Early gray dust formation in the type IIn SN 2005ip

The physical characteristics of dust formed in supernovae is poorly known. In this paper, we investigate the extinction properties of dust formed in the type IIn SN 2005ip. The observed light curves of SN 2005ip all exhibit a sudden drop around 50 days after discovery. This has been attributed to dust formation in the dense circumstellar medium. We modeled the intrinsic light curves in six optical bands, adopting a theoretical model for the luminosity evolution of supernovae interacting with their circumstellar material. From the difference between the observed and intrinsic light curves, we calculated extinction curves as a function of time. The total-to-selective extinction ratio, $R_V$, was determined from the extinction in the B and V bands. The resulting extinction, $A_V$, increases monotonically up to about 1 mag, 150 days after discovery. The inferred $R_V$ value also increases slightly with time, but appears constant in the range 4.5--8, beyond 100 days after discovery. The analysis confirms that dust is likely formed in SN 2005ip, starting about two months after explosion. The high value of $R_V$, that is, gray dust, suggests dust properties different from of the Milky Way. While this result hinges on the assumed theoretical intrinsic light curve evolution, it is encouraging that the fitted light curves are as expected for standard ejecta and circumstellar medium density structures.Comment: Accepted for publication in A&

The Opacity of Spiral Galaxy Disks VI: Extinction, stellar light and color

In this paper we explore the relation between dust extinction and stellar light distribution in disks of spiral galaxies. Extinction influences our dynamical and photometric perception of disks, since it can distort our measurement of the contribution of the stellar component. To characterize the total extinction by a foreground disk, Gonzalez et al. (1998) proposed the ``Synthetic Field Method'' (SFM), which uses the calibrated number of distant galaxies seen through the foreground disk as a direct indication of extinction. The method is described in Gonzalez et al. (1998) and Holwerda et al. (2005a). To obtain good statistics, the method was applied to a set of HST/WFPC2 fields Holwerda et al. (2005b) and radial extinction profiles were derived, based on these counts. In the present paper, we explore the relation of opacity with surface brightness or color from 2MASS images, as well as the relation between the scalelengths for extinction and light in the I band. We find that there is indeed a relation between the opacity (A_I) and the surface brightness, particularly at the higher surface brightnesses. No strong relation between near infrared (H-J, H-K) color and opacity is found. The scalelengths of the extinction are uncertain for individual galaxies but seem to indicate that the dust distribution is much more extended than the stellar light. The results from the distant galaxy counts are also compared to the reddening derived from the Cepheids light-curves Freedman et al. (2001). The extinction values are consistent, provided the selection effect against Cepheids with higher values of A_I is taken into account. The implications from these relations for disk photometry, M/L conversion and galaxy dynamical modeling are briefly discussed.Comment: 9 pages, 2 tables, 10 figures, accepted by A&

The peculiar extinction law of SN2014J measured with The Hubble Space Telescope

The wavelength-dependence of the extinction of Type Ia SN2014J in the nearby galaxy M82 has been measured using UV to near-IR photometry obtained with the Hubble Space Telescope, the Nordic Optical Telescope, and the Mount Abu Infrared Telescope. This is the first time that the reddening of a SN Ia is characterized over the full wavelength range of $0.2$-$2$ microns. A total-to-selective extinction, $R_V\geq3.1$, is ruled out with high significance. The best fit at maximum using a Galactic type extinction law yields $R_V = 1.4\pm0.1$. The observed reddening of SN2014J is also compatible with a power-law extinction, $A_{\lambda}/A_V = \left( {\lambda}/ {\lambda_V} \right)^{p}$ as expected from multiple scattering of light, with $p=-2.1\pm0.1$. After correction for differences in reddening, SN2014J appears to be very similar to SN2011fe over the 14 broad-band filter light curves used in our study.Comment: Accepted for publication in ApJ

UVOT Measurements of Dust and Star Formation in the SMC and M33

When measuring star formation rates using ultraviolet light, correcting for dust extinction is a critical step. However, with the variety of dust extinction curves to choose from, the extinction correction is quite uncertain. Here, we use Swift/UVOT to measure the extinction curve for star-forming regions in the SMC and M33. We find that both the slope of the curve and the strength of the 2175 Angstrom bump vary across both galaxies. In addition, as part of our modeling, we derive a detailed recent star formation history for each galaxy.Comment: 6 pages, 5 figures, conference proceedings from Swift: 10 years of Discovery, held in Rome (2-5 Dec. 2014

