Discovery of a Promissing Candidate of WZ Sge-Type Dwarf Novae, ASAS 160048-4846.2: Evidence for Double-Peaked Humps

We report on time-resolved CCD photometry during the 2005 June outburst of a dwarf nova, ASAS160048-4846.2. The observed light curves unambiguously showed embryonic humps with a period of 0.063381(41) days, after which genuine superhumps emerged with a period of 0.064927(3) days. Based on evidence for double-peaked humps in the earlier stage of the outburst, this object might be qualified as the seventh member of WZ Sge-type dwarf novae after Var Her 04. If the former period is the same as, or very close to the orbital period of the system, as in other WZ Sge systems, the fractional superhump excess is about 2.4{%}. This value is unexpectedly larger than that of other WZ Sge-type dwarf novae. The early phase of our observing run provided evidence for the transition from chaotic humps to genuine superhumps, together with increasing the amplitude.Comment: 4 pages, 6 figures, submitted to PAS

Photometric Studies of a WZ Sge-Type Dwarf Nova Candidate, ASAS160048-4846.2

We report on our time-resolved CCD photometry during the 2005 June superoutburst of a WZ Sge-type dwarf nova candidate, ASAS 160048-4846.2. The ordinary superhumps underwent a complex evolution during the superoutburst. The superhump amplitude experienced a regrowth, and had two peaks. The superhump period decreased when the superhump amplitude reached to the first maximum, successively gradually increased until the second maximum of the amplitude, and finally decreased again. Investigating other SU UMa-type dwarf novae which show an increase of the superhump period, we found the same trend of the superhump evolution in superoutbursts of them. We speculate that the superhump regrowth in the amplitude has a close relation to the increase of the superhump period, and all of SU UMa-type dwarf novae with a superhump regrowth follow the same evolution of the ordinary superhumps as that of ASAS 160048-4846.2.Comment: 7 pages, 4 figure

Explosion of a massive, He-rich star at z=0.16

We present spectroscopic and photometric data of the peculiar SN 2001gh, discovered by the 'Southern inTermediate Redshift ESO Supernova Search' (STRESS) at a redshift z=0.16. SN 2001gh has relatively high luminosity at maximum (M_B = -18.55 mag), while the light curve shows a broad peak. An early-time spectrum shows an almost featureless, blue continuum with a few weak and shallow P-Cygni lines that we attribute to HeI. HeI lines remain the only spectral features visible in a subsequent spectrum, obtained one month later. A remarkable property of SN 2001gh is the lack of significant spectral evolution over the temporal window of nearly one month separating the two spectra. In order to explain the properties of SN 2001gh, three powering mechanism are explored, including radioactive decays of a moderately large amount of 56Ni, magnetar spin-down, and interaction of SN ejecta with circumstellar medium. We favour the latter scenario, with a SN Ib wrapped in a dense, circumstellar shell. The fact that no models provide an excellent fit with observations, confirms the troublesome interpretation of the nature of SN 2001gh. A rate estimate for SN 2001gh-like event is also provided, confirming the intrinsic rarity of these objects.Comment: 11 pages, 8 figures, 3 tables. Accepted by MNRA

Inverse anisotropic diffusion from power density measurements in two dimensions

This paper concerns the reconstruction of an anisotropic diffusion tensor $\gamma=(\gamma_{ij})_{1\leq i,j\leq 2}$ from knowledge of internal functionals of the form $\gamma\nabla u_i\cdot\nabla u_j$ with $u_i$ for $1\leq i\leq I$ solutions of the elliptic equation $\nabla \cdot \gamma \nabla u_i=0$ on a two dimensional bounded domain with appropriate boundary conditions. We show that for I=4 and appropriately chosen boundary conditions, $\gamma$ may uniquely and stably be reconstructed from such internal functionals, which appear in coupled-physics inverse problems involving the ultrasound modulation of electrical or optical coefficients. Explicit reconstruction procedures for the diffusion tensor are presented and implemented numerically.Comment: 27 pages, 6 figure

The 2005 July Superoutburst of the Dwarf Nova 2QZ J021927.9-304545: the SU UMa Nature Confirmed

