We present an exquisite 30 minute cadence Kepler (K2) light curve of the Type Ia supernova (SN Ia) 2018oh (ASASSN-18bt), starting weeks before explosion, covering the moment of explosion and the subsequent rise, and continuing past peak brightness. These data are supplemented by multi-color Panoramic Survey Telescope (Pan-STARRS1) and Rapid Response System 1 and Cerro Tololo Inter-American Observatory 4 m Dark Energy Camera (CTIO 4-m DECam) observations obtained within hours of explosion. The K2 light curve has an unusual twocomponent shape, where the flux rises with a steep linear gradient for the first few days, followed by a quadratic rise as seen for typical supernovae (SNe)Ia. This "flux excess" relative to canonical SNIa behavior is confirmed in our i-band light curve, and furthermore, SN 2018oh is especially blue during the early epochs. The flux excess peaks 2.14±0.04 days after explosion, has a FWHM of 3.12±0.04 days, a blackbody temperature of T 17, 500 9,000 11,500 =-+ K, a peak luminosity of 4.3 0.2 10 erg s 37 1 ´-, and a total integrated energy of 1.27 0.01 10 erg 43 ´. We compare SN 2018oh to several models that may provide additional heating at early times, including collision with a companion and a shallow concentration of radioactive nickel. While all of these models generally reproduce the early K2 light curve shape, we slightly favor a companion interaction, at a distance of ∼2 10 cm 12 based on our early color measurements, although the exact distance depends on the uncertain viewing angle. Additional confirmation of a companion interaction in future modeling and observations of SN 2018oh would provide strong support for a single-degenerate progenitor system.

New BV RI photometry and optical spectroscopy of the Type IIp supernova 2004dj in NGC 2403, obtained during the first year since discovery, are presented. The progenitor cluster, Sandage 96, is also detected on pre-explosion frames. The light curve indicates that the explosion occurred about 30 d before discovery, and the plateau phase lasted about +110 ± 20 d after that. The plateau-phase spectra have been modelled with the SYNOW spectral synthesis code using H, Na I, Ti II, Sc II, Fe II and Ba I lines. The SN distance is inferred from the expanding photosphere method and the standard candle method applicable for SNe IIp. They resulted in distances that are consistent with each other as well as earlier Cepheid and Tully-Fisher distances. The average distance, D = 3.47 ± 0.29 Mpc is proposed for SN 2004dj and NGC 2403. The nickel mass produced by the explosion is estimated as ∼0.02 ± 0.01 M . The spectral energy distribution of the progenitor cluster is reanalysed by fitting population synthesis models to our observed BV RI data supplemented by U and JHK magnitudes from the literature. The χ 2 minimization revealed a possible 'young' solution with cluster age T cl = 8 Myr, and an 'old' solution with T cl = 20-30 Myr. The 'young' solution would imply a progenitor mass M > 20 M , which is higher than the previously detected progenitor masses for Type II SNe.

We present extensive optical (UBV RI, ¢ ¢ ¢ ¢ g r i z , and open CCD) and near-infrared (ZY JH) photometry for the very nearby Type IIP SN 2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD 56496.9±0.3. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive UBV RIJHK bolometric calibrations from UBV RI and unfiltered measurements that potentially reach 2% precision with a B−V colordependent correction. We observe moderately strong Si II l6355 as early as +8 days. The photospheric velocity (v ph ) is determined by modeling the spectra in the vicinity of Fe II l5169 whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives =  v 4500 500 ph km s −1 at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10-12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be -+ 9.0 0.6 0.4 Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be 94±7 days long, yields an explosion energy of 0.9 0.3 10 51 erg, a final pre-explosion progenitor mass of 15.2±4.2  M and a radius of 250±70  R . We observe a broken exponential profile beyond +120 days, with a break point at +183±16 days. Measurements beyond this break time yield a 56 Ni mass of 0.013±0.001M  .

