A wide field survey at the Northern Ecliptic Pole

Compact refractive adaptive optics (CRAO) is a visible compact adaptive optics (AO) system optimized for small telescopes. It was mounted on the 1.3 m Araki telescope of Koyama Astronomical Observatory (KAO) in Kyoto Sangyo University, Japan. CRAO aims to improve the natural seeing 3” to 0.8” at 500 nm at the KAO site. Thus, it needs a large format and highly frequent camera for wide field survey (WFS) and a largely segmented depth map (DM) because the natural seeing ∼3” at the KAO site is especially poor for astronomical observations. To improve the performance of CRAO with a new WFS and DM, we searched for the optimal AO parameters (the number of WFS subapertures (N_WFS), the number of DM actuators (N_DM), and the loop frequency (<i>f</i>_L) with two AO simulators using <i>yao</i> and <i>COMPASS</i>. Consequently, we found that N_WFS &gt; 12×12, N_DM &gt; 80, and <i>f</i>_L &gt; 800 Hz are necessary to achieve the full width at half maximum (FWHM) &lt; 0.8” for point spread function (PSF) under the KAO site’s atmospheric conditions. Finally, we calculated the limiting magnitude (V_lim) with commercially available sensors for WFS and DMs. By combining ORCA-Lightning (Hamamatsu Photonics) and DM97-15 (ALPAO), a deeper limiting magnitude (V_lim ∼ 4.4) can be achieved, even with a 1 m-class telescope.

We report the results of optical–infrared follow-up observations of the gravitational wave (GW) event GW151226 detected by the Advanced LIGO in the framework of J-GEM (Japanese collaboration for Gravitational wave ElectroMagnetic follow-up). We performed wide-field optical imaging surveys with the Kiso Wide Field Camera (KWFC), Hyper Suprime-Cam (HSC), and MOA-cam3. The KWFC survey started at 2.26 d after the GW event and covered 778 deg2 centered at the high Galactic region of the skymap of GW151226. We started the HSC follow-up observations from ∼12 d after the event and covered an area of 63.5 deg2 of the highest probability region of the northern sky with limiting magnitudes of 24.6 and 23.8 for the i and z bands, respectively. MOA-cam3 covered 145 deg2 of the skymap with the MOA-red filter ∼2.5 mon after the GW alert. The total area covered by the wide-field surveys was 986.5 deg2. The integrated detection probability for the observed area was ∼29%. We also performed galaxy-targeted observations with six optical and near-infrared telescopes from 1.61 d after the event. A total of 238 nearby (≤100 Mpc) galaxies were observed with a typical I band limiting magnitude of ∼19.5. We detected 13 supernova candidates with the KWFC survey, and 60 extragalactic transients with the HSC survey. Two thirds of the HSC transients were likely supernovae and the remaining one third were possible active galactic nuclei. With our observational campaign, we found no transients that are likely to be associated with GW151226.

We report on a search for the optical counterparts of 175 um - selected sources from the Far-Infrared Background (FIRBACK) survey in the European Large Area ISO Survey (ELAIS) N2 field. Applying a likelihood ratio technique to optical catalogues from the Isaac Newton Telescope - Wide Field Survey (INT--WFS), we found optical identifications for 33 out of 55 FIRBACK sources in this field. These were then reassessed in the light of associations with the ELAIS final catalogue for the the N2 field, to yield a final set of 31 associations. We have investigated the nature of this population through a comparison of their observed spectral energy distributions with predictions from radiative transfer models which simulate the emission from both cirrus and starburst components. We find the far-infrared sources to be 80 per cent star bursting galaxies with their starburst component at a high optical depth. The resulting SEDs were used to estimate far-infrared luminosities, star formation rates, dust temperatures and dust masses. The N2 FIRBACK population is found to consist of four suspected ULIRGs, a number of LIRGs and a population of low redshift quiescently star forming galaxies. We also discuss the implications of these results for current evolutionary models.

Weak gravitational lensing measurements from the large-scale structure of the Universe probe the growth of structures at different epochs, thereby providing information about the mysterious dark energy component. Wide-field redshift surveys such as WFIRST, Euclid and LSST will image the sky and collect an unprecedented amount of data. The decrease in the statistical errors must necessarily be accompanied by an increase in our understanding of systematic errors. The sources of the systematic errors could be i) astrophysical, such as intrinsic alignments, failure to account for the complex morphology of the galaxies when estimating lensing distortions, or could be ii) foreground effects such as the Point Spread Function (PSF) or imperfections from the detectors etc. The systematic errors are estimated by testing the shear estimation pipeline on mock galaxy images that are forward-simulated from first principles. The simulated galaxy images must have realistic properties for the estimates of the systematic biases to be accurate. In this thesis, I describe in detail the work done towards incorporating in the image simulations some of the detector effects relevant for WFIRST and understanding the limitations of using images from narrow surveys, such as COSMOS, as input into image simulations for wide field surveys.

