Large size and slow rotation of the trans-Neptunian object (225088) 2007 OR10 discovered from Herschel and K2 observations

We present the first comprehensive thermal and rotational analysis of the second most distant trans-Neptunian object (225088) 2007 OR10. We combined optical light curves provided by the Kepler space telescope -- K2 extended mission and thermal infrared data provided by the Herschel Space Observatory. We found that (225088) 2007 OR10 is likely to be larger and darker than derived by earlier studies: we obtained a diameter of d=1535^{+75}_{-225} km which places (225088) 2007 OR10 in the biggest top three trans-Neptunian objects. The corresponding visual geometric albedo is p_V=0.089^{+0.031}_{-0.009}. The light curve analysis revealed a slow rotation rate of P_rot=44.81+/-0.37 h, superseded by a very few objects only. The most likely light-curve solution is double-peaked with a slight asymmetry, however, we cannot safely rule out the possibility of having a rotation period of P_rot=22.40+/-0.18 h which corresponds to a single-peaked solution. Due to the size and slow rotation, the shape of the object should be a MacLaurin ellipsoid, so the light variation should be caused by surface inhomogeneities. Its newly derived larger diameter also implies larger surface gravity and a more likely retention of volatiles -- CH_4, CO and N_2 -- on the surface.Comment: Accepted for publication in AJ, 8 pages in emulateapj styl

The early phases of the type Iax supernova SN 2011ay

We present a detailed study of the early phases of the peculiar supernova 2011ay based on BVRI photometry obtained at Konkoly Observatory, Hungary, and optical spectra taken with the Hobby-Eberly Telescope at McDonald Observatory, Texas. The spectral analysis carried out with SYN++ and SYNAPPS confirms that SN 2011ay belongs to the recently defined class of SNe Iax, which is also supported by the prop- erties of its light and color curves. The estimated photospheric temperature around maximum light, Tphot ∼ 8,000 K, is lower than in most Type Ia SNe, which results in the appearance of strong Fe II features in the spectra of SN 2011ay, even during the early phases. We also show that strong blending with metal features (those of Ti II, Fe II, Co II) makes the direct analysis of the broad spectral features very difficult, and this may be true for all SNe Iax. We find two alternative spectrum models that both describe the observed spectra adequately, but their photospheric velocities differ by at least ∼ 3, 000 km s−1. The quasi-bolometric light curve of SN 2011ay has been assem- bled by integrating the UV-optical spectral energy distributions. Fitting a modified Arnett-model to Lbol(t), the moment of explosion and other physical parameters, i.e. the rise time to maximum, the 56Ni mass and the total ejecta mass are estimated as trise ∼14±1 days, MN i ∼0.22±0.01 M⊙ and Mej ∼ 0.8 M⊙, respectively

The January 2015 outburst of a red nova in M 31

Context. M31N 2015-01a (or M31LRN 2015) is a red nova that erupted in January 2015 – the first event of this kind observed in M31 since 1988. Very few similar events have been confirmed as of 2015. Most of them are considered to be products of stellar mergers.Aims. Results of an extensive optical monitoring of the transient in the period January-March 2015 are presented.Methods. Eight optical telescopes were used for imaging. Spectra were obtained on BTA, GTC and the Rozhen 2m telescope.Results. We present a highly accurate 70 d lightcurve and astrometry with a 0.05′′uncertainty. The color indices reached a minimum 2-3 d before peak brightness and rapidly increased afterwards. The spectral type changed from F5I to F0I in 6 d before the maximum and then to K3I in the next 30 d. The luminosity of the transient was estimated to 8.7+3.3 −2.2 × 105 L⊙ during the optical maximum.Conclusions. Both the photometric and the spectroscopic results confirm that the object is a red nova, similar to V838 Monocerotis

Searching for the Expelled Hydrogen Envelope in Type I Supernovae via Late-Time Hα Emission

We report the first results from our long-term observational survey aimed at discovering late-time interaction between the ejecta of hydrogen-poor Type I supernovae (SNe I) and the hydrogen-rich envelope expelled from the progenitor star several decades/centuries before explosion. The expelled envelope, moving with a velocity of ∼10–100 km s‑1, is expected to be caught up by the fast-moving SN ejecta several years/decades after explosion, depending on the history of the mass-loss process acting in the progenitor star prior to explosion. The collision between the SN ejecta and the circumstellar envelope results in net emission in the Balmer lines, especially Hα. We look for signs of late-time Hα emission in older SNe Ia/Ibc/IIb with hydrogen-poor ejecta via narrowband imaging. Continuum-subtracted Hα emission has been detected for 13 point sources: 9 SN Ibc, 1 SN IIb, and 3 SN Ia events. Thirty-eight SN sites were observed on at least two epochs, from which three objects (SN 1985F, SN 2005kl, and SN 2012fh) showed significant temporal variation in the strength of their Hα emission in our Direct Imaging Auxiliary Functions Instrument (DIAFI) data. This suggests that the variable emission is probably not due to nearby H ii regions unassociated with the SN and hence is an important additional hint that ejecta–circumstellar medium interaction may take place in these systems. Moreover, we successfully detected the late-time Hα emission from the Type Ib SN 2014C, which was recently discovered as a strongly interacting SN in various (radio, infrared, optical, and X-ray) bands

Photometric and radial-velocity time-series of RR Lyrae stars in M3: analysis of single-mode variables

