We obtained late-time optical and near-IR imaging of SN 2008S with the Large Binocular Telescope (LBT), near-IR data with the Hubble Space Telescope (HST), and mid-IR data with the Spitzer Space ...Telescope (SST). We find that (1) it is again invisible at optical (UBVR) wavelengths to magnitude limits of approximately 25 mag, (2) while detected in the near-IR (H) at approximately 24.8 mag, it is fading rapidly, and (3) it is still brighter than the progenitor at 3.6 and 4.5 microns in the mid-IR with a slow, steady decline. The IR detections in December 2010 are consistent with dust emission at a blackbody temperature of T ~ 640 K and a total luminosity of L ~ 200000 Lsun, much higher than the L ~ 40000 Lsun luminosity of the obscured progenitor star. The local environment also shows no evidence for massive (M >= 10 Msun) stars in the vicinity of the transient, consistent with the progenitor being a massive AGB star.
The progenitors of SN 2008S and the 2008 transient in NGC300 were dust-enshrouded, with extremely red mid-infrared (MIR) colors and relatively low luminosities. The transients were optically faint ...(-13 < M_V < -15) compared to normal core-collapse supernovae (SNe), and their spectra exhibited narrow emission lines. These events are unique among transient-progenitor pairs and hence constitute a new class. Whether they are true SNe or bright massive-star eruptions, we argue that their rate is ~20% of the SN rate. This fact is remarkable in light of the observation that a very small fraction of all massive stars have the MIR colors of the SN 2008S and NGC300 progenitors, as we show using MIR and optical luminosity, color, and variability properties of massive stars in M33. We find that the fraction of massive stars with colors consistent with these progenitors is 1/10000. In fact, only < 10 similar objects exist in M33 - all of which lie at the luminous red extremum of the AGB sequence. That these transients are relatively common with respect to SNe, while their progenitors are rare compared to the massive star population, implies that the dust-enshrouded phase is a short-lived phase in the lives of many massive stars. This shrouded epoch can occur only in the last ~10^4 yr before explosion, be it death or merely eruption. We discuss the implications of this finding for the evolution and census of ``low-mass'' massive stars (8-12 Msun), and we connect it with theoretical discussions of electron-capture SNe and the explosive birth of white dwarfs. A systematic census with (warm) Spitzer of galaxies in the local universe for analogous progenitors would significantly improve our knowledge of this channel to massive stellar explosions, and potentially to others with obscured progenitors. (Abridged)
We present the discovery and follow-up observations of SN 2008jb, a core-collapse supernova in the dwarf irregular galaxy ESO 302-14 at 9.6 Mpc. This transient was missed by galaxy-targeted surveys ...and was only found in archival optical images obtained by CRTS and ASAS. It was detected shortly after explosion and reached a bright optical maximum, Vmax = 13.6 mag (M_Vmax ~ -16.5). The shape of the light curve shows a plateau of 100 days, followed by a drop of 1.4 mag in V-band to a decline with the approximate Co 56 decay slope, consistent with 0.04 Msun of Ni 56 synthesized in the explosion. A spectrum obtained 2 years after explosion shows a broad, boxy Halpha emission line, which is unusual for type IIP supernovae. We detect the supernova in archival Spitzer and WISE images obtained 8-14 months after explosion, which show clear signs of warm dust emission. The dwarf irregular host galaxy has a low gas-phase oxygen abundance, 12 + log(O/H) = 8.2 (~1/5 Solar), similar to those of the SMC and the hosts of long gamma-ray bursts and luminous core-collapse supernovae. We study the host environment using GALEX FUV, R-band, and Halpha images and find that the supernova occurred in a large star-formation complex. The morphology of the Halpha emission appears as a large shell (R = 350 pc) surrounding the FUV and optical emission. We estimate an age of ~9 Myr and a total mass of ~2 x 10^5 Msun for the star-formation complex. These properties are consistent with the expanding Halpha supershells observed in well-studied nearby dwarf galaxies, which are tell-tale signs of feedback from the cumulative effect of massive star winds and supernovae. The age estimated for the star-forming region suggests a relatively high-mass progenitor star with initial mass of ~20 Msun. We discuss the implications of these findings in the study of core-collapse supernova progenitors. (Abridged)
The Panchromatic Hubble Andromeda Treasury (PHAT) is an on-going HST Multicycle Treasury program to image ~1/3 of M31's star forming disk in 6 filters, from the UV to the NIR. The full survey will ...resolve the galaxy into more than 100 million stars with projected radii from 0-20 kpc over a contiguous 0.5 square degree area in 828 orbits, producing imaging in the F275W and F336W filters with WFC3/UVIS, F475W and F814W with ACS/WFC, and F110W and F160W with WFC3/IR. The resulting wavelength coverage gives excellent constraints on stellar temperature, bolometric luminosity, and extinction for most spectral types. The photometry reaches SNR=4 at F275W=25.1, F336W=24.9, F475W=27.9, F814W=27.1, F110W=25.5, and F160W=24.6 for single pointings in the uncrowded outer disk; however, the optical and NIR data are crowding limited, and the deepest reliable magnitudes are up to 5 magnitudes brighter in the inner bulge. All pointings are dithered and produce Nyquist-sampled images in F475W, F814W, and F160W. We describe the observing strategy, photometry, astrometry, and data products, along with extensive tests of photometric stability, crowding errors, spatially-dependent photometric biases, and telescope pointing control. We report on initial fits to the structure of M31's disk, derived from the density of RGB stars, in a way that is independent of the assumed M/L and is robust to variations in dust extinction. These fits also show that the 10 kpc ring is not just a region of enhanced recent star formation, but is instead a dynamical structure containing a significant overdensity of stars with ages >1 Gyr. (Abridged)
Recent high-resolution spectra of z ~ 2 quasars suggest that Ly α clouds may have much lower temperatures (T ~ 5000 K) than previously thought (T ~ 30 000 K). This result is very uncertain at ...present, and there are still considerable differences between different groups of observers. In this paper we perform calculations based on the standard pressure-confined model of Ly α clouds in order to test the possibility of obtaining such low temperatures. Our results suggest that it may be difficult to explain temperatures as low as 5000 K using the standard pressure-confined model of the clouds. We also give many observational predictions which may in the future allow the accuracy of the model to be tested.