All focussing x-ray telescopes that have been in orbit (Einstein, EXOSAT, and ROSAT) or are currently being developed (e.g., ASTRO-D, SAX, AXAF, and XMM) are based upon the same type of optics, the Wolter Type I system or a conical approximation of it. With funding, weight, and volume now being severely limited, new investigations in x-ray astronomy will have to specialize on a particular study, e.g., wide field surveys, spectroscopy, broad band measurements, and should have significantly more capability than the current missions in that study. Several novel approaches to broad band and wide field optics have been described in the literature that may be able to satisfy certain specific objectives better than the Wolter I.

Strong gravitationally lensed supernovae (SNe) are a powerful probe for cosmology and stellar physics. The relative time delays between lensed SN images provide an independent way of measuring a fundamental cosmological parameter – the Hubble constant –, the value of which is currently under debate. The time delays also serve as a “time machine”, offering a unique opportunity to capture the extremely early phase of the SN explosion, which can be used to constrain the SN progenitor and explosion mechanism. Although there are only a handful of strongly lensed SN discoveries so far, which greatly hinders scientific applications, the sample size is expected to grow substantially with next-generation surveys. In this work, we investigate the capability of detecting strongly lensed SNe with the China Space Station Telescope (CSST), a two-meter space telescope to be launched around 2026. Through Monte Carlo simulations, we predict that CSST can detect 1008.53 and 51.78 strongly lensed SNe from its Wide Field Survey (WFS, covering 17 500 deg2) and Deep Field Survey (DFS, covering 400 deg2) over the course of ten years. In both surveys, about 35% of the events involve Type Ia SNe as the background sources. Our results suggest that the WFS and DFS of CSST, although not designed or optimized for discovering transients, can still make a great contribution to the strongly lensed SNe studies.

INT WFS pipeline processing

The Cosmic Evolution Survey (COSMOS) is a Hubble Space Telescope (HST) treasury project.The COSMOS aims to perform a 2 square degree imaging survey of an equatorial field in $I$(F814W) band, using the Advanced Camera for Surveys (ACS). Such a wide field survey, combined with ground-based photometric and spectroscopic data, is essential to understand the interplay between large scale structure, evolution and formation of galaxies and dark matter. In 2004, we have obtained high-quality, broad band images of the COSMOS field ($B, V, r^\prime, i^\prime,$ and $ z^\prime$) using Suprime-Cam on the Subaru Telescope, and we have started our new optical multi-band program, COSMOS-21 in 2005. Here, we present a brief summary of the current status of the COSMOS project together with contributions from the Subaru Telescope. Our future Subaru program, COSMOS-21, is also discussed briefly.

Astrophysics and cosmology in the coming decades urgently need a large field-of-view (FOV), highly multiplexed spectroscopic survey telescope satisfying challenging image quality and stability requirements. The 6.5 m MUltiplexed Survey Telescope (MUST) proposed by Tsinghua University will be constructed on the Saishiteng Mountain of Northwest China to improve the spectroscopic survey capability of ground-based optical telescopes. In this paper, we demonstrate the conceptual design of the optical system of MUST. MUST will adopt a 6.5 m primary mirror, a 2.45 m secondary mirror, and a multiple-element widefield corrector (WFC) to ensure excellent image quality with an 80% encircled energy size of image spots less than ~ 0.6 arcsec in diameter for the entire 3° FOV and the whole 50° zenith angle range. Thanks to its compact 6.5 m Ritchey-Chretien system and 20,000 optical fibers on its Cassegrain focus, MUST will carry out state-of-the-art wide-field spectroscopic surveys with efficiency ~ 19 times higher than the Dark Energy Spectroscopic Instrument (DESI) using a measure proposed by Ellis et al. Upon completion around 2029, MUST will be one of the world's most advanced wide-field spectroscopic survey telescopes and a new essential reference for the future development of wide-field survey telescopes. It will enable significant advances in many fields in astrophysics and cosmology.

Chinese astronomical community has suggested to construct a high resolution precision and wide field survey of universal optical / infrared telescope, suitable for a wide range of cutting-edge scientific research subject. The telescope diameter is 12 meters, and it is composed of 84 pieces of hexagonal mirrors. After the completion, it could be a world's largest telescope. Its wide field survey function will be work together with the 30 meters telescope in the near future on the observation of complementary. The telescope optical system adopted innovative design ideas, its multiple focuses can achieve rapid switching; its atmospheric dispersion corrector lens-prism can correct aberration also, and with the advantage of simple structure; two layers of Nasmyth platform can be placed more scientific instruments. LAMOST, a Chinese large spectrum survey telescope has been built and put into operation many years, it has successfully developed the two segmented optical mirrors and one of them is with deformation of thin mirror active optical technology, as well as the batch grinding hexagonal off-axis mirror technology developed in recent years, for construction of the 12 meters telescope laid a good technical foundation.

