Twelve type II-P supernovae seen with the eyes of Spitzer

Core-collapse supernovae (CC SNe), especially those of type II-plateau (II-P), are thought to be important contributors to cosmic dust production. The most obvious indicator of the presence of newly-formed and/or pre-existing dust is the time-dependent mid-infrared (MIR) excess coming from the environment of SNe. Our goal was to collect publicly available, previously unpublished measurements on type II-P (or peculiar IIP) SNe from the Spitzer database. The temporal changes of the observed fluxes may be indicative of the underlying supernova, while spectral energy distribution (SED) fitting to the fluxes in different IRAC channels may reveal the physical parameters of the mid-IR radiation, presumably due to warm dust. IRS spectra were extracted and calibrated with SPICE, while photometric SEDs were assembled using IRAF and MOPEX. Calculated SEDs from observed fluxes were fit with simple dust models to get basic information on the dust presumed as the source of MIR radiation. We found twelve SNe satisfying the criterion above, observed at late-time epochs (typically after +300 days). In three cases we could not identify any point source at the SN position on late time IRAC images. We found two SNe, 2005ad and 2005af, which likely have newly-formed dust in their environment, while in the other seven cases the observed MIR flux may originate from pre-existing circumstellar or interstellar dust. Our results support the previous observational conclusions that warm new dust in the environment of SNe contributes only marginally to cosmic dust content.Comment: Accepted for publication in Astronomy and Astrophysics; 15 pages, 8 figures, 9 tables (Ver. 2.: language edited version, minor corrections were made in the title, in the text, and in the reference list

The contact binary VW Cephei revisited: surface activity and period variation

Context. Despite the fact that VW Cephei is one of the well-studied contact binaries in the literature, there is no fully consistent model available that can explain every observed property of this system. Aims. Our motivation is to obtain new spectra along with photometric measurements, to analyze what kind of changes may have happened in the system in the past two decades, and to propose new ideas for explaining them. Methods. For the period analysis we determined 10 new times of minima from our light curves, and constructed a new O$-$C diagram of the system. Radial velocities of the components were determined using the cross-correlation technique. The light curves and radial velocities were modelled simultaneously with the PHOEBE code. All observed spectra were compared to synthetic spectra and equivalent widths of the H$\alpha$ line were measured on their differences. Results. We have re-determined the physical parameters of the system according to our new light curve and spectral models. We confirm that the primary component is more active than the secondary, and there is a correlation between spottedness and the chromospheric activity. We propose that flip-flop phenomenon occurring on the primary component could be a possible explanation of the observed nature of the activity. To explain the period variation of VW Cep, we test two previously suggested scenarios: presence of a fourth body in the system, and the Applegate-mechanism caused by periodic magnetic activity. We conclude that although none of these mechanisms can be ruled out entirely, the available data suggest that mass transfer with a slowly decreasing rate gives the most likely explanation for the period variation of VW Cep.Comment: 13 pages, 18 figures, 9 tables, accepted for publication in Astronomy and Astrophysic

Mass and orbit constraints of the gamma-ray binary LS 5039

We present the results of space-based photometric and ground-based spectroscopic observing campaigns on the gamma-ray binary LS 5039. The new orbital and physical parameters of the system are similar to former results, except we found a lower eccentricity. Our MOST-data show that any broad-band optical photometric variability at the orbital period is below the 2 mmag level. Light curve simulations support the lower value of eccentricity and imply that the mass of the compact object is higher than 1.8 solar masses.Comment: 2 pages, 1 figure (with 2 panels); to be published in the Proceedings: From Interacting Binaries to Exoplanets: Essential Modeling Tools, IAU Symposium 282 (18-22 July, 2011, Tatranska Lomnica, Slovakia

