Multiperiodic Galactic field RR Lyrae stars in the ASAS catalog

The All Sky Automated Survey (ASAS) monitors bright stars (8 mag < V < 14 mag) south of declination +28 deg. The ASAS Catalogue of Variable Stars (ACVS) presently contains 50,099 objects; among them are 2212 objects classified as RR Lyrae pulsating variables. We use ASAS photometric V band data to search for multiperiodicity in those stars. We find that 73 of 1435 RRab stars and 49 of 756 RRc stars exhibit the Blazhko effect. We observe a deficiency of RRab Blazhko variables with main pulsation periods greater than 0.65 days. The Blazhko periods of RRc stars exhibit a strongly bimodal distribution. During our study we discovered the Blazhko effect with multiple periods in object ASAS 050747-3351.9 = SU Col. Blazhko periods of 89.3 d and 65.8 d and a candidate of 29.5 d were identified with periodogram peaks near the first three harmonics of the main pulsation. These observations may inspire new models of the Blazhko effect, which has eluded a consistent theory since its discovery about one hundred years ago. Long term lightcurve changes were found in 29 stars. We also found 19 Galactic double mode pulsators (RRd), of which 4 are new discoveries, raising the number of ASAS discoveries of such objects to 16, out of 27 known in the field of our Galaxy.Comment: 12 pages, 10 figures, published in MNRA

Pre-discovery and Follow-up Observations of the Nearby SN 2009nr: Implications for Prompt Type Ia SNe

We present photometric and spectroscopic observations of the Type Ia supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery announcement at what turned out to be ten days after peak, we detected it at V ~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North telescope 2 weeks prior to the peak, and then followed it up with telescopes ranging in aperture from 10-cm to 6.5-m. Using early photometric data available only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN 1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95 mag. The early post-maximum spectra closely resemble those of SN 1991T, while the late time spectra are more similar to those of normal Type Ia SNe. Interestingly, SN 2009nr has a projected distance of 13.0 kpc (~4.3 disk scale lengths) from the nucleus of the small star-forming host galaxy UGC 8255. This indicates that the progenitor of SN 2009nr is not associated with a young stellar population, calling into question the conventional association of luminous SNe Ia with the "prompt" component directly correlated with current star formation. The pre-discovery observation of SN 2009nr using ASAS demonstrates the science utility of high cadence all sky surveys conducted using small telescopes for the discovery of nearby (d=<50 Mpc) supernovae.Comment: 11 pages, 11 figures, 4 tables. Accepted for publication in ApJ on 11/02/201

Six Months of Multi-Wavelength Follow-up of the Tidal Disruption Candidate ASASSN-14li and Implied TDE Rates from ASAS-SN

We present ground-based and Swift photometric and spectroscopic observations of the candidate tidal disruption event (TDE) ASASSN-14li, found at the center of PGC 043234 ($d\simeq90$ Mpc) by the All-Sky Automated Survey for SuperNovae (ASAS-SN). The source had a peak bolometric luminosity of $L\simeq10^{44}$ ergs s$^{-1}$ and a total integrated energy of $E\simeq7\times10^{50}$ ergs radiated over the $\sim6$ months of observations presented. The UV/optical emission of the source is well-fit by a blackbody with roughly constant temperature of $T\sim35,000$ K, while the luminosity declines by roughly a factor of 16 over this time. The optical/UV luminosity decline is broadly consistent with an exponential decline, $L\propto e^{-t/t_0}$, with $t_0\simeq60$ days. ASASSN-14li also exhibits soft X-ray emission comparable in luminosity to the optical and UV emission but declining at a slower rate, and the X-ray emission now dominates. Spectra of the source show broad Balmer and helium lines in emission as well as strong blue continuum emission at all epochs. We use the discoveries of ASASSN-14li and ASASSN-14ae to estimate the TDE rate implied by ASAS-SN, finding an average rate of $r \simeq 4.1 \times 10^{-5}~{\rm yr}^{-1}$ per galaxy with a 90% confidence interval of $(2.2 - 17.0) \times 10^{-5}~{\rm yr}^{-1}$ per galaxy. ASAS-SN found roughly 1 TDE for every 70 Type Ia supernovae in 2014, a rate that is much higher than that of other surveys.Comment: 21 pages, 9 figures, 6 tables. Photometric data presented in this submission are included as ancillary files. Manuscript updated to reflect changes made in the published version. For a brief video explaining this paper, see https://youtu.be/CTbr-d7cWZ

The Supernova Impostor Impostor SN 1961V: Spitzer Shows That Zwicky Was Right (Again)

SN 1961V, one of Zwicky's defining Type V supernovae (SN), was a peculiar transient in NGC 1058 that has variously been categorized as either a true core collapse SN leaving a black hole (BH) or neutron star (NS) remnant, or an eruption of a luminous blue variable (LBV) star. The former case is suggested by its association with a decaying non-thermal radio source, while the latter is suggested by its peculiar transient light curve and its low initial expansion velocities. The crucial difference is that the star survives a transient eruption but not an SN. All stars identified as possible survivors are significantly fainter, L_opt ~ 10^5 Lsun, than the L_opt ~ 3 10^6 Lsun progenitor star at optical wavelengths. While this can be explained by dust absorption in a shell of material ejected during the transient, the survivor must then be present as a L_IR ~ 3 10^6 Lsun mid-infrared source. Using archival Spitzer observations of the region, we show that such a luminous mid-IR source is not present. The brightest source of dust emission is only L_IR ~ 10^5 Lsun and does not correspond to the previously identified candidates for the surviving star. The dust cannot be made sufficiently distant and cold to avoid detection unless the ejection energy, mass and velocity scales are those of a SN or greater. We conclude that SN 1961V was a peculiar, but real, supernova. Its peculiarities are probably due to enhanced mass loss just prior to the SN, followed by the interactions of the SN blast wave with this ejecta. This adds to the evidence that there is a population of SN progenitors that have major mass loss episodes shortly before core collapse. The progenitor is a low metallicity, ~1/3 solar, high mass, M_ZAMS > 80 Msun, star, which means either that BH formation can be accompanied by an SN or that surprisingly high mass stars can form a NS.Comment: 26 pages, 7 figures, submitted to Ap