We report on time-resolved photometry of the 2005 July superoutburst of the dwarf nova, 2QZ J021927.9-304545. The resultant light curves showed conspicuous superhumps with a period of 0.081113(19) days, confirming the SU UMa nature of the object. Although we missed the maximum phase of the outburst, the amplitude of the superoutburst well exceeded 5 mag. This value is slightly larger than that of typical SU UMa-type dwarf novae. The superhump period decreased as time elapsed, as can be seen in most SU UMa-type dwarf novae. Based on the archive of ASAS-3, the recurrence time of a superoutburst of the variable turned out to be about 400 days. This value is typical of well known SU UMa stars. The distance to this system was roughly estimated as 370(+20, -60) pc using an empirical relation.Comment: 6 pages, 7 figures, accepted for publication in PAS

Photometric Studies of New Southern SU UMa-type dwarf novae, FL Triangulum Australe and CTCV J0549-4921

We report time-resolved optical CCD photometry on newly discovered SU UMa-type dwarf novae, FL TrA and CTCV J0549-4921. During the 2006 August outburst, we detected superhumps with a period of 0.59897(11) days for FL TrA, clarifying the SU UMa nature of the system. On the first night of our observations on FL TrA, the object showed no superhumps. This implies that it takes a few days for full development of superhumps. The superhump period variation diagram of FL TrA was similar to that observed in some WZ Sge stars and short period SU UMa-type stars. This indicates that the system is closely related to WZ Sge stars and SU UMa stars having short orbital periods. For CTCV J0549-4921, the candidates of the mean superhump period are 0.083249(10) days and 0.084257(8) days, respectively. Due to a lack of the observations, we cannot determine the true superhump period, but the latter period is favorable. Using the ASAS-3 archive, it turned out that the system shows only four outbursts over the past 6 years. The outburst amplitude of CTCV J0549-4921 was relatively small, with about 4.5 mag. One possibility is that mass evaporation may play a role during quiescence.Comment: 7 pages, 8 figures, published for PASJ vol.6

Constraints on the Progenitor of SN 2016gkg From Its Shock-Cooling Light Curve

SN 2016gkg is a nearby Type IIb supernova discovered shortly after explosion. Like several other Type IIb events with early-time data, SN 2016gkg displays a double-peaked light curve, with the first peak associated with the cooling of a low-mass extended progenitor envelope. We present unprecedented intranight-cadence multi-band photometric coverage of the first light-curve peak of SN 2016gkg obtained from the Las Cumbres Observatory Global Telescope network, the Asteroid Terrestrial-impact Last Alert System, the Swift satellite and various amateur-operated telescopes. Fitting these data to analytical shock-cooling models gives a progenitor radius of ~25-140 solar radii with ~2-30 x 10^-2 solar masses of material in the extended envelope (depending on the model and the assumed host-galaxy extinction). Our radius estimates are broadly consistent with values derived independently (in other works) from HST imaging of the progenitor star. However, the shock-cooling model radii are on the lower end of the values indicated by pre-explosion imaging. Hydrodynamical simulations could refine the progenitor parameters deduced from the shock-cooling emission and test the analytical models.Comment: Accepted by ApJ

The beta Pictoris association: Catalog of photometric rotational periods of low-mass members and candidate members

We intended to compile the most complete catalog of bona fide members and candidate members of the beta Pictoris association, and to measure their rotation periods and basic properties from our own observations, public archives, and exploring the literature. We carried out a multi-observatories campaign to get our own photometric time series and collected all archived public photometric data time series for the stars in our catalog. Each time series was analyzed with the Lomb-Scargle and CLEAN periodograms to search for the stellar rotation periods. We complemented the measured rotational properties with detailed information on multiplicity, membership, and projected rotational velocity available in the literature and discussed star by star. We measured the rotation periods of 112 out of 117 among bona fide members and candidate members of the beta Pictoris association and, whenever possible, we also measured the luminosity, radius, and inclination of the stellar rotation axis. This represents to date the largest catalog of rotation periods of any young loose stellar association. We provided an extensive catalog of rotation periods together with other relevant basic properties useful to explore a number of open issues, such as the causes of spread of rotation periods among coeval stars, evolution of angular momentum, and lithium-rotation connection.Comment: Forthcoming article, Received: 20 June 2016 / Accepted: 09 September 2016; 40 pages, 2 figures. The online figures A1-A73 are available at CD