K. Sarneczky

Improved distance determination to M 51 from supernovae 2011dh and 2005cs

Aims. The appearance of two recent supernovae, SN 2011dh and 2005cs, both in M 51, provides an opportunity to derive an improved distance to their host galaxy by combining the observations of both SNe. Methods. We apply the Expanding Photosphere Method to get the distance to M 51 by fitting the data of these two SNe simultaneously. In order to correct for the effect of flux dilution, we use correction factors (ζ) appropriate for standard type II-P SNe atmospheres for 2005cs, but find ζ ∼ 1 for the type IIb SN 2011dh, which may be due to the reduced H-content of its ejecta. Results. The EPM analysis resulted in D M5 1 = 8.4 ± 0.7 Mpc. Based on this improved distance, we also re-analyze the HST observations of the proposed progenitor of SN 2011dh. We confirm that the object detected on the pre-explosion HST-images is unlikely to be a compact stellar cluster. In addition, its derived radius (∼277 R� ) is too large for being the real (exploded) progenitor of SN 2011dh. Conclusions. The supernova-based distance, D = 8.4 Mpc, is in good agreement with other recent distance estimates to M 51.

The young, massive, star cluster Sandage-96 after the explosion of supernova 2004dj in NGC 2403

The bright Type II-plateau supernova (SN) 2004dj occurred within the young, massive stellar cluster Sandage-96 in a spiral arm of NGC 2403. New multiwavelength observations obtained with several ground-based and space-based telescopes were combined to study the radiation from Sandage-96 after SN 2004dj faded away. Sandage-96 started to dominate the flux in the optical bands starting from 2006 September (~800 days after explosion). The optical fluxes are equal to the pre-explosion ones within the observational uncertainties. An optical Keck spectrum obtained ~900 days after explosion shows the dominant blue continuum from the cluster stars shortward of 6000? ? as well as strong SN nebular emission lines redward. The integrated spectral energy distribution (SED) of the cluster has been extended into the ultraviolet region by archival XMM-Newton and new Swift observations, and compared with theoretical models. The outer parts of the cluster have been resolved by the Hubble Space Telescope, allowing the construction of a color-magnitude diagram (CMD). The fitting of the cluster SED with theoretical isochrones results in cluster ages distributed between 10 and 40 Myr, depending on the assumed metallicity and the theoretical model family. The isochrone fitting of the CMDs indicates that the resolved part of the cluster consists of stars having a bimodal age distribution: a younger population at ~10-16 Myr and an older one at ~32-100? Myr. The older population has an age distribution similar to that of the other nearby field stars. This may be explained with the hypothesis that the outskirts of Sandage-96 are contaminated by stars captured from the field during cluster formation. The young age of Sandage-96 and the comparison of its pre and postexplosion SEDs suggest 12 M prog 20 M ? as the most probable mass range for the progenitor of SN 2004dj. This is consistent with, but perhaps slightly higher than, most of the other Type II-plateau SN progenitor masses determined so far.

Testing supernovae Ia distance measurement methods with SN 2011fe

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. 5M pc.

Analysis of the rotation period of asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger - search for the YORP effect

Context. The spin state of small asteroids can change on a long timescale by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises from anisotropically scattered sunlight and proper thermal radiation from an irregularly-shaped asteroid. The secular change in the rotation period caused by the YORP effect can be detected by analysis of asteroid photometric lightcurves. Aims. We analyzed photometric lightcurves of near-Earth asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger with the aim to detect possible deviations from the constant rotation caused by the YORP effect. Methods. We carried out new photometric observations of the three asteroids, combined the new lightcurves with archived data, and used the lightcurve inversion method to model the asteroid shape, pole direction, and rotation rate. The YORP effect was modeled as a linear change in the rotation rate in time dω/dt .V alues of dω/dt derived from observations were compared with the values predicted by theory. Results. We derived physical models for all three asteroids. We had to model Eger as a nonconvex body because the convex model failed to fit the lightcurves observed at high phase angles. We probably detected the acceleration of the rotation rate of Eger dω/dt = (1.4 ± 0.6) × 10 −8 rad d −2 (3σ error), which corresponds to a decrease in the rotation period by 4. 2m s yr −1 . The photometry of Cerberus and Ra-Shalom was consistent with a constant-period model, and no secular change in the spin rate was detected. We could only constrain maximum values of |dω/dt| < 8 × 10 −9 rad d −2 for Cerberus, and |dω/dt| < 3 × 10 −8 rad d −2 for Ra-Shalom.

Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin

Aims. The transiting planet WASP-12 b was identified as a potential target for transit-timing studies because a departure from a linear ephemeris has been reported in the literature. Such deviations could be caused by an additional planet in the system. We attempt to confirm the claimed variations in transit timing and interpret their origin. Methods. We organised a multi-site campaign to observe transits by WASP-12 b in three observing seasons, using 0.5–2.6-metre telescopes. Results. We obtained 61 transit light curves, many of them with sub-millimagnitude precision. The simultaneous analysis of the best-quality datasets allowed us to obtain refined system parameters, which agree with values reported in previous studies. The residuals versus a linear ephemeris reveal a possible periodic signal that may be approximated by a sinusoid with an amplitude of 0.00068 ± 0.00013 d and period of 500 ± 20 orbital periods of WASP-12 b. The joint analysis of timing data and published radial velocity measurements results in a two-planet model that explains observations better than do single-planet scenarios. We hypothesise that WASP-12 b might not be the only planet in the system, and there might be the additional 0.1 MJup body on a 3.6-d eccentric orbit. A dynamical analysis indicates that the proposed two-planet system is stable on long timescales.

