates the first analysis of ASAS-SN's newer, deeper, higher cadence $g-$band data. From an input source list of ${\sim}55$ million isolated sources with $g<18$~mag, we identified $1.5\times10^6$ variable star candidates using a random forest classifier trained on features derived from $\textit{Gaia}$, 2MASS, and AllWISE. Using ASAS-SN $g-$band light curves, and an updated random forest classifier augmented with data from Citizen ASAS-SN, we classified the candidate variables into 8 broad variability types. We present a catalog of ${\sim}116,000$ new variable stars with high classification probabilities, including ${\sim}111,000$ periodic variables and ${\sim}5,000$ irregular variables. We also recovered ${\sim}263,000$ known variable stars., Comment: 18 pages, 21 figures, 1 table. Submitted to MNRAS. The g-band catalog of variables and their light curves are available here: https://drive.google.com/drive/folders/1gxcIokRsw1eyPmbPZ0-C8blfRGItSOAu

We report the discovery of a stripped giant + lower giant binary, 2M04123153+6738486 (2M0412), identified during a search for non-interacting compact object-star binaries. 2M0412 is an evolved ($T_{\rm eff, giant}\simeq4000$ K), luminous ($L_{\rm giant}\simeq150~L_\odot$) red giant in a circular $P=81.2$ day binary. 2M0412 is a known variable star previously classified as a semi-regular variable. The cross-correlation functions of follow-up Keck/HIRES and LBT/PEPSI spectra show an RV-variable second component with implied mass ratio $q=M_{\rm giant}/M_{\rm comp}\simeq0.20\pm0.01$. The ASAS-SN, ATLAS, TESS and ZTF light curves show that the giant is a Roche lobe filling ellipsoidal variable with an inclination of $49.4^\circ{}\pm{0.3^{\circ}}$, and a giant mass of $M_{\rm giant}=0.38\pm0.01~ M_\odot$ for a distance of $\simeq3.7$ kpc. The mass of the giant indicates that its envelope has been stripped. The giant companion on the lower red giant branch has a mass of $M_{\rm comp}=1.91\pm0.03~M_\odot$ with $T_{\rm eff, comp}\simeq5000$ K, $L_{\rm comp}\simeq60~L_\odot$ and $R_{\rm comp}\simeq11~R_\odot$. We also identify an orbital phase dependent, broad $\rm H\alpha$ emission line which could indicate ongoing accretion from the stripped red giant onto the companion., Comment: Revised version of the paper following comments from the referee, submitted to MNRAS. arXiv admin note: text overlap with arXiv:2101.02212

We introduce a new model for understanding AGN continuum variability. We start from a Shakura--Sunyaev thin accretion disc with a steady-state radial temperature profile $T(R)$ and assume that the variable flux is due to axisymmetric temperature perturbations $\delta T(R,t)$. After linearizing the equations, we fit UV-optical AGN lightcurves to determine $\delta T(R,t)$ for a sample of seven AGNs. We see a diversity of $|\delta T/T| \sim 0.1$ fluctuation patterns which are not dominated by outgoing waves traveling at the speed of light as expected for the "lamppost" model used to interpret disc reverberation mapping studies. Rather, the most common pattern resembles slow ($v \ll c$) ingoing waves. An explanation for our findings is that these ingoing waves trigger central temperature fluctuations that act as a lamppost, producing lower amplitude temperature fluctuations moving outwards at the speed of light. The lightcurves are dominated by the lamppost signal -- even though the temperature fluctuations are dominated by other structures with similar variability time-scales -- because the discs exponentially smooth the contributions from the slower moving ($v \ll c$) fluctuations to the observed lightcurves. This leads to lightcurves that closely resemble the expectations for a lamppost model but with the slow variability time-scales of the ingoing waves. This also implies that longer time-scale variability signals will increasingly diverge from lamppost models because the smoothing of slower-moving waves steadily decreases as their period or spatial wavelength increases., Comment: 18 pages, 25 figures. Published by MNRAS. Animated versions of select figures (see Section 8) can be found at https://github.com/jackneustadt/disc-gifs