Exact Methods for the Longest Induced Cycle Problem

The longest induced (or chordless) cycle problem is a graph problem classified as NP-complete and involves the task of determining the largest possible subset of vertices within a graph in such a way that the induced subgraph forms a cycle. Within this paper, we present three integer linear programs specifically formulated to yield optimal solutions for this problem. The branch-and-cut algorithm has been used for two models. To demonstrate the computational efficiency of these methods, we utilize them on a range of real-world graphs as well as random graphs. Additionally, we conduct a comparative analysis against approaches previously proposed in the literature

Symbolic regression for approximating graph geodetic number

Graph properties are certain attributes that could make the structure of the graph understandable. Occasionally, standard methods cannot work properly for calculating exact values of graph properties due to their huge computational complexity, especially for real-world graphs. In contrast, heuristics and metaheuristics are alternatives proved their ability to provide sufficient solutions in a reasonable time. Although in some cases, even heuristics are not efficient enough, where they need some not easily obtainable global information of the graph. The problem thus should be dealt in completely different way by trying to find features that related to the property and based on these data build a formula which can approximate the graph property. In this work, symbolic regression with an evolutionary algorithm called Cartesian Genetic Programming has been used to derive formulas capable to approximate the graph geodetic number which measures the minimal-cardinality set of vertices, such that all shortest paths between its elements cover every vertex of the graph. Finding the exact value of the geodetic number is known to be NP-hard for general graphs. The obtained formulas are tested on random and real-world graphs. It is demonstrated how various graph properties as training data can lead to diverse formulas with different accuracy. It is also investigated which training data are really related to each property

The Broad-Lined Type IC SN 2012ap and the Nature of Relativistic Supernovae Lacking a Gamma-Ray Burst Detection

We present ultraviolet, optical, and near-infrared observations of SN 2012ap, a broad-lined Type Ic supernova in the galaxy NGC 1729 that produced a relativistic and rapidly decelerating outflow without a gamma-ray burst signature. Photometry and spectroscopy follow the flux evolution from –13 to +272 days past the B-band maximum of –17.4 ± 0.5 mag. The spectra are dominated by Fe II, O I, and Ca II absorption lines at ejecta velocities of v ≈ 20,000 km s–1 that change slowly over time. Other spectral absorption lines are consistent with contributions from photospheric He I, and hydrogen may also be present at higher velocities (v 27,000 km s–1). We use these observations to estimate explosion properties and derive a total ejecta mass of ~2.7 M ☉, a kinetic energy of ~1.0 × 1052 erg, and a 56Ni mass of 0.1-0.2 M ☉. Nebular spectra (t \u3e 200 days) exhibit an asymmetric double-peaked [O I] λλ6300, 6364 emission profile that we associate with absorption in the supernova interior, although toroidal ejecta geometry is an alternative explanation. SN 2012ap joins SN 2009bb as another exceptional supernova that shows evidence for a central engine (e.g., black hole accretion or magnetar) capable of launching a non-negligible portion of ejecta to relativistic velocities without a coincident gamma-ray burst detection. Defining attributes of their progenitor systems may be related to notable observed properties including environmental metallicities of Z \u3e Z ☉, moderate to high levels of host galaxy extinction (E(B – V) \u3e 0.4 mag), detection of high-velocity helium at early epochs, and a high relative flux ratio of [Ca II]/[O I] \u3e1 at nebular epochs. These events support the notion that jet activity at various energy scales may be present in a wide range of supernovae

The Unusually Luminous Extragalactic Nova SN 2010U

We present observations of the unusual optical transient SN 2010U, including spectra taken 1.03 days to 15.3 days after maximum light that identify it as a fast and luminous Fe II type nova. Our multi-band light curve traces the fast decline (t_2 = 3.5 days) from maximum light (M_V = -10.2 mag), placing SN 2010U in the top 0.5% of the most luminous novae ever observed. We find typical ejecta velocities of approximately 1100 km/s and that SN 2010U shares many spectral and photometric characteristics with two other fast and luminous Fe II type novae, including Nova LMC 1991 and M31N-2007-11d. For the extreme luminosity of this nova, the maximum magnitude vs. rate of decline relationship indicates a massive white dwarf progenitor with a low pre-outburst accretion rate. However, this prediction is in conflict with emerging theories of nova populations, which predict that luminous novae from massive white dwarfs should preferentially exhibit an alternate spectral type (He/N) near maximum light.Comment: 16 pages, 16 figures. Submitted to the Astrophysical Journa