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 sub-types 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 sub-types of SNe Ia for the first time. The major sub-types 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.
We report the identification of a new, long period detached eclipsing binary
by the All-Sky Automated Survey for Supernovae (ASAS-SN). Combining V-band
photometry from ASAS-SN, ASAS and KELT, we ...constructed a light curve spanning
2006-2018. ASASSN-V J192543.72+402619.0 is an eccentric detached eclipsing
binary with an orbital period of $P\sim7.3$ yr, a minimum orbital eccentricity
of $e_{min}\sim0.2$ and a primary eclipse lasting $\sim160$ d. We also detect a
secondary eclipse that is $\sim 0.6$ mag shallower. Multi-band photometry
suggests that the more luminous component of the binary is an M-giant. Further
photometric and spectroscopic observations are encouraged.
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.
We report the discovery of KELT-2Ab, a hot Jupiter transiting the bright (V=8.77) primary star of the HD 42176 binary system. The host is a slightly evolved late F-star likely in the very short-lived ..."blue-hook" stage of evolution, with \(\teff=6148\pm48{\rm K}\), \(\log{g}=4.030_{-0.026}^{+0.015}\) and \(\feh=0.034\pm0.78\). The inferred stellar mass is \(M_*=1.314_{-0.060}^{+0.063}\)\msun\ and the star has a relatively large radius of \(R_*=1.836_{-0.046}^{+0.066}\)\rsun. The planet is a typical hot Jupiter with period \(4.11379\pm0.00001\) days and a mass of \(M_P=1.524\pm0.088\)\mj\ and radius of \(R_P=1.290_{-0.050}^{+0.064}\)\rj. This is mildly inflated as compared to models of irradiated giant planets at the \(\sim\)4 Gyr age of the system. KELT-2A is the third brightest star with a transiting planet identified by ground-based transit surveys, and the ninth brightest star overall with a transiting planet. KELT-2Ab's mass and radius are unique among the subset of planets with \(V<9\) host stars, and therefore increases the diversity of bright benchmark systems. We also measure the relative motion of KELT-2A and -2B over a baseline of 38 years, robustly demonstrating for the first time that the stars are bound. This allows us to infer that KELT-2B is an early K-dwarf. We hypothesize that through the eccentric Kozai mechanism KELT-2B may have emplaced KELT-2Ab in its current orbit. This scenario is potentially testable with Rossiter-McLaughlin measurements, which should have an amplitude of \(\sim\)44 m s\(^{-1}\).
A new link in the causal mapping between massive stars and potentially fatal explosive transients opened with the 2008 discovery of the dust-obscured progenitors of the luminous outbursts in NGC 6946 ...and NGC 300. Here we carry out a systematic mid-IR photometric search for massive, luminous, self-obscured stars in four nearby galaxies: M33, NGC 300, M81, and NGC 6946. For detection, we use only the 3.6 micron and 4.5 micron IRAC bands, as these can still be used for multi-epoch Spitzer surveys of nearby galaxies (=<10 Mpc). We combine familiar PSF and aperture-photometry with an innovative application of image subtraction to catalog the self-obscured massive stars in these galaxies. In particular, we verify that stars analogous to the progenitors of the NGC 6946 (SN 2008S) and NGC 300 transients are truly rare in all four galaxies: their number may be as low as ~1 per galaxy at any given moment. This result empirically supports the idea that the dust-enshrouded phase is a very short-lived phenomenon in the lives of many massive stars and that these objects constitute a natural extension of the AGB sequence. We also provide mid-IR catalogs of sources in NGC 300, M81, and NGC 6946.
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