Using data from the Complete Nearby ($z_{host}<0.02$) sample of Type Ia Supernovae (CNIa0.02), we discover a linear relation between two parameters derived from the $B-V$ color curves of Type Ia supernovae: the "color stretch" $s_{BV}$ and the rising color slope $s_0^*(B-V)$ after the peak, and this relation applies to the full range of $s_{BV}$. The $s_{BV}$ parameter is known to be tightly correlated with the peak luminosity, and especially for "fast decliners" (dim Type Ia supernovae), and the luminosity correlation with $s_{BV}$ is markedly better than with the classic light-curve width parameters such as $\Delta{m_{15}(B)}$. Thus our new linear relation can be used to infer peak luminosity from $s_0^*$. Unlike $s_{BV}$ (or $\Delta{m_{15}}$), the measurement of $s_0^*(B-V)$ does not rely on the well-determined time of light-curve peak or color maximum, making it less demanding on the light-curve coverage than past approaches., Comment: Submitted to AAS Journals, 7 pages, 4 figures

We present the first results from Citizen ASAS-SN, a citizen science project for the All-Sky Automated Survey for Supernovae (ASAS-SN) hosted on the Zooniverse platform. Citizen ASAS-SN utilizes the newer, deeper, higher cadence ASAS-SN $g$-band data and tasks volunteers to classify periodic variable star candidates based on their phased light curves. We started from 40,640 new variable candidates from an input list of ${\sim} 7.4$ million stars with $\delta < -60^\circ$ and the volunteers identified 10,420 new discoveries which they classified as 4,234 pulsating variables, 3,132 rotational variables, 2,923 eclipsing binaries, and 131 variables flagged as Unknown. They classified known variable stars with an accuracy of 89% for pulsating variables, 81% for eclipsing binaries, and 49% for rotational variables. We examine user performance, agreement between users, and compare the citizen science classifications with our machine learning classifier updated for the $g$-band light curves. In general, user activity correlates with higher classification accuracy and higher user agreement. We used the user's "Junk" classifications to develop an effective machine learning classifier to separate real from false variables, and there is a clear path for using this "Junk" training set to significantly improve our primary machine learning classifier. We also illustrate the value of Citizen ASAS-SN for identifying unusual variables with several examples., Comment: 19 pages, 20 figures, 4 tables. Submitted to MNRAS. The DR1 catalog and light curves are available here: https://drive.google.com/drive/folders/1sLyJuOTAdEfccSOVkBIhb9YlK6JfOFXl?usp=sharing

We analyze new multi-filter Hubble Space Telescope (HST) photometry of the normal Type Ia supernova (SN Ia) 2011fe out to $\approx 2400~$days after maximum light, the latest observations to-date of a SN Ia. We model the pseudo-bolometric light curve with a simple radioactive decay model and find energy input from both $^{57}$Co and $^{55}$Fe are needed to power the late-time luminosity. This is the first detection of $^{55}$Fe in a SN Ia. We consider potential sources of contamination such as a surviving companion star or delaying the deposition timescale for $^{56}$Co positrons but these scenarios are ultimately disfavored. The relative isotopic abundances place direct constraints on the burning conditions experienced by the white dwarf (WD). Additionally, we place a conservative upper limit of $< 10^{-3}~M_\odot$ on the synthesized mass of $^{44}$Ti. Only 2 classes of explosion models are currently consistent with all observations of SN2011fe: 1) the delayed detonation of a low-$\rho_c$, near-$\rm{M}_{\rm{Ch}}$ ($1.2-1.3~M_\odot$) WD, or 2) a sub-$\rm{M}_{\rm{Ch}}$ ($1.0-1.1~M_\odot$) WD experiencing a thin-shell double detonation., Comment: 14 pages, 8 figures, 1 table. MNRAS, accepted