Distance of the hypernova SN 2002ap via the expanding photosphere method

New optical photometric and spectroscopic data of the bright hypernova SN 2002ap are presented. The obtained BVRI light curves as well as the optical spectra agree well with other published data series. The distance has been inferred by applying the Expanding Photosphere Method for the data around maximum. The derived 6.7 Mpc is in good agreement with recent photometric distances of M 74. However, the total (random plus systematic) uncertainty of the EPM-distance is at least ±4.5 Mpc (about 70%). The physical parameters of the SN have been determined via simplified analytic models of the light and velocity curves. It is confirmed that SN 2002ap was a less energetic hypernova, the kinetic energy was 4−8 × 10 51 erg, and the reddening-free absolute bolometric magnitude reached −16.63 mag (corresponding to Lbol = 3.47 × 10 8 L� ), about 2 mag less than the prototype hypernova SN 1998bw.

The Type Ia Supernova 2001V in NGC 3987

CCD photometry is presented of the type Ia SN 2001V occurred in the edge-on spiral galaxy NGC 3987. The observations made through Johnson-Cousins BVRI filters were collected from Feb. 24 (t = -8 days, with respect to B-maximum), up to May 5 (t = +62 days). The light curves are analyzed with the revised Multi-Colour Light Curve Shape (MLCS) method (Riess et al. 1998) by fitting template vectors to the observed light curves simultaneously. The reddening of SN 2001V is estimated to be E(B - V) = 0.05 mag, while the galactic component is E(B - V) = 0.02 mag (Schlegel et al. 1998), suggesting that part of the reddening may be due to the ISM in the host galaxy. The A parameter in MLCS converged to -0.47 mag, indicating that this SN was overluminous relative to the majority of Type Ia SNe. The inferred distance to its host galaxy, NGC 3987, is 74.5 ′ 5 Mpc, which is in good agreement with recently determined kinematic distances, based on radial velocity corrected for Virgo-infall and Hubble constant H 0 = 65 km s - 1 Mpc - 1 .

EXTENSIVE SPECTROSCOPY and PHOTOMETRY of the TYPE IIP SUPERNOVA 2013ej

We present extensive optical (UBV RI, {g} \prime {r} \prime {i} \prime {z} \prime , 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 color-dependent correction. We observe moderately strong Si ii λ 6355 as early as +8 days. The photospheric velocity ({v} {{ph }}) is determined by modeling the spectra in the vicinity of Fe ii λ 5169 whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives {v} {{ph }}=4500+/- 500 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} ȯ and a radius of 250 ± 70 {R} ȯ . 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 {} ȯ .

Exploring the circumstellar environment of the young eruptive star V2492 Cygni

Context. V2492 Cyg is a young eruptive star that went into outburst in 2010. The near-infrared color changes observed since the outburst peak suggest that the source belongs to a newly defined sub-class of young eruptive stars, where time-dependent accretion and variable line-of-sight extinction play a combined role in the flux changes. Aims. In order to learn about the origin of the light variations and to explore the circumstellar and interstellar environment of V2492 Cyg, we monitored the source at ten different wavelengths, between 0.55 μm and 2.2 μm from the ground and between 3.6 μm and 160 μm from space. Methods. We analyze the light curves and study the color−color diagrams via comparison with the standard reddening path. We examine the structure of the molecular cloud hosting V2492 Cyg by computing temperature and optical depth maps from the far-infrared data. Results. We find that the shapes of the light curves at different wavelengths are strictly self-similar and that the observed variability is related to a single physical process, most likely variable extinction. We suggest that the central source is episodically occulted by a dense dust cloud in the inner disk and, based on the invariability of the far-infrared fluxes, we propose that it is a long-lived rather than a transient structure. In some respects, V2492 Cyg can be regarded as a young, embedded analog of UX Orionis-type stars. Conclusions. The example of V2492 Cyg demonstrates that the light variations of young eruptive stars are not exclusively related to changing accretion. The variability provided information on an azimuthally asymmetric structural element in the inner disk. Such an asymmetric density distribution in the terrestrial zone may also have consequences for the initial conditions of planet formation.

Photometric observations of distant active comets

We present CCD VRC observations of 6 distant comets located at heliocentric distances of 3.4{7.2 AU. Time-series data were obtained on three nights in July, 2000 covering 16 hours. Each comet was observed after the perihelion, when a lower activity was expected. Contrary to expectation, we found well-dened circular comae and extended tails visible out to a few (3{5) arcmin. We detected a quasi-cyclic light variation of C/1999 J2, while C/1999 N4 showed some hints of a more complex variation. C/2000 K1 was constant to0:04 mag during the observing run. The standard V and RC data were used to estimate nuclear diameters, while the colour indices implied a slighly reddish (V R =0 : 68, C/2000 K1), a neutral (V R =0 : 47, C/1999 N4) and a slightly bluish (V R =0 : m 25, C/1999 J2) coma. Simple ts of the surface brightness distributions are also presented enabling order of magnitude estimates of nuclear radii. Beside the time-series observations, further single-shot observations of three faint comets are briefly described.