Showing papers by "Dominion Astrophysical Observatory published in 2010"

Discovery of the Extremely Energetic Supernova 2008fz

Abstract: We report on the discovery and initial observations of the energetic type IIn supernova 2008fz. This object was discovered at redshift z = 0.133 and reached an apparent magnitude of V ~ 17. After correcting for Galactic extinction and redshift, we determine the peak absolute magnitude of the event to be M_V = –22.3, placing it among the most luminous supernovae discovered. The optical energy emitted by SN 2008fz (based on the light curve over an 88 day period) is possibly the most ever observed for a supernova (>1.4 × 10^(51) erg). The event was more luminous than the type IIn SN 2006gy, but exhibited the same smooth, slowly evolving light curve. As is characteristic of type IIn supernova, the early spectra of SN 2008fz initially exhibited narrow Balmer lines which were replaced by a broader component at later times. The spectra also show a blue continuum with no signs of Ca or Na absorption, suggesting that there is little extinction due to dust in the host or circumstellar material. No host galaxy is identified in prior co-added images reaching R ~ 22. From the supernova's redshift, we place an upper limit on the brightness of the host of M_R ~ –17 (similar to the brightness of the Small Magellanic Cloud). The presence of the supernova within such a faint galaxy follows the majority of recently discovered highly luminous supernovae. A possible reason for this is the combination of a high star formation rate in low-mass galaxies with a low-metallicity environment.

Mixed-morphology supernova remnants in x-rays: isothermal plasma in hb21 and probable oxygen-rich ejecta in ctb 1

Abstract: We present an analysis of X-ray observations of the Galactic supernova remnants (SNRs) HB21 (G89.0+4.7) and CTB 1 (G116.9+0.2), two well-known members of the class of mixed-morphology (MM) SNRs. Our analysis draws upon observations of both SNRs made with the Advanced Satellite for Cosmology and Astrophysics (ASCA): we have also used an archived Chandra observation of CTB 1 as part of this effort. We find a marked contrast between the X-ray properties of HB21 and CTB 1: in the case of HB21, the extracted spectra of the northwest and southeast regions of the X-ray-emitting plasma associated with the SNR can be fit with a single thermal model with marginally enhanced silicon and sulfur abundances. For both of these regions, the derived column density and temperature are N_H ~ 0.3 × 10^(22) cm^(−2) and kT ~ 0.7 keV, respectively. No significant spatial differences in temperature or elemental abundances between the two regions are detected and the X-ray-emitting plasma for both regions is close to ionization equilibrium. Our Chandra spectral analysis of CTB 1 reveals that this source is likely an oxygen-rich SNR with enhanced abundances of oxygen and neon: this result is quite surprising for an evolved SNR like CTB 1. The high angular resolution Chandra observation of CTB 1 reveals spectral variations across this SNR: in particular, we have detected localized hard emission with an angular extent of ~1'. The extracted ASCA spectra for both the southwest and northeastern regions of CTB 1 cannot be fit with a single thermal component and instead an additional component is required to account for the presence of excess emission seen at higher energies. Based on our fits to the extracted ASCA spectra, we derive a column density NH ~ 0.6 × 10^(22) cm^(−2) and a temperature for the soft thermal component of kT_(soft) ~ 0.28 keV for both regions. The hard emission from the southwest region may be modeled with either a thermal component with a temperature kT_(hard) ~ 3 keV or by a power-law component with a photon index Γ ~ 2–3; for the northeast region, the hard emission may be modeled with a power-law component with a photon index Γ = 1.4. The detection of center-filled ejecta-dominated X-ray emission from HB21 and CTB 1 as well as other MM SNRs suggests a new scenario for the origin of the contrasting X-ray and radio morphologies of this class of sources. Lastly, we have analyzed the properties of the discrete hard X-ray source 1WGA J0001.4+6229 which is seen in projection just inside the northeastern shell of CTB 1. Our extracted ASCA GIS spectra of this source are best fit using a power-law model with a photon index Γ = 2.2^(+0.5)_(−1.2): this slope is typical for featureless power-law continua produced by rotation-powered pulsars. This source may be a neutron star associated with CTB 1. We find marginal evidence for X-ray pulsations from this source with a period of 47.6154 ms. A deep radio observation of this source failed to reveal any pulsations.

