Abstract
This paper presents the third data release of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP), a wide-field multi-band imaging survey with the Subaru 8.2 m telescope. HSC-SSP has ...three survey layers (Wide, Deep, and UltraDeep) with different area coverages and depths, designed to address a wide array of astrophysical questions. This third release from HSC-SSP includes data from 278 nights of observing time and covers about 670 deg2 in all five broad-band filters (grizy) at the full depth (∼26 mag at 5σ depending on filter) in the Wide layer. If we include partially observed areas, the release covers 1470 deg2. The Deep and UltraDeep layers have $\sim\! 80\%$ of the originally planned integration times, and are considered done, as we have slightly changed the observing strategy in order to compensate for various time losses. There are a number of updates in the image processing pipeline. Of particular importance is the change in the sky subtraction algorithm; we subtract the sky on small scales before the detection and measurement stages, which has significantly reduced the number of false detections. Thanks to this and other updates, the overall quality of the processed data has improved since the previous release. However, there are limitations in the data (for example, the pipeline is not optimized for crowded fields), and we encourage the user to check the quality assurance plots as well as a list of known issues before exploiting the data. The data release website is 〈https://hsc-release.mtk.nao.ac.jp〉.
Abstract
The Hyper Suprime-Cam (HSC) is an 870 megapixel prime focus optical imaging camera for the 8.2 m Subaru telescope. The wide-field corrector delivers sharp images of 0${^{\prime\prime}_{.}}$2 ...(FWHM) in the HSC-i band over the entire 1${^{\circ}_{.}}$5 diameter field of view. The collimation of the camera with respect to the optical axis of the primary mirror is done with hexapod actuators, the mechanical accuracy of which is a few microns. Analysis of the remaining wavefront error in off-focus stellar images reveals that the collimation of the optical components meets design specifications. While there is a flexure of mechanical components, it also is within the design specification. As a result, the camera achieves its seeing-limited imaging on Maunakea during most of the time; the median seeing over several years of observing is 0${^{\prime\prime}_{.}}$67 (FWHM) in the i band. The sensors use p-channel, fully depleted CCDs of 200 μm thickness (2048 × 4176 15 μm square pixels) and we employ 116 of them to pave the 50 cm diameter focal plane. The minimum interval between exposures is 34 s, including the time to read out arrays, to transfer data to the control computer, and to save them to the hard drive. HSC on Subaru uniquely features a combination of a large aperture, a wide field of view, sharp images and a high sensitivity especially at longer wavelengths, which makes the HSC one of the most powerful observing facilities in the world.
Abstract
Recent detection of gravitational waves from a neutron star (NS) merger event GW170817 and identification of an electromagnetic counterpart provide a unique opportunity to study the physical ...processes in NS mergers. To derive properties of ejected material from the NS merger, we perform radiative transfer simulations of kilonova, optical and near-infrared emissions powered by radioactive decays of r-process nuclei synthesized in the merger. We find that the observed near-infrared emission lasting for >10 d is explained by 0.03 M⊙ of ejecta containing lanthanide elements. However, the blue optical component observed at the initial phases requires an ejecta component with a relatively high electron fraction (Ye). We show that both optical and near-infrared emissions are simultaneously reproduced by the ejecta with a medium Ye of ∼0.25. We suggest that a dominant component powering the emission is post-merger ejecta, which exhibits that the mass ejection after the first dynamical ejection is quite efficient. Our results indicate that NS mergers synthesize a wide range of r-process elements and strengthen the hypothesis that NS mergers are the origin of r-process elements in the Universe.
Abstract
We have developed an automated quick data analysis system for data quality assurance (QA) for Hyper Suprime-Cam (HSC). The system was commissioned in 2012–2014, and has been offered for ...general observations, including the HSC Subaru Strategic Program, since 2014 March. The system provides observers with data quality information, such as seeing, sky background level, and sky transparency, based on quick analysis as data are acquired. Quick-look images and validation of image focus are also provided through an interactive web application. The system is responsible for the automatic extraction of QA information from acquired raw data into a database, to assist with observation planning, assess progress of all observing programs, and monitor long-term efficiency variations of the instrument and telescope. Enhancements of the system are being planned to facilitate final data analysis, to improve the HSC archive, and to provide legacy products for astronomical communities.
Abstract
GW170817 is the first detected gravitational wave source from a neutron star merger. We present the Japanese collaboration for gravitational-wave electro-magnetic (J-GEM) follow-up ...observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5 mag decline in the z band during the period between 1.7 and 7.7 d after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder during later epochs: the z − H color has changed by approximately 2.5 mag during the period between 0.7 and 7.7 d. The rapid evolutions of both the color and the optical brightness are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized r-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that r-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with an ejecta mass of 0.01 M⊙, which suggests a more intense mass ejection (∼0.03 M⊙) or possibly an additional energy source.
Subaru Prime Focus Camera — Suprime-Cam Miyazaki, Satoshi; Komiyama, Yutaka; Sekiguchi, Maki ...