We present the first simultaneous photometric and spectroscopic investigation of a large set of RR Lyrae variables in a globular cluster. The radial-velocity data presented comprise the largest sample of RVs of RR Lyrae stars ever obtained. The target is M3; BVI_C time-series of 111 and b flux data of further 64 RRab stars, and RV data of 79 RR Lyrae stars are published. Blazhko modulation of the light curves of 47 percent of the RRab stars are detected. The mean value of the center-of-mass velocities of RR Lyrae stars is −146.8 km/s with 4.52 km/s standard deviation, which is in vgood agreement with the results obtained for the red giants of the cluster. The Φ21 RV phase difference of the RV curves of RRab stars is found to be uniformly constant both for the M3 and for Galactic field RRab stars; no period or metallicity dependence of the Φ21 RV is detected. The Baade-Wesselink distances of 26 non-Blazhko variables with the best phase-coverage radial-velocity curves are determined; the corresponding distance of the cluster, 10480±210 pc, agrees with the previous literature information. A quadratic formula for the Apuls−AV relation of RRab stars is given, which is valid for both OoI and OoII variables. We also show that the (V − I)0 of RRab stars measured at light minimum is period dependent, there is at least 0.1 mag difference between the colours at minimum light of the shortest- and longest-period variables

Rotational Properties of Hilda Asteroids Observed by the K2 Mission

Hilda asteroids orbit at the outer edge, or just outside of the Main Belt, occupying the 2:3 mean motion resonance with Jupiter. It is known that the group shows a mixed taxonomy that suggests the mixed origin of Hilda members, having migrated to the current orbit both from the outer Main Belt and from the Trojans swarms. But there are still few observations for comparative studies that help in understanding the Hilda group in deeper details. We identified 125 individual light curves of Hilda asteroids observed by the K2 mission. We found that despite of the mixed taxonomies, the Hilda group highly resembles to the Trojans in the distribution of rotation periods and amplitudes, and even the LR group (mostly C and X-type) Hildas follow this rule. Contrary to the Main Belt, Hilda group lacks the very fast rotators. The ratio of extremely slow rotators (P>100 h) is a surprising 18%, which is unique in the Solar System. The occurrence rate of asteroids with multiple periods (4%) and asteroids with three maxima in the light curves (5%) can be signs of high rate of binarity, which we can estimate as 25% within the Hilda group

Physical properties of the extreme Centaur and super-comet candidate 2013 AZ 60

We present estimates of the basic physical properties – including size and albedo – of the extreme Centaur 2013 AZ60. These properties have been derived from optical and thermal infrared measurements. Our optical measurements revealed a likely full period of ≈ 9.4 h with a shallow amplitude of 4.5%. By combining optical brightness information and thermal emission data, we are able to derive a diameter of 62.3 ± 5.3 km and a geometric albedo of 2.9% – corresponding to an extremely dark surface. Additionally, our finding of & 50 Jm−2K−1s−1/2 for the thermal inertia is also noticeably for objects in such a distance. The results of dynamical simulations yield an unstable orbit, with a 50% probability that the target will be ejected from the Solar System within 700,000 years. The current orbit of this object as well as its instability could imply a pristine cometary surface. This possibility is in agreement with the observed low geometric albedo and red photometric colour indices for the object, which are a good match for the surface of a dormant comet – as would be expected for a long-period cometary body approaching perihelion. Despite the fact it was approaching ever closer to the Sun, however, the object exhibited star-like profiles in each of our observations, lacking any sign of cometary activity. By the albedo, 2013 AZ60 is a candidate for the darkest body among the known TNOs

The January 2015 outburst of a red nova in M31

M31N 2015-01a (or M31LRN 2015) is a red nova that erupted in January 2015 -- the first event of this kind observed in M31 since 1988. Very few similar events have been confirmed as of 2015. Most of them are considered to be products of stellar mergers. Results of an extensive optical monitoring of the transient in the period January-March 2015 are presented. Eight optical telescopes were used for imaging. Spectra were obtained on BTA, GTC and the Rozhen 2m telescope. We present a highly accurate 70 d lightcurve and astrometry with a 0.05" uncertainty. The color indices reached a minimum 2-3 d before peak brightness and rapidly increased afterwards. The spectral type changed from F5I to F0I in 6 d before the maximum and then to K3I in the next 30 d. The luminosity of the transient was estimated to $8.7^{+3.3}_{-2.2}\times10^{5}L_{\odot}$ during the optical maximum. Both the photometric and the spectroscopic results confirm that the object is a red nova, similar to V838 Monocerotis.Comment: 5 pages, 4 figures, 4 tables, accepted for publication in Astronomy and Astrophysics as a Letter to the Editor; page 5 is online material onl

SN 2017cfd: A Normal Type Ia Supernova Discovered Very Young

The Type Ia supernova (SN Ia) 2017cfd in IC 0511 (redshift z=0.01209 ± 0.00016) was discovered by the Lick Observatory Supernova Search 1.6 ± 0.7 day after the fitted first-light time (15.2 days before B-band maximum brightness). Photometric and spectroscopic follow-up observations show that SN 2017cfd is a typical, normal SN Ia with a peak luminosity MB ≈ -19.2± 0.2 mag, ∆m15(B) = 1.16 mag, and reached a B-band maximum ∼16.8 days after the first light. We estimate there to be moderately strong host-galaxy extinction (AV = 0.39 ± 0.03 mag) based on MLCS2k2 fitting. The spectrum reveals a Si II λ6355 velocity of ∼11,200 km s-1 at peak brightness. SN 2017cfd was discovered very young, with multiband data taken starting 2 days after the first light, making it a valuable complement to the currently small sample (fewer than a dozen) of SNe Ia time (B-V)0 color evolution belongs to the "blue" population rather than to the distinct "red" population. Using the photometry, we constrain the companion-star radius to be ≲2.5 R☉ with the Kasen model, thus ruling out a red-giant companion