How the extinction of extragalactic background light affects surface photometry of galaxies, groups and clusters

The faint regions of galaxies, groups and clusters hold important clues about how these objects formed, and surface photometry at optical and near-infrared wavelengths represents a powerful tool for studying such structures. Here, we identify a hitherto unrecognized problem with this technique, related to how the night sky flux is typically measured and subtracted from astronomical images. While most of the sky flux comes from regions between the observer and the target object, a small fraction - the extragalactic background light (EBL) - comes from behind. We argue that since this part of the sky flux can be subject to extinction by dust present in the galaxy/group/cluster studied, standard reduction procedures may lead to a systematic oversubtraction of the EBL. Even very small amounts of extinction can lead to spurious features in radial surface surface brightness profiles and colour maps of extended objects. We assess the likely impact of this effect on a number of topics in extragalactic astronomy where very deep surface photometry is currently attempted, including studies of stellar halos, starburst host galaxies, disc truncations and diffuse intragroup/intracluster light. We argue that EBL extinction may provide at least a partial explanation for the anomalously red colours reported for the halos of disc galaxies and the hosts of local starburst galaxies. EBL extinction effects also mimic truncations in discs with unusually high dust opacities, but are unlikely to be the cause of such features in general. Failure to account for EBL extinction can also give rise to a non-negligible underestimate of intragroup and intracluster light at the faintest surface brightness levels currently probed. (Abridged)Comment: 15 pages, 10 figures, accepted for publication in MNRA

Initial investigation of the wavelength dependence of optical properties measured with a new multi-pass Aerosol Extinction Differential Optical Absorption Spectrometer (AE-DOAS)

Atmospheric aerosols directly affect climate by scattering and absorbing radiation. The magnitude of the impact is dependent upon the wavelength of light, but is often estimated near 550 nm. When light scattering and absorption by aerosols is approximated, the wavelength dependence of the refractive index for specific components is lost. As a result, climate models would have inherent uncertainties for aerosol contributions to radiative forcing when considering the entire solar spectrum. An aerosol extinction differential optical absorption spectrometer has been developed to directly measure aerosol extinction at mid-ultraviolet to near infrared wavelengths. The instrument consists of a spectrometer coupled to a closed White-type multi-pass gas cell with an adjustable path length of up to approximately 20 m. Laboratory measurements of various gases are compared with known absorption cross sections. Additionally, the extinction of monodisperse samples of polystyrene latex spheres are measured and compared to Mie theory generated with refractive index values from the literature to validate the new instrument. The polystyrene experiments also emphasize the ability of the new instrument to retrieve the wavelength dependent refractive index, especially in the ultraviolet wavelength regions where variability is expected. The spectrometer will be a significant advancement for determining wavelength dependent complex refractive indices in future laboratory studies as well as provide the ability to monitor ambient aerosol light extinction

Magneto-electric point scattering theory for metamaterial scatterers

We present a new, fully analytical point scattering model which can be applied to arbitrary anisotropic magneto-electric dipole scatterers, including split ring resonators (SRRs), chiral and anisotropic plasmonic scatterers. We have taken proper account of reciprocity and radiation damping for electric and magnetic scatterers with any general polarizability tensor. Specifically, we show how reciprocity and energy balance puts constraints on the electrodynamic responses arbitrary scatterers can have to light. Our theory sheds new light on the magnitude of cross sections for scattering and extinction, and for instance on the emergence of structural chirality in the optical response of geometrically non-chiral scatterers like SRRs. We apply the model to SRRs and discuss how to extract individual components of the polarizability matrix and extinction cross sections. Finally, we show that our model describes well the extinction of stereo-dimers of split rings, while providing new insights in the underlying coupling mechanisms.Comment: 12 pages, 3 figure

Infrared light extinction by charged dielectric core-coat particles

We study the effect of surplus electrons on the infrared extinction of dielectric particles with a core-coat structure and propose to use it for an optical measurement of the particle charge in a dusty plasma. The particles consist of an inner core with negative and an outer coat with positive electron affinity. Both the core and the coat give rise to strong transverse optical phonon resonances, leading to anomalous light scattering in the infrared. Due to the radial profile of the electron affinity electrons accumulate in the coat region making the infrared extinction of this type of particles very charge-sensitive, in particular, the extinction due to a resonance arising solely due to the core-coat structure. The maximum of this resonance is in the far-infrared and responds to particle charges realizable in ordinary dusty laboratory plasmas.Comment: 12 pages, 8 figure