474 research outputs found
Performances of Herschel/PACS bolometer arrays and future developments at CEA
The European Space Agency is building a space telescope to observe the Universe in the Far-IR and sub-millimeter regime of the electromagnetic spectrum. The scientific payload is composed of three instruments. One of them, PACS, is equipped with a novel type of bolometer arrays developed by CEA in the late 90's. We briefly present the PACS Photometer and the architecture of CEA filled bolometer arrays. We accessed the physics of the detectors and thoroughly measured their performances by developing a pragmatic calibration procedure. The Photometer is now calibrated and integrated on the focal plane of the observatory. The launch is scheduled for April 2009. Meanwhile, CEA is working on adapting PACS bolometers to longer wavelength for wide-field ground-based telescopes, and for the future cold-telescope space mission SPICA
CEA Bolometer Arrays: the First Year in Space
The CEA/LETI and CEA/SAp started the development of far-infrared filled bolometer arrays for space applications
over a decade ago. The unique design of these detectors makes possible the assembling of large focal planes
comprising thousands of bolometers running at 300 mK with very low power dissipation. Ten arrays of 16x16
pixels were thoroughly tested on the ground, and integrated in the Herschel/PACS instrument before launch in
May 2009. These detectors have been successfully commissioned and are now operating in their nominal environment
at the second Lagrangian point of the Earth-Sun system. In this paper we briefly explain the functioning
of CEA bolometer arrays, and we present the properties of the detectors focusing on their noise characteristics,
the effect of cosmic rays on the signal, the repeatability of the measurements, and the stability of the system
A Catalog of MIPSGAL Disk and Ring Sources
We present a catalog of 416 extended, resolved, disk- and ring-like objects
as detected in the MIPSGAL 24 micron survey of the Galactic plane. This catalog
is the result of a search in the MIPSGAL image data for generally circularly
symmetric, extended "bubbles" without prior knowledge or expectation of their
physical nature. Most of the objects have no extended counterpart at 8 or 70
micron, with less than 20% detections at each wavelength. For the 54 objects
with central point sources, the sources are nearly always seen in all IRAC
bands. About 70 objects (16%) have been previously identified, with another 35
listed as IRAS sources. Among the identified objects, those with central
sources are mostly listed as emission-line stars, but with other source types
including supernova remnants, luminous blue variables, and planetary nebulae.
The 57 identified objects (of 362) without central sources are nearly all PNe
(~90%).which suggests that a large fraction of the 300+ unidentified objects in
this category are also PNe. These identifications suggest that this is
primarily a catalog of evolved stars. Also included in the catalog are two
filamentary objects that are almost certainly SNRs, and ten unusual compact
extended objects discovered in the search. Two of these show remarkable spiral
structure at both 8 and 24 micron. These are likely background galaxies
previously hidden by the intervening Galactic plane
Image synthesis with a convolutional capsule generative adversarial network
Machine learning for biomedical imaging often suffers from a lack of labelled training data. One solution is to use generative models to synthesise more data. To this end, we introduce CapsPix2Pix, which combines convolutional capsules with the pix2pix framework, to synthesise images conditioned on class segmentation labels. We apply our approach to a new biomedical dataset of cortical axons imaged by two-photon microscopy, as a method of data augmentation for small datasets. We evaluate performance both qualitatively and quantitatively. Quantitative evaluation is performed by using image data generated by either CapsPix2Pix or pix2pix to train a U-net on a segmentation task, then testing on real microscopy data. Our method quantitatively performs as well as pix2pix, with an order of magnitude fewer parameters. Additionally, CapsPix2Pix is far more capable at synthesising images of different appearance, but the same underlying geometry. Finally, qualitative analysis of the features learned by CapsPix2Pix suggests that individual capsules capture diverse and often semantically meaningful groups of features, covering structures such as synapses, axons and noise
The stable climate of KELT-9b
Even among the most irradiated gas giants, so-called ultra-hot Jupiters, KELT-9b stands out as the hottest planet thus far discovered with a dayside temperature of over 4500 K. At these extreme irradiation levels, we expect an increase in heat redistribution efficiency and a low Bond albedo owed to an extended atmosphere with molecular hydrogen dissociