Constraining the Age and Distance of the Galactic Supernova Remnant G156.2+5.7 by H-alpha Expansion Measurements

We present deep H-alpha images of portions of the X-ray bright but optically faint Galactic supernova remnant G156.2+5.7, revealing numerous and delicately thin nonradiative filaments which mark the location of the remnant's forward shock. These new images show that these filaments have a complex structure not visible on previous lower resolution optical images. By comparing H-alpha images taken in 2004 at the McDonald Observatory and in 2015-2016 at the Kiso Observatory, we set a stringent 1-sigma upper limit of expansion to be 0.06 arcsec/yr. This proper motion, combined with a shock speed of 500 km/s inferred from X-ray spectral analyses, gives a distance of > 1.7 kpc. In addition, a simple comparison of expansion indices of several SNRs allows us to infer the age of the remnant to be a few 10,000 yr old. These estimates are more straightforward and reliable than any other previous studies, and clearly rule out a possibility that G156.2+5.7 is physically associated with part of the Taurus-Auriga cloud and dust complex at a distance of 200-300 pc.Comment: 16 pages, 5 figures, accepted for publication in The Astrophysical Journa

Delay Time Distribution Measurement of Type Ia Supernovae by the Subaru/XMM-Newton Deep Survey and Implications for the Progenitor

The delay time distribution (DTD) of type Ia supernovae (SNe Ia) from star formation is an important clue to reveal the still unknown progenitor system of SNe Ia. Here we report on a measurement of the SN Ia DTD in a delay time range of t_Ia = 0.1-8.0 Gyr by using the faint variable objects detected in the Subaru/XMM-Newton Deep Survey (SXDS) down to i' ~ 25.5. We select 65 SN candidates showing significant spatial offset from nuclei of the host galaxies having old stellar population at z ~ 0.4-1.2, out of more than 1,000 SXDS variable objects. Although spectroscopic type classification is not available for these, we quantitatively demonstrate that more than ~80% of these should be SNe Ia. The DTD is derived using the stellar age estimates of the old galaxies based on 9 band photometries from optical to mid-infrared wavelength. Combined with the observed SN Ia rate in elliptical galaxies at the local universe, the DTD in t_Ia ~ 0.1-10 Gyr is well described by a featureless power-law as f_D(t_Ia) \propto t_Ia^{-1}. The derived DTD is in excellent agreement with the generic prediction of the double-degenerate scenario, giving a strong support to this scenario. In the single-degenerate (SD) scenario, although predictions by simple analytic formulations have broad DTD shapes that are similar to the observation, DTD shapes calculated by more detailed binary population synthesis tend to have strong peaks at characteristic time scales, which do not fit the observation. This result thus indicates either that the SD channel is not the major contributor to SNe Ia in old stellar population, or that improvement of binary population synthesis theory is required. Various sources of systematic uncertainties are examined and tested, but our main conclusions are not affected significantly.Comment: Matches the final version to be published in PASJ. A very minor bug in the visibility time calculation has been fixed, resulting in slight changes in the derived DTD (<~ 10%). Conclusions are not affected at all. The font error of the labels in Fig 3 also fixe

Proper motions with Subaru II. A sample in the Subaru/XMM-Newton Deep Survey field

We search for stars with proper motions in a set of deep Subaru images, covering about 0.48 square degrees to a depth of $i' \simeq 26$, taken over a span of five and a half years. We follow the methods described in \citet{Richmond2009} to reduce and analyze this dataset. We present a sample of 69 stars with motions of high significance, and discuss briefly the populations from which they are likely drawn. Based on photometry and motions alone, we expect that 14 of the candidates may be white dwarfs. Our candidate with the largest proper motion is surprisingly faint and likely to prove interesting: its colors and motions suggest that it might be an M dwarf moving at over 500 km/sec or an L dwarf in the halo.Comment: 10 pages, 5 figures. Accepted by Publications of the Astronomical Society of Japan, to appear in volume 62, February 2010. Revised version: removed PASJ LaTeX tutorial which was mistakenly appended to pape

Proper motions with Subaru I. Methods and a first sample in the Subaru Deep Field

We search for stars with proper motions in a set of twenty deep Subaru images, covering about 0.28 square degrees to a depth of i ~ 25, taken over a span of six years. In this paper, we describe in detail our reduction and techniques to identify moving objects. We present a first sample of 99 stars with motions of high significance, and discuss briefly the populations from which they are likely drawn. Based on photometry and motions alone, we expect that 9 of the candidates may be white dwarfs. We also find a group of stars which may be extremely metal-poor subdwarfs in the halo.Comment: 12 pages, 8 figures, submitted to PAS

Constraining the Age and Distance of the Galactic Supernova Remnant G156.2+5.7 by H A Expansion Measurements

We present deep Hα images of portions of the X-ray bright, but optically faint, Galactic supernova remnant G156.2+5.7, revealing numerous and delicately thin non-radiative filaments, which mark the location of the remnant\u27s forward shock. These new images show that these filaments have a complex structure not visible on previous lower resolution optical images. By comparing Hα images taken in 2004 at the McDonald Observatory and in 2015–2016 at the Kiso Observatory, we set a stringent 1σ upper limit of expansion to be 0.06 arcsec/yr. This proper motion, combined with a shock speed of 500 km s−1, inferred from X-ray spectral analyses, gives a distance of \u3e 1.7 kpc. In addition, a simple comparison of expansion indices of several supernova remnants allows us to infer the age of the remnant to be a few tens of thousands years old. These estimates are more straightforward and reliable than any other previous studies, and clearly rule out the possibility that G156.2+5.7 is physically associated with part of the Taurus–Auriga cloud and dust complex at a distance of 200–300 pc

The Subaru/XMM-Newton Deep Survey (SXDS) - V. Optically Faint Variable Object Survey

We present our survey for optically faint variable objects using multi-epoch (8−10 epochs over 2−4 years) i′-band imaging data obtained with Subaru Suprime-Cam over 0.918 deg2 in the Subaru/XMMNewton Deep Field (SXDF). We found 1040 optically variable objects by image subtraction for all the combinations of images at different epochs. This is the first statistical sample of variable objects at depths achieved with 8-10m class telescopes or HST. The detection limit for variable components is i′ vari 25.5 mag. These variable objects were classified into variable stars, supernovae (SNe), and active galactic nuclei (AGN), based on the optical morphologies, magnitudes, colors, and opticalmid- infrared colors of the host objects, spatial offsets of variable components from the host objects, and light curves. Detection completeness was examined by simulating light curves for periodic and irregular variability. We detected optical variability for 36 ± 2% (51 ± 3% for a bright sample with i′ \u3c 24.4 mag) of X-ray sources in the field. Number densities of variable obejcts as functions of time intervals t and variable component magnitudes i′ vari are obtained. Number densities of variable stars, SNe, and AGN are 120, 489, and 579 objects deg−2, respectively. Bimodal distributions of variable stars in the color-magnitude diagrams indicate that the variable star sample consists of bright (V 22 mag) blue variable stars of the halo population and faint (V 23.5 mag) red variable stars of the disk population. There are a few candidates of RR Lyrae providing a possible number density of 10−2 kpc−3 at a distance of \u3e 150 kpc from the Galactic center