We establish correlations between equivalent widths of eight diffuse interstellar bands (DIBs), and examine their correlations with atomic hydrogen, molecular hydrogen, and E B−V . The DIBs are centered at λλ 5780. 5, 6204.5, 6283.8, 6196.0, 6613.6, 5705.1, 5797.1, and 5487.7, in decreasing order of Pearson's correlation coefficient with N(H) (here defined as the column density of neutral hydrogen), ranging from 0.96 to 0.82. We find the equivalent width of λ5780.5 is better correlated with column densities of H than with E B−V or H 2 , confirming earlier results based on smaller datasets. We show the same is true for six of the seven other DIBs presented here. Despite this similarity, the eight strong DIBs chosen are not well enough correlated with each other to suggest they come from the same carrier. We further conclude that these eight DIBs are more likely to be associated with H than with H 2 , and hence are not preferentially located in the densest, most UV shielded parts of interstellar clouds. We suggest they arise from different molecules found in diffuse H regions with very little H 2 (molecular

We present optical photometric and spectroscopic observations of supernova 2013ej. It is one of the brightest type II supernovae exploded in a nearby (∼ 10 Mpc) galaxy NGC 628. The light curve characteristics are similar to type II SNe, but with a relatively shorter (∼ 85 day) and steeper (∼ 1.7 mag (100 d) −1 in V ) plateau phase. The SN shows a large drop of 2.4 mag in V band brightness during plateau to nebular transition. The absolute ultraviolet (UV) light curves are identical to SN 2012aw, showing a similar UV plateau trend extending up to 85 days. The radioactive 56 Ni mass estimated from the tail luminosity is 0.02M ⊙ which is significantly lower than typical type IIP SNe. The characteristics of spectral features and evolution of line velocities indicate that SN 2013ej is a type II event. However, light curve characteristics and some spectroscopic features provide strong support in classifying it as a type IIL event. A detailed synow modelling of spectra indicates the presence of some high velocity components in Hα and Hβ profiles, implying possible ejecta-CSM interaction. The nebular phase spectrum shows an unusual notch in the Hα emission which may indicate bipolar distribution of 56 Ni. Modelling of the bolometric light curve yields a progenitor mass of ∼ 14M ⊙ and a radius of ∼ 450R ⊙ , with a total explosion energy of ∼ 2.3 × 10 51 erg.

Absorption spectra toward Herschel 36 for theà 1 Π ←X 1 Σ transitions of CH + in the J = 1 excited rotational level and theà 2 ∆ ←X 2 Π transition of CH in the J = 3/2 excited fine structure level have been analyzed. These excited levels are above their ground levels by 40.1 K and ∼ 25.7 K and indicate high radiative temperatures of the environment, 14.6 K and 6.7 K, respectively. The effect of the high radiative temperature is more spectacular in some diffuse interstellar bands (DIBs) observed toward Her 36; remarkable extended tails toward red (ETR) were observed. We interpret these ETRs as due to a small decrease of rotational constants upon excitation of the excited electronic states. Along with radiative pumping of a great many high-J rotational levels, this causes the ETRs. In order to study this effect quantitatively, we have developed a model calculation in which the effects of collision and radiation are treated simultaneously. The simplest case of linear molecules is considered. It has been found that the ETR is reproduced if the fraction of the variation of the rotational constant, β ≡ (B ′ − B)/B, is sufficiently high (3 − 5%) and the radiative temperature is high (T r > 50 K).Although modeling for general molecules is beyond the scope of this paper, the results indicate that the prototypical DIBs λ5780.5, λ5797.1, and λ6613.6 which show the pronounced ETRs are due to polar molecules sensitive to the radiative excitation. The requirement of high β favors relatively small molecules with 3-6 heavy atoms. DIBs λ5849.8, λ6196.0, and λ6379.3 which do not show the pronounced ETRs are likely due to non-polar molecules or large polar molecules with small β.

Aiming for a new and more comprehensive DIB catalog between 4,000 and 9,000Å, we revisited the Atlas Catalog based on the observations of HD 183143 and HD 204827 (Hobbs et al. 2008 and). Twenty-five medium-to-highly reddened sight lines were selected, sampling a variety of spectral types of the background star and the interstellar environments. The median SNR of these spectra is ~ 1,300 around 6,400Å. Compared to the Atlas Catalog, 22 new DIBs were found, and the boundaries of 27 (sets) of DIBs were adjusted, resulting in an updated catalog containing 559 DIBs that we refer to as the Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands. Measurements were then made based on this catalog. We found our survey most sensitive between 5,500 and 7,000Å due largely to the local SNR of the spectra, the relative absence of interfering stellar lines, and the weakness of telluric residuals. For our data sample, the number of DIBs detected in a given sight line is mostly dependent on E B-V and less on the spectral type of the background star. Some dependence on f H2 is observed, but less well-determined due to the limited size of the data sample. The variations of the wavelengths of each DIB in different sight lines are generally larger than those of the known interstellar lines CH + , CH, and K I.Those variations could be due to the inherent error in the measurement, or to differences in the velocity components among sight lines.