The cosmological nature of gamma-ray bursts (GRBs) implies that a small portion of them could be gravitationally lensed by foreground objects during their propagation. The gravitational lensing effect on the GRB prompt emission and on-axis afterglows has been discussed, and some candidates have been found in the literature. In this work, considering the high detection rate of GRB orphan afterglows in future wide-field survey era, we investigate the gravitationally lensed orphan afterglows in view of three lens models, i.e. the point-mass model, the singular isothermal sphere model, and the Chang–Refsdal model. The structure of the GRB jet itself is also incorporated in calculating the lensed afterglow light curves. It is found that lensed optical/X-ray orphan afterglows in principle could be diagnosed through their temporal characteristics, and the optical band is the best band to observe the galaxy-lensed orphan afterglows. Moreover, the event rate for galaxy-lensed orphan afterglows is estimated to be ≲ 1.8 yr−1 for the whole sky. If most orphan afterglows could be identified (from other transients in the survey data), the optimistic detection rates of the 2.5 m Wide Field Survey Telescope of China and 8.4 m Vera Rubin Observatory Legacy Survey of Space and Time for galaxy-lensed orphan afterglows in the optical band are ≲ 0.01–0.02 and ≲ 0.04–0.08 yr−1, respectively.

The properties of galaxy clusters in the local universe have been fairly well determined in the past few decades, and wide field surveys in the near infrared are converging on a statistically significant sample of high redshift clusters. These catalogs may soon allow discrimination between the competing models of galaxy formation and evolution [1]. The Oxford‐Dartmouth Thirty Degree Survey (ODT) will span four widely separated 3° × 3° fields, to B < 26 in UBVRi’Z with an extension in the near‐infrared to K < 19. With more than half of the survey completed, this deep, wide‐area, multi‐color dataset has yielded a large sample of K‐selected clusters to probe the formation and evolution history of galaxies in dense environments. An exploration of cluster color‐magnitude slopes and intercepts [2], luminosity functions [3], and morphological distributions [4, 5] should constrain the relative dominance of star formation rates and merger events on cluster galaxy evolution. Here, we present our cluster‐finding method and preliminary results.

Type Iax supernovae may arise from failed explosions of white dwarfs (WDs) that leave behind a bound remnant (i.e., a “postgenitor” star) that could be identified in wide field surveys. To understand their observational signatures, we simulate these WD postgenitors from shortly after explosion until they move back down the WD cooling track, and we consider several possible WD masses and explosion energies. To predict the peculiar surface abundances of the WD postgenitors, our models take into account gravitational settling and radiative levitation. We find that radiative levitation is significant at temperatures above a mass-dependent critical temperature, typically in the range T eff ≈ (50–100) × 103 K, significantly increasing surface abundances of iron group elements. Due to enhanced iron group opacity compared to normal WDs, the postgenitor peak luminosity and cooling timescale depend sensitively on mass, with more massive WDs becoming brighter but cooling much faster. We discuss our results in light of recently discovered hypervelocity WDs with peculiar surface compositions, finding that our low-mass postgenitor models match many of their observational characteristics. Finally, we explore the effects of thermohaline diffusion, tentatively finding that it strongly suppresses abundance enhancements created by radiative levitation, but more realistic modeling is required to reach a firm conclusion.

I review the status of science with wide field surveys. For many decades surveys have been the backbone of astronomy, and the main engine of discovery, as we have mapped the sky at every possible wavelength. Surveys are an efficient use of resources. They are important as a fundamental resource; to map intrinsically large structures; to gain the necessary statistics to address some problems; and to find very rare objects. I summarise major recent wide field surveys - 2MASS, SDSS, 2dfGRS, and UKIDSS - and look at examples of the exciting science they have produced, covering the structure of the Milky Way, the measurement of cosmological parameters, the creation of a new field studying substellar objects, and the ionisation history of the Universe. I then look briefly at upcoming projects in the optical-IR survey arena - VISTA, PanSTARRS, WISE, and LSST. Finally I ask, now we have opened up essentially all wavelength windows, whether the exploration of survey discovery space is ended. I examine other possible axes of discovery space, and find them mostly to be too expensive to explore or otherwise unfruitful, with two exceptions : the first is the time axis, which we have only just begun to explore properly; and the second is the possibility of neutrino astrophysics.

Application of CMOS image sensors with non-destructive readout capability have several advantages over current CCD sensors in detecting Near-Earth Objects (NEOs). They include detection of temporal changes, cosmic ray rejection, no charge blooming, expanded dynamic range, and lower dark current. Since wide field survey usually requires large mosaics, a “rolling shutter” operation simplifies the challenge of large mechanical shutters. Being able to readout parts of the field in destructive mode offers the possibility of providing guiding feedback to the telescope during exposure. We have carried out preliminary testing of a prototype CMOS camera built by Spectral Instruments Inc. on a one-meter telescope on Mt. Lemmon, Arizona as applied to rapidly moving NEOs. We have also demonstrated “post facto” guiding on a known NEO that significantly improves the signal to noise.