Supernova (SN) 2018oh (ASASSN-18bt) is the first spectroscopically confirmed Type Ia supernova (SN Ia) observed in the Kepler field. The Kepler data revealed an excess emission in its early light curve, allowing us to place interesting constraints on its progenitor system. Here we present extensive optical, ultraviolet, and nearinfrared photometry, as well as dense sampling of optical spectra, for this object. SN 2018oh is relatively normal in its photometric evolution, with a rise time of 18.3±0.3 days and Δm 15 (B)=0.96±0.03 mag, but it seems to have bluer B−V colors. We construct the "UVOIR" bolometric light curve having a peak luminosity of 1.49×10 43 erg s −1 , from which we derive a nickel mass as 0.55±0.04 M e by fitting radiation diffusion models powered by centrally located 56 Ni. Note that the moment when nickel-powered luminosity starts to emerge is +3.85 days after the first light in the Kepler data, suggesting other origins of the early-time emission, e.g., mixing of 56 Ni to outer layers of the ejecta or interaction between the ejecta and nearby circumstellar material or a nondegenerate companion star. The spectral evolution of SN 2018oh is similar to that of a normal SN Ia but is characterized by prominent and persistent carbon absorption features. The CII features can be detected from the early phases to about 3 weeks after the maximum light, representing the latest detection of carbon ever recorded in an SN Ia. This indicates that a considerable amount of unburned carbon exists in the ejecta of SN 2018oh and may mix into deeper layers.

The overtone and multi-mode RR Lyrae stars in the globular cluster M3 are studied using a 200 day long, B V , , and I C time-series photometry obtained in 2012. 70% of the 52 overtone variables observed show some kind of multi-periodicity (with additional frequency at f f 0.61 0.61 1O = frequency ratio, Blazhko effect, double/multi-mode pulsation, and period doubling). A signal at the 0.587 frequency ratio to the fundamental-mode frequency is detected in the double-mode star, V13, which may be identified as the second radial overtone mode. If this mode identification is correct, than V13 is the first RR Lyrae star showing triple-mode pulsation of the first three radial modes. Either the Blazhko effect or the f 0.61 frequency (or both of these phenomena) appears in seven doublemode stars. The P P 1O F period ratio of RRd stars showing the Blazhko effect are anomalous. A displacement of the main frequency component at the fundamental mode with the value of modulation frequency (or its half), is detected in three Blazhko RRd stars that are parallel with the appearance of the overtone-mode pulsation. The f 0.61 frequency appears in RRc stars that lie at the blue side of the double-mode region and in RRd stars, raising the suspicion that its occurrence may be connected to double-mode pulsation. The changes of the Blazhko and doublemode properties of the stars are also reviewed using the recent and archive photometric data.

Context. M31N 2015M31N -01a (or M31LRN 2015 is a red nova that erupted in January 2015 -the first event of this kind observed in M 31 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 the Large Altazimuth Telescope (BTA), the Gran Telecsopio Canarias (GTC) and the Rozhen 2 m telescope. Results. We present a highly accurate 70 d light curve and astrometry with a 0.05 uncertainty. The colour indices reached a minimum of 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 be 8.7 +3.3 −2.2 × 10 5 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.

Aims. The nearby, bright, almost completely unreddened Type Ia supernova 2011fe in M101 provides a unique opportunity to test both the precision and the accuracy of the extragalactic distances derived from SNe Ia light curve fitters. Methods. We applied the current, public versions of the independent light curve fitting codes MLCS2k2 and SALT2 to compute the distance modulus of SN 2011fe from high-precision, multi-color (BVRI) light curves. Results. The results from the two fitting codes confirm that 2011fe is a "normal" (not peculiar) and only slightly reddened SN Ia. New unreddened distance moduli are derived as 29.21 ± 0.07 mag (D ∼ 6.95 ± 0.23 Mpc, MLCS2k2), and 29.05 ± 0.07 mag (6.46 ± 0.21 Mpc). Conclusions. Despite the very good fitting quality achieved with both light curve fitters, the resulting distance moduli are inconsistent by 2σ. Both are marginally consistent (at ∼1σ) with the Hubble Space Telescope key project distance modulus for M101. The SALT2 distance is in good agreement with the recently revised Cepheid-and TRGB-distance to M101. Averaging all SN-and Cepheid-based estimates, the absolute distance to M101 is ∼6.6 ± 0.5 Mpc.

Abstract.A CCD photometric study of the dense galactic open cluster M 37 is presented and discussed. The majority of the analysed data are time-series measurements obtained through an RC filter. The observations were carried out on seven nights between December 1999 and February 2000, and have led to the discovery of 7 new variable stars in the field. Three of them have been unambiguously identified as W UMa-type eclipsing binaries, while two more are monoperiodic pulsating stars, most probably high-amplitude δ Scuti-type variables. The remaining two stars seem to be long-period eclipsing binaries without firm period determination. Johnson B and V frames have been used to construct a new colour-magnitude (CM) diagram of the cluster, and to find the locations of the new variable stars. The pulsating variables are most likely background objects. The CM diagram is fitted with recent isochrones yielding the main parameters of the cluster.