We present three new spectra of the nearby Type Ia supernova (SN Ia) 2011fe covering $\approx 480-850~$days after maximum light and show that the ejecta undergoes a rapid ionization shift at $\sim 500~$days after explosion. The prominent [FeIII] emission lines at $\approx 4600~$\r{A} are replaced with the permitted FeI+FeII blends at $\sim 4400~$\r{A} and $\sim 5400~$\r{A}. The $\approx 7300~$\r{A} feature, which is produced by [FeII]+[NiII] at $\lesssim 400~$days after explosion, is replaced by broad ($\approx \pm 15\,000~\rm{km}~\rm{s}^{-1}$) symmetric [CaII] emission. Models predict this ionization transition occurring $\sim 100$ days later than what is observed, which we attribute to clumping in the ejecta. Finally, we use the nebular-phase spectra to test several proposed progenitor scenarios for SN2011fe. Non-detections of H and He exclude nearby non-degenerate companions, [OI] non-detections disfavor the violent merger of two white dwarfs, and the symmetric emission-line profiles favor a symmetric explosion., Comment: 8 pages, 1 table, 6 figures. Accepted by ApJL

With Gaia parallaxes it is possible to study the stellar populations associated with individual Galactic supernova remnants (SNR) to estimate the mass of the exploding star. Here we analyze the luminous stars near the Vela pulsar and SNR to find that its progenitor was probably (>90%) low mass (8.1-10.3Msun). The presence of the O star gamma2 Vel a little over 100 pc from Vela is the primary ambiguity, as including it in the analysis volume significantly increases the probability (to 5%) of higher mass (>20Msun) progenitors. However, to be a high mass star associated with gamma2 Vel's star cluster at birth, the progenitor would have to a runaway star from an unbound binary with an unusually high velocity. The primary impediment to analyzing large numbers of Galactic SNRs in this manner is the lack of accurate distances. This can likely be solved by searching for absorption lines from the SNR in stars as a function of distance, a method which yielded a distance to Vela in agreement with the direct pulsar parallax. If Vela was a 10Msun supernova in an external galaxy, the 50 pc search region used in extragalactic studies would contain only ~10% of the stars formed in a 50~pc region around the progenitor at birth and ~90% of the stars in the search region would have been elsewhere., Comment: submitted to MNRAS

As part of an All-Sky Automated Survey for SuperNovae (ASAS-SN) search for sources with large flux decrements, we discovered a transient where the quiescent, stellar source, ASASSN-V J192114.84+624950.8, rapidly decreased in flux by $\sim55\%$ ($\sim0.9$ mag) in the g-band. The \textit{TESS} light curve revealed that the source is a highly eccentric, eclipsing binary. Fits to the light curve using \textsc{phoebe} find the binary orbit to have $e=0.79$, $P_{\rm orb}=18.462~\text{days}$, and $i=88.6^{\circ}$ and the ratios of the stellar radii and temperatures to be $R_2/R_1 = 0.71$ and $T_{e,2}/T_{e,1} = 0.82$. Both stars are chromospherically active, allowing us to determine their rotational periods of $P_1=1.52$ days and $P_2=1.79$ days, respectively. A LBT/MODS spectrum shows that the primary is a late-G or early-K type dwarf. Fits to the SED show that the luminosities and temperatures of the two stars are $L_1 = 0.48~L_{\sun}$, $T_1= 5050~K$, $L_2 = 0.12~L_{\sun}$, and $T_{2} = 4190~K$. We conclude that ASASSN-V J192114.84+624950.8 consists of two chromospherically active, rotational variable stars in a highly elliptical eclipsing orbit., Comment: 9 pages, 9 figures, submitted to MNRAS

We report on the search for electromagnetic counterparts to the nine gravitational-wave events with a $>$60\% probability of containing a neutron star during the third (O3) LIGO-Virgo Collaboration (LVC) observing run with the All-Sky Automated Survey for SuperNovae (ASAS-SN). No optical counterparts associated with a gravitational wave event was found. However, thanks to its network of telescopes, the average area visible to at least one ASAS-SN site during the first 10 hours after the trigger contained $\sim$30\% of the integrated source location probability. Through a combination of normal operations and target-of-opportunity observations, ASAS-SN observations of the highest probability fields began within one hour of the trigger for four of the events. After 24 hours, ASAS-SN observed $>$60\% of total probability for three events and $>$40\% for all but one of the events. This is the largest area coverage to a depth of $g = 18.5$ mag from any survey with published coverage statistics for seven of the nine events. With its observing strategy, five sites around the world, and a large field of view, ASAS-SN will be one of the leading surveys to optically search for nearby neutron star mergers during LVC O4., Comment: 11 pages, 16 figures, submitted to MNRAS for publication, comments are welcome