Mixed-Morphology Supernova Remnants in X-rays: Isothermal Plasma in HB21 and Probable Oxygen-Rich Ejecta in CTB 1

Abstract: (Abridged) We present an analysis of X-ray observations made of the Galactic supernova remnants (SNRs) HB21 (G89.0+4.7) and CTB 1 (G116.9+0.2), two well-known mixed-morphology (MM) SNRs. We find a marked contrast between the X-ray properties of these SNRs: for HB21, the extracted ASCA spectra of the northwest and southeast regions of the X-ray emitting plasma can be fit with a single thermal model with marginally enhanced silicon and sulfur abundances. For both of these regions, the derived column density and temperature are N_H~0.3x10^22 cm^-2 and kT~0.7 keV, respectively. No significant spatial differences in temperature or elemental abundances between the two regions are detected and the X-ray-emitting plasma in both regions is close to ionization equilibrium. Our Chandra spectral analysis of CTB 1 reveals that this source is likely an oxygen-rich SNR with enhanced abundances of oxygen and neon. The extracted ASCA spectra for the southwestern and northeastern regions of CTB 1 cannot be fit with a single thermal component. Based on our fits to these spectra, we derive a column density N_H~0.6x10^22 cm^-2 and a temperature for the soft thermal component of kT_soft~0.28 keV. The hard emission from the southwest may be modeled with either a thermal component (kT_hard~3 keV) or by a power law component (Gamma~2-3) while the hard emission from the northeast may be modeled with a power law component (Gamma~1.4). We have also extracted ASCA GIS spectra of the discrete X-ray source 1WGA J0001.4+6229 which is seen in projection toward CTB 1. These spectra are best fit using a power-law model with a photon index Gamma=2.2^{+0.5}_{-1.2} which is typical for featureless power-law continua produced by rotation-powered pulsars. This source may be a neutron star associated with CTB 1.

The infrared imaging spectrograph (IRIS) for TMT: imager design

Abstract: We describe an optical design of an imager mode of the IRIS instrument for the Thirty Meter Telescope IRIS is a fully-cryogenic diffraction-limited infrared camera and integral field spectrograph working in the wavelength coverage from 084 to 24 microns The imager mode covers 164" × 164" FOV with a 4096 × 4096 detector array with sampling 4 milli-arcsec/pix There are two challenges in performance which the science cases require in the imager mode 1) rms wavefront error should be less than 30 nm, and 2) optical distortion should be corrected sufficiently to achieve astrometric accuracy of 10 micro-arcsec Among possible optical configurations consisting of reflective and refractive solutions, a refractive solution with apochromatic triplets best meets the requirements The optical system consists of a collimator and camera both of which have a BaF2-Fused Silica- ZnSe apochromatic triplet and a single BaF2 lens near the focus The rms wavefront error of the system including the telescope, adaptive optics, and imager mode is less than 22 nm with ideal optical parameters A sensitivity analysis shows that reasonable amount of errors in fabrication and alignment will give the rms wavefront error of less than 30 nm in 90 % of all cases We also investigate accuracy of the distortion correction and how movable parts affect the correction accuracy We find that uncorrectable distortion correction errors are well below 10 micro-arcsec with reasonable stability and repeatability of the movable parts

Spectral Type and Radial Velocity Variations in Three SRC Variables

Abstract: SRC variables are M supergiants, precursors to Type II supernovae, that vary in brightness with moderately regular periods of order 100–1000 days. Although identified as pulsating stars that obey their own period-luminosity relation, few have been examined in enough detail to follow the temperature and spectral changes that they undergo during their long cycles. The present study examines such changes for several SRC variables revealed by CCD spectra obtained at the Dominion Astrophysical Observatory (DAO) during 2005–2009, as well as by archival spectra from the DAO (and elsewhere) for some stars from the 1960s to 1980s, and Cambridge radial velocity spectrometer measures for Betelgeuse. Described here is our classification procedure and information on the spectral type and radial velocity changes in three of the stars. The results provide insights into the pulsation mechanism in M supergiants.