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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 investigate the progenitor of the Crab supernova by examining the remnant’s surrounding stellar population. The Crab is interesting because of the apparently low energy and mass of the supernova remnant. We also know it was not a binary at death and that the explosion formed a neutron star. Using Gaia EDR3 parallaxes and photometry, we analyse stars inside a cylinder with a projected radius of 100 pc and spanning distances from $$\sim 1600$$ to 2300 pc set by the $$2\sigma$$ uncertainties in the Crab’s parallax. We also individually model the most luminous stars local to the Crab. The two most luminous stars are blue, roughly main sequence stars with masses of $$\sim 11\, {\rm M}_{\odot }$$. We estimate the stellar population’s age distribution using solar metallicity PARSEC isochrones. The estimated age distribution of the 205 $$M_{\mathrm{ G}} < 0$$ stars modestly favour lower mass stars, consistent with an AGB star or a lower mass binary merger as the progenitor, but statistically we cannot rule out higher masses. This may be driven by contamination due to the $$\sim 700$$ pc span of the cylinder in distance. 

Abstract 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, multifiber echelle spectroscopy, it is now possible to obtain accurate distances to many SNRs with limited extinction by searching for the appearance of high-velocity Caiior Naiabsorption 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 (1.30–1.47 kpc at 90% confidence), which is consistent with the median parallax distance to the pulsar of 1.46 kpc (1.12–2.10 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, HD 37424 at a photogeometric distance of 1.45 kpc (1.40–1.50 kpc at 1σ). The presence of high-velocity absorption lines is correlated with the Hα/O [iii] emission-line flux of the SNR but not with the radio flux. 

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. 

ABSTRACT Masses and radii of stars can be derived by combining eclipsing binary light curves with spectroscopic orbits. In our previous work, we modelled 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 also visually inspect ASAS-SN light curves of the Gaia double-lined spectroscopic binaries on the lower main sequence and the giant branch, adding 11 binaries to our sample. We find that only 50 per cent 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 per cent and 6.3 per cent, respectively.