The fraction of stars which are in binaries or triples at the time of stellar death and the fraction of these systems which survive the supernova (SN) explosion are crucial constraints for evolution models and predictions for gravitational wave source populations. These fractions are also subject to direct observational determination. Here we search 10 supernova remnants (SNR) containing compact objects with proper motions for unbound binaries or triples using Gaia EDR3 and new statistical methods and tests for false positives. We confirm the one known example of an unbound binary, HD 37424 in G180.0-01.7, and find no other examples. Combining this with our previous searches for bound and unbound binaries, and assuming no bias in favor of finding interacting binaries, we find that 72.0% (52.2%-86.4%, 90% confidence) of SN producing neutron stars are not binaries at the time of explosion, 13.9% (5.4%-27.2%) produce bound binaries and 12.5% (2.8%-31.3%) produce unbound binaries. With a strong bias in favor of finding interacting binaries, the medians shift to 76.0% were not binaries at death, 9.5% leave bound and 13.2% leave unbound binaries. Of explosions that do not leave binaries, <18.9% can be fully unbound triples. These limits are conservatively for M>5Msun stars, although the mass limits for individual systems are significantly stronger. At birth, the progenitor of PSR J0538+2817 was probably a 13-19Msun star, and at the time of explosion it was probably a Roche limited, partially stripped star transferring mass to HD 37424 and then producing a Type IIL or IIb supernova., Comment: submitted to MNRAS

We present $V$-band photometry of the 20,000 brightest asteroids using data from the All-Sky Automated Survey for Supernovae (ASAS-SN) between 2012 and 2018. We were able to apply the convex inversion method to more than 5,000 asteroids with more than 60 good measurements in order to derive their sidereal rotation periods, spin axis orientations, and shape models. We derive unique spin state and shape solutions for 760 asteroids, including 163 new determinations. This corresponds to a success rate of about 15%, which is significantly higher than the success rate previously achieved using photometry from surveys. We derive the first sidereal rotation periods for additional 69 asteroids. We find good agreement in spin periods and pole orientations for objects with prior solutions. We obtain a statistical sample of asteroid physical properties that is sufficient for the detection of several previously known trends, such as the underrepresentation of slow rotators in current databases, and the anisotropic distribution of spin orientations driven by the nongravitational forces. We also investigate the dependence of spin orientations on the rotation period. Since 2018, ASAS-SN has been observing the sky with higher cadence and deeper limiting magnitude, which will lead to many more new solutions in just a few years., Comment: Accepted for publication in Astronomy and Astrophysics

We use ASAS V-band and ASAS-SN g-band observations to model the long-period detached eclipsing binary ASASSN-21co. ASAS observations show an eclipse of depth V ~ 0.6 mag in April of 2009. ASAS-SN g-band observations from March of 2021 show an eclipse of similar duration and depth, suggesting an orbital period of 11.9 years. We combine the g-band observations with additional BVRI photometry taken during the eclipse to model the eclipse using PHOEBE. We find that the system is best described by two M giants with a ratio of secondary radius to primary radius of ~0.61. Optical spectra taken during the eclipse are consistent with at least one component of the binary being an M giant, and we find no temporal changes in the spectral features. The eclipse itself is asymmetric, showing an increase in brightness near mid-eclipse, likely due to rotational variability that is too low amplitude to be observed out-of-eclipse., Comment: 4 pages, 1 figure, published in RNAAS