We discuss the absorption due to various constituents of the interstellar medium of M82 seen in moderately high resolution, high signal-to-noise ratio optical spectra of SN 2014J. Complex absorption from M82 is seen, at velocities 45 v LSR 260 km s −1 , for Na I, K I, Ca I, Ca II, CH, CH + , and CN; many of the diffuse interstellar bands (DIBs) are also detected. Comparisons of the column densities of the atomic and molecular species and the equivalent widths of the DIBs reveal both similarities and differences in relative abundances, compared to trends seen in the ISM of our Galaxy and the Magellanic Clouds. Of the ten relatively strong DIBs considered here, six (including λ5780.5) have strengths within ±20% of the mean values seen in the local Galactic ISM, for comparable N (K I); two are weaker by 20-45% and two (including λ5797.1) are stronger by 25-40%. Weaker than "expected" DIBs [relative to N (K I), N (Na I), and E(B − V )] in some Galactic sight lines and toward several other extragalactic supernovae appear to be associated with strong CN absorption and/or significant molecular fractions. While the N (CH)/N (K I) and N (CN)/N (CH) ratios seen toward SN 2014J are similar to those found in the local Galactic ISM, the combination of high N (CH + )/N (CH) and high W (5797.1)/W (5780.5) ratios has not been seen elsewhere. The centroids of many of the M82 DIBs are shifted, relative to the envelope of the K I profile -likely due to component-to-component variations in W (DIB)/N (K I) that may reflect the molecular content of the individual components. We compare estimates for the host galaxy reddening E(B − V ) and visual extinction A V derived from the various interstellar species with the values estimated from optical and near-IR photometry of SN 2014J.

Abstract:We study the behavior of eight diffuse interstellar bands (DIBs) in different interstellar environments, as characterized by the fraction of hydrogen in molecular form (f H2 ), with comparisons to the corresponding behavior of various known atomic and molecular species. The equivalent widths of the five "normal" DIBs (ll5780.5, 5797.1, 6196.0, 6283.8, and 6613.6), normalized to E B-V , show a "Lambda-shaped" behavior: they increase at low f H2 , peak at f H2 ~ 0.3, and then decrease. The similarly normalized column densities of Ca, Ca + , Ti + , and CH + also decline for f H2 > 0.3. In contrast, the normalized column densities of Na, K, CH, CN, and CO increase monotonically with f H2 , and the trends exhibited by the three C 2 DIBs (ll4726.8, 4963.9, and 4984.8) lie between those two general behaviors. These trends with f H2 are accompanied by cosmic scatter, the dispersion at any given f H2 being significantly larger than the individual errors of measurement. The Lambda-shaped trends suggest the balance between creation and destruction of the DIB carriers differs dramatically between diffuse atomic and diffuse molecular clouds; additional processes besides ionization and shielding are needed to explain those observed trends. Except for several special cases, the highest W l (5780)/W l (5797) ratios, characterizing the so-called "sigma-zeta effect", occur only at f H2 < 0.2. We propose a sequence of DIBs based on trends in their pair-wise strength ratios with increasing f H2 . In order of increasing environmental density, we find the l6283.8 and l5780.5 DIBs, the l6196.0 DIB, the l6613.6 DIB, the l5797.1 DIB, and the C 2 DIBs.

We present a comprehensive analysis of interstellar absorption lines seen in moderately-high resolution, high signal-to-noise ratio optical spectra of SN 2014J in M82. Our observations were acquired over the course of six nights, covering the period from ∼6 days before to ∼30 days after the supernova reached its maximum B-band brightness. We examine complex absorption from Na i, Ca ii, K i, Ca i, CH + , CH, and CN, arising primarily from diffuse gas in the interstellar medium (ISM) of M82. We detect Li i absorption over a range in velocity consistent with that exhibited by the strongest Na i and K i components associated with M82; this is the first detection of interstellar Li in a galaxy outside of the Local Group. There are no significant temporal variations in the absorption-line profiles over the 37 days sampled by our observations. The relative abundances of the various interstellar species detected reveal that the ISM of M82 probed by SN 2014J consists of a mixture of diffuse atomic and molecular clouds characterized by a wide range of physical/environmental conditions. Decreasing N (Na i)/N (Ca ii) ratios and increasing N (Ca i)/N (K i) ratios with increasing velocity are indicative of reduced depletion in the higher-velocity material. Significant component-to-component scatter in the N (Na i)/N (Ca ii) and N (Ca i)/N (Ca ii) ratios may be due to variations in the local ionization conditions. An apparent anti-correlation between the N (CH + )/N (CH) and N (Ca i)/N (Ca ii) ratios can be understood in terms of an opposite dependence on gas density and radiation field strength, while the overall high CH + abundance may be indicative of enhanced turbulence in the ISM of M82. The Li abundance also seems to be enhanced in M82, which supports the conclusions of recent gamma-ray emission studies that the cosmic-ray acceleration processes are greatly enhanced in this starburst galaxy.

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