Publications of the Astronomical Society of Japan,
12/2002, Letnik:
54, Številka:
6
Journal Article
Recenzirano
Odprti dostop
We have built an 80-mega pixels (
$10240 \times 8192$
) mosaic CCD camera, called Suprime-Cam, for the wide-field prime focus of the 8.2 m Subaru telescope. Suprime-Cam covers a field of view
$34' ...\times 27'$
, a unique facility among the 8–10 m class telescopes, with a resolution of
${0\rlap {.}{}^{\mathrm {\prime \prime }}202}$
per pixel. The focal plane consists of ten high-resistivity
$2\mathrm{k} \times 4\mathrm{k}$
CCDs developed by MIT Lincoln Laboratory, which are cooled by a large Stirling-cycle cooler. The CCD readout electronics was designed to be scalable, which allows the multiple read-out of tens of CCDs. It takes 50 seconds to readout entire arrays. We designed a filter-exchange mechanism of the jukebox type that can hold up to ten large filters (
$205\times 170 \times 15 \,\mathrm{mm}^3$
). The wide-field corrector is basically a three-lens Wynne-type, but has a new type of atmospheric dispersion corrector. The corrector provides a flat focal plane and an un-vignetted field of view of
$30'$
in diameter. The achieved co-planarity of the focal array mosaic is smaller than 30
$\,{\mu \mathrm {m}}$
peak-to-peak, which realizes mostly the seeing limited image over the entire field. The median seeing in the
$I_\mathrm{c}$
-band, measured over one year and a half, is
${0\rlap {.}{}^{\mathrm {\prime \prime }}61}$
. The PSF anisotropy in Suprime-Cam images, estimated by stellar ellipticities, is about 2% under this median seeing condition. At the time of commissioning, Suprime-Cam had the largest survey speed, which is defined as the field of view multiplied by the primary mirror area of the telescope, among those cameras built for sub-arcsecond imaging.
We present the photometric properties of a sample of infrared (IR) bright dust-obscured galaxies (DOGs). Combining wide and deep optical images obtained with the Hyper Suprime-Cam on the Subaru ...Telescope and all-sky mid-IR (MIR) images taken with Wide-Field Infrared Survey Explorer, we discovered 48 DOGs with i − K
s > 1.2 and i − 22 > 7.0, where i, K
s, and 22 represent AB magnitude in the i-band, K
s-band, and 22 μm, respectively, in the GAMA 14 hr field (∼ 9 deg2). Among these objects, 31 (∼ 65%) show power-law spectral energy distributions (SEDs) in the near-IR (NIR) and MIR regime, while the remainder show an NIR bump in their SEDs. Assuming that the redshift distribution for our DOGs sample is Gaussian, with mean and sigma z = 1.99 ± 0.45, we calculated their total IR luminosity using an empirical relation between 22 μm luminosity and total IR luminosity. The average value of the total IR luminosity is (3.5 ± 1.1) × 1013 L⊙, which classifies them as hyper-luminous infrared galaxies. We also derived the total IR luminosity function (LF) and IR luminosity density (LD) for a flux-limited subsample of 18 DOGs with 22 μm flux greater than 3.0 mJy and with i-band magnitude brighter than 24 AB magnitude. The derived space density for this subsample is log ϕ = −6.59 ± 0.11 Mpc−3. The IR LF for DOGs including data obtained from the literature is fitted well by a double-power law. The derived lower limit for the IR LD for our sample is ρIR ∼ 3.8 × 107 L⊙ Mpc−3 and its contributions to the total IR LD, IR LD of all ultra-luminous infrared galaxies, and that of all DOGs are > 3%, > 9%, and > 15%, respectively.
Kiso Supernova Survey (KISS): Survey strategy Morokuma, Tomoki; Tominaga, Nozomu; Tanaka, Masaomi ...
Publications of the Astronomical Society of Japan,
12/2014, Letnik:
66, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Abstract
The Kiso Supernova Survey (KISS) is a high-cadence optical wide-field supernova (SN) survey. The primary goal of the survey is to catch the very early light of a SN, during the shock ...breakout phase. Detection of SN shock breakouts combined with multi-band photometry obtained with other facilities would provide detailed physical information on the progenitor stars of SNe. The survey is performed using a 2 $_{.}^{\circ}$2 × 2 $_{.}^{\circ}$2 field-of-view instrument on the 1.05-m Kiso Schmidt telescope, the Kiso Wide Field Camera (KWFC). We take a 3-min exposure in g-band once every hour in our survey, reaching magnitude g ∼ 20–21. About 100 nights of telescope time per year have been spent on the survey since 2012 April. The number of the shock breakout detections is estimated to be of the order of 1 during our three-year project. This paper summarizes the KISS project including the KWFC observing setup, the survey strategy, the data reduction system, and CBET-reported SNe discovered so far by KISS.
Cluster star-forming galaxies are found to have an excess of far-infrared emission relative to Hα, when compared to those in the field, which could be caused by intense active galactic nuclei (AGN) ...activity, dust and/or declining star formation histories. Here we present spectroscopic observations of Hα emitters in the Cl 0939+4713 (Abell 851) super-cluster at z = 0.41, using AF2+ WYFFOS on the William Herschel Telescope. We measure O ii, Hβ, O iii, Hα and N ii for a sample of 119 Hα emitters in and around the cluster. We find that 17 ± 5 per cent of the Hα emitters are AGN, irrespective of environment. For star-forming galaxies, we obtain Balmer decrements, metallicities and ionization parameters with different methods, individually and by stacking. We find a strong mass–metallicity relation at all environments, with no significant dependence on environment. The ionization parameter declines with increasing stellar mass for low-mass galaxies. Hα emitters residing in intermediate environments show the highest ionization parameters (along with high O iii/Hα and high O iii/O ii line ratios, typically twice as large as in the highest and lowest densities), which decline with increasing environmental density. Dust extinction (AHα) correlates strongly with stellar mass, but also with environmental density. Star-forming galaxies in the densest environments are found to be significantly dustier (AHα ≈ 1.5 − 1.6) than those residing in the lowest density environments (AHα ≈ 0.6), deviating significantly from what would be predicted given their stellar masses.
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