There is a longstanding discrepancy between the observed Galactic classical nova rate of $\sim 10$ yr$^{-1}$ and the predicted rate from Galactic models of $\sim 30$--50 yr$^{-1}$. One explanation for this discrepancy is that many novae are hidden by interstellar extinction, but the degree to which dust can obscure novae is poorly constrained. We use newly available all-sky three-dimensional dust maps to compare the brightness and spatial distribution of known novae to that predicted from relatively simple models in which novae trace Galactic stellar mass. We find that only half ($\sim 48$\%) of novae are expected to be easily detectable ($g \lesssim 15$) with current all-sky optical surveys such as the All-Sky Automated Survey for Supernovae (ASAS-SN). This fraction is much lower than previously estimated, showing that dust does substantially affect nova detection in the optical. By comparing complementary survey results from ASAS-SN, OGLE-IV, and the Palomar Gattini IR-survey in the context of our modeling, we find a tentative Galactic nova rate of $\sim 40$ yr$^{-1}$, though this could decrease to as low as $\sim 30$ yr$^{-1}$ depending on the assumed distribution of novae within the Galaxy. These preliminary estimates will be improved in future work through more sophisticated modeling of nova detection in ASAS-SN and other surveys., Comment: 15 pages, 9 figures

The majority of non-merging stellar mass black holes are discovered by observing high energy emission from accretion processes. Here we pursue the large, but still mostly unstudied population of non-interacting black holes and neutron stars by searching for the tidally-induced ellipsoidal variability of their stellar companions. We start from a sample of about 200,000 rotational variables, semi-regular variables, and eclipsing binary stars from the All-Sky Automated Survey for Supernovae (ASAS-SN). We use a $\chi^2$ ratio test followed by visual inspection to identify 369 candidates for ellipsoidal variability. We also discuss how to combine the amplitude of the variability with mass and radius estimates for observed stars to calculate a minimum companion mass, identifying the most promising candidates for high mass companions., Comment: 13 pages, 13 figures, 4 tables. Submitted to MNRAS

We characterize the extreme heartbeat star system MACHO 80.7443.1718 in the LMC using TESS photometry and spectroscopic observations from the Magellan Inamori Kyocera Echelle (MIKE) and SOAR Goodman spectographs. MACHO 80.7443.1718 was first identified as a heartbeat star system in the All-Sky Automated Survey for SuperNovae (ASAS-SN) with $P_{\rm orb}=32.836\pm0.008\,{\rm d}$. MACHO 80.7443.1718 is a young (${\sim}6$~Myr), massive binary, composed of a B0 Iae supergiant with $M_1 \simeq 35 M_\odot$ and an O9.5V secondary with $M_2 \simeq 16 M_\odot$ on an eccentric ($e=0.51\pm0.03$) orbit. In addition to having the largest variability amplitude amongst all known heartbeats stars, MACHO 80.7443.1718 is also one of the most massive heartbeat stars yet discovered. The B[e] supergiant has Balmer emission lines and permitted/forbidden metallic emission lines associated with a circumstellar disk. The disk rapidly dissipates at periastron which could indicate mass transfer to the secondary, but re-emerges immediately following periastron passage. MACHO 80.7443.1718 also shows tidally excited oscillations at the $N=25$ and $N=41$ orbital harmonics and has a rotational period of 4.4 d., Comment: 21 pages, 16 figures. Submitted to MNRAS

We present updated results of the Large Binocular Telescope Search for Failed Supernovae. This search monitors luminous stars in 27 nearby galaxies with a current baseline of 11~yr of data. We re-discover the failed supernova (SN) candidate N6946-BH1 as well as a new candidate, M101-OC1. M101-OC1 is a blue supergiant that rapidly disappears in optical wavelengths with no evidence for significant obscuration by warm dust. While we consider other options, a good explanation for the fading of M101-OC1 is a failed SN, but follow-up observations are needed to confirm this. Assuming only one clearly detected failed SN, we find a failed SN fraction $f = 0.16^{+0.23}_{-0.12}$ at 90 per~cent confidence. We also report on a collection of stars that show slow ($\sim$decade), large amplitude ($\Delta L/L > 3$) luminosity changes., Comment: 14 pages, 11 figures, 5 tables, 2 machine-readable tables (included as ancillary txt files)