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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.
| GPM - compiled catalogue of absolute proper motions of stars in selected areas of sky with galaxies.
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| GPM1 - a catalog of absolute proper motions of stars with respect to galaxies
The description of the first version of the General Compiled Catalogueof Absolute Proper Motions (GPM1) for a sample of HIPPARCOS stars,derived with respect to galaxies within the plan called Catalogue ofFaint Stars (KSZ, Deutch 1952), is presented. The principal aim of theGPM1 construction was to provide absolute proper motions of stars todetermine the rotation of the HIPPARCOS system. The GPM1 cataloguecontains 977 HIPPARCOS Input Catalogue stars with V magnitudes $5^m -11^m in 180 fields north of -25 degrees of declination. The accuracy ofthe proper motions is 8 mas/yr (milliarcseconds per year). Comparison ofproper motions of GPM1 with those of the PPM and ACRS was performed andanalyzed with respect to systematic errors caused by spurious rotationof the FK5 system. The standard errors show that the rotation may bedetermined with an accuracy better than 1 mas/yr. Catalog is onlyavailable in electronic form at the CDS via anonymous ftpcdsarc.u-strasbg.fr or ftp 130.79.128.5.
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