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Spectropolarimetry of the Peculiar Type Ia Supernova 2005hk
We present Keck spectropolarimetry of the unusual Type Ia supernova (SNIa) 2005hk several days before maximum light. An analysis of the highsignal-to-noise ratio total-flux spectrum shows the object's extremesimilarity to the peculiar SN 2002cx. SN 2005hk has an optical spectrumdominated by Fe III lines and only weak lines of intermediate-masselements, unlike a normal SN Ia at this epoch. The photospheric velocitymeasured from the minima of strong absorption lines is very low for anSN Ia (~6000 km s-1), solidifying the connection to SN2002cx. The spectrum-synthesis code SYNOW was used to identify thepresence of iron-peak elements, intermediate-mass elements, and possiblyunburned carbon at similar velocities in the outer ejecta of SN 2005hk.Many weak spectral features remain unidentified. The spectropolarimetryshows a low level of continuum polarization (~0.4%) after correction forthe interstellar component, and only a weak Fe III line feature isdetected. The level of continuum polarization is normal for an SN Ia,implying that the unusual features of SN 2005hk cannot be readilyexplained by large asymmetries.
| Evidence for Spectropolarimetric Diversity in Type Ia Supernovae
We present single-epoch, postmaximum spectropolarimetry of four Type Iasupernovae (SNe Ia) that span a range of spectral and photometricproperties: SN 2002bf and SN 2004dt exhibit unusually high-velocity (HV)absorption lines. SN 1997dt is probably somewhat subluminous, and SN2003du is slightly overluminous. We detect polarization modulationsacross strong lines in all four objects, demonstrating that all areintrinsically polarized. However, the nature and degree of thepolarization varies considerably. Including all SNe Ia studied thus far,the following order emerges in terms of increasing strength ofline-polarization features: ordinary/overluminous
| Photospheric-Phase Spectropolarimetry and Nebular-Phase Spectroscopy of the Peculiar Type Ic Supernova 2002ap
The early-time optical spectrum of the Type Ic supernova (SN) 2002ap wascharacterized by unusually broad features, leading some authors todesignate it a ``hypernova.'' We present optical spectropolarimetry ofthis object 16 and 37 days after the estimated date of explosion. Aftercorrecting for interstellar polarization, we find evidence for a highlevel of intrinsic continuum polarization at both epochs: p>~1.3% onday 16 and p>~1.0% on day 37. Prominent line polarization is alsoseen, especially in the trough of the Ca II near-infrared triplet duringthe second epoch. When interpreted in terms of the oblate,electron-scattering model atmospheres of Höflich, our results implyan asymmetry of at least 20% (day 16) and 17% (day 37). The data suggesta fair degree of axisymmetry, although the polarization angle of thedominant polarization axes are different by about 55° between thetwo epochs, implying a complex morphology for the thinning ejecta. Inparticular, there exists some spectropolarimetric evidence for adifferent distribution of Ca relative to iron-group elements. We alsopresent flux spectra of SN 2002ap taken 131 and 140 days after theexplosion. The spectra are characterized by a very weak continuum andbroad emission lines, indicating that SN 2002ap has entered the nebularphase. The spectral features are substantially similar to those of``normal'' SNe Ic in the nebular phase, and the emission lines are notsignificantly broader. However, some of the broad lines are very sharplypeaked and may possess a narrow component (probably unresolved by ourspectra, FWHM<~400 km s-1) that is redshifted by ~580 kms-1 with respect to the systemic velocity of the hostgalaxy.
| Evidence for Extremely High Dust Polarization Efficiency in NGC 3184
Recent studies have found the Type II-plateau supernova (SN) 1999gi tobe highly polarized (pmax=5.8%, where pmax is thehighest degree of polarization measured in the optical bandpass) andminimally reddened [E(B-V)=0.21+/-0.09 mag]. From multiple lines ofevidence, including the convincing fit of a ``Serkowski'' interstellarpolarization (ISP) curve to the continuum polarization shape, weconclude that the bulk of the observed polarization is likely due todust along the line of sight and is not intrinsic to SN 1999gi. Wepresent new spectropolarimetric observations of four distant Galacticstars close to the line of sight to SN 1999gi (two are within 0.02d) andfind that all are null to within 0.2%, effectively eliminating Galacticdust as the cause of the high polarization. The high ISP coupled withthe low reddening implies an extraordinarily high polarizationefficiency for the dust along this line of sight in NGC 3184:ISP/E(B-V)=31+22-9% mag -1. This isinconsistent with the empirical Galactic limit [ISP/E(B-V)<9%mag-1] and represents the highest polarization efficiency yetconfirmed for a single sight line in either the Milky Way or an externalgalaxy.
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Наблюдательные данные и астрометрия
| Созвездие: | Близнецы |
| Прямое восхождение: | 07h23m24.60s |
| Склонение: | +25°30'58.5" |
| Видимая звёздная величина: | 8.877 |
| Собственное движение RA: | -2.2 |
| Собственное движение Dec: | -3.1 |
| B-T magnitude: | 8.826 |
| V-T magnitude: | 8.873 |
Каталоги и обозначения:
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