Improved distance determination to M51 from supernovae 2011dh and 2005cs

The appearance of two recent supernovae, SN 2011dh and 2005cs, both in M51, provides an opportunity to derive an improved distance to their host galaxy by combining the observations of both SNe. We apply the Expanding Photosphere Method to get the distance to M51 by fitting the data of these two SNe simultaneously. In order to correct for the effect of flux dilution, we use correction factors (zeta) appropriate for standard type II-P SNe atmospheres for 2005cs, but find zeta ~ 1 for the type IIb SN 2011dh, which may be due to the reduced H-content of its ejecta. The EPM analysis resulted in D_M51 = 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_sun) is too large for being the real (exploded) progenitor of SN 2011dh. The supernova-based distance, D = 8.4 Mpc, is in good agreement with other recent distance estimates to M51.Comment: 6 pages, 5 figures, accepted for publication in A&

A Near-Infrared (JHK) Survey of the Vicinity of the HII region NGC 7538: Evidence for a Young Embedded Cluster

We describe the results of two near infrared (K-band) imaging surveys and a three color (JHK) survey of the vicinity of NGC 7538. The limiting magnitudes are K ~ 16.5 and K ~ 17.5 mag for the K-band surveys and K ~ 15 mag for the JHK survey. We identify more than 2000 and 9000 near-infrared (NIR) sources on the images of the two K-band surveys and 786 NIR sources in the JHK survey. From color-color diagrams, we derive a reddening law for background stars and identify 238 stars with NIR excesses. Contour maps indicate a high density peak coincident with a concentration of stars with NIR excesses. We identify this peak as a young, embedded cluster and confirm this result with the K-band luminosity function, color histograms, and color-magnitude diagrams. The center of the cluster is at RA = 23:13:39.34, DEC = 61:29:18.9. The cluster radius is $\sim$ 3' ~ 2.5 pc for an adopted distance, d ~ 2.8 kpc. For d = 2.8 kpc, and reddening, E_{J-K} = 0.55 mag, the slope of the logarithmic K-band luminosity function (KLF) of the cluster, s ~ 0.32 +- 0.03, agrees well with previous results for L1630 (s = 0.34) and M17 (s = 0.26).Comment: 26 pages with 11 figures. Accepted by Astronomical Journa

Spectroscopy of superluminous supernova host galaxies. A preference of hydrogen-poor events for extreme emission line galaxies

Superluminous supernovae (SLSNe) are very bright explosions that were only discovered recently and that show a preference for occurring in faint dwarf galaxies. Understanding why stellar evolution yields different types of stellar explosions in these environments is fundamental in order to both uncover the elusive progenitors of SLSNe and to study star formation in dwarf galaxies. In this paper, we present the first results of our project to study SUperluminous Supernova Host galaxIES, focusing on the sample for which we have obtained spectroscopy. We show that SLSNe-I and SLSNe-R (hydrogen-poor) often (˜50 per cent in our sample) occur in a class of galaxies that is known as Extreme Emission Line Galaxies (EELGs). The probability of this happening by chance is negligible and we therefore conclude that the extreme environmental conditions and the SLSN phenomenon are related. In contrast, SLSNe-II (hydrogen-rich) occur in more massive, more metal-rich galaxies with softer radiation fields. Therefore, if SLSNe-II constitute a uniform class, their progenitor systems are likely different from those of H-poor SLSNe. Gamma-ray bursts (GRBs) are, on average, not found in as extreme environments as H-poor SLSNe. We propose that H-poor SLSNe result from the very first stars exploding in a starburst, even earlier than GRBs. This might indicate a bottom-light initial mass function in these systems. SLSNe present a novel method of selecting candidate EELGs independent of their luminosity