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ABSTRACT We search a sample of 9361 613 isolated sources with 13<g<14.5 mag for slowly varying sources. We select sources with brightness changes larger than $$\sim 0.03$$ mag yr−1 over 10 yr, removing false positives due to, for example, nearby bright stars or high proper motions. After a thorough visual inspection, we find 782 slowly varying systems. Of these systems, 433 are identified as variables for the first time, 349 are previously classified as variables, and there are roughly equal numbers of sources becoming brighter and fainter. Previously classified systems were mostly identified as semiregular variables (SR), slow irregular variables (L), spotted stars (ROT), or unknown (MISC or VAR), as long time-scale variability does not fit into a standard class. The sources are scattered across the CMD and can be placed into five groups that exhibit distinct behaviours. The largest groups are very red subgiants and lower main sequence stars. There are also eight AGNs. There are 551 candidates ($$\sim$$ 70 per cent) that also show shorter time-scale periodic variability, mostly with periods longer than 10 d. The variability of 191 of these candidates may be related to dust. 

ABSTRACT 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 ($$\sim 0.75 \, {\rm M}_{\odot }$$ for lower main sequence primaries and $$\sim 0.9$$–$$1.2 \, {\rm M}_{\odot }$$ for RS CVn and sub-subgiants). Their companion mass range estimates allow companion masses down to $$M_2/M_1\simeq 0.1$$, although the main sequence population may have a higher minimum mass fraction ($$\sim 0.4$$). We see weak evidence of an inclination limit $$\gtrsim 50^{\circ }$$ 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. 

Abstract We use a multilevel perceptron (MLP) neural network to obtain photometry of saturated stars in the All-Sky Automated Survey for Supernovae (ASAS-SN). The MLP can obtain fairly unbiased photometry for stars fromg≃ 4 to 14 mag, particularly compared to the dispersion (15%–85% 1σrange around the median) of 0.12 mag for saturated (g< 11.5 mag) stars. More importantly, the light curve of a nonvariable saturated star has a median dispersion of only 0.037 mag. The MLP light curves are, in many cases, spectacularly better than those provided by the standard ASAS-SN pipelines. While the network was trained ong-band data from only one of ASAS-SN’s 20 cameras, initial experiments suggest that it can be used for any camera and the older ASAS-SNV-band data as well. The dominant problems seem to be associated with correctable issues in the ASAS-SN data reduction pipeline for saturated stars more than the MLP itself. The method is publicly available as a light-curve option on ASAS-SN Sky Patrol v1.0. 

ABSTRACT We report on spectroscopic and photometric observations of the AM Canum Venaticorum (AM CVn) system ASASSN-21br, which was discovered in outburst by the All-Sky Automated Survey for Supernovae in 2021 February. The outburst lasted for around three weeks, and exhibited a pronounced brightness dip for $$\approx$$4 d, 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 min, 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. 

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. 

Light echoes occur when light from a luminous transient is scattered by dust back into our line of sight with a time delay due to the extra propagation distance. We introduce a novel approach to estimating the distance to a source by combining light echoes with recent three-dimensional dust maps. We identify light echoes from the historical supernovae Cassiopeia A and SN 1572 (Tycho) in nearly a decade of imaging from the All-Sky Automated Survey for Supernovae (ASAS-SN). Using these light echoes, we find distances of $3.6\pm 0.1$kpc and ${3.2}_{-0.2}^{+0.1}$kpc to Cas A and Tycho, respectively, which are generally consistent with previous estimates but are more precise. These distance uncertainties are primarily dominated by the low distance resolution of the 3D dust maps, which will likely improve in the future. The candidate single degenerate explosion donor stars B and G in Tycho are clearly foreground stars. Finally, the inferred reddening towards each SN agrees well with the intervening column density estimates from X-ray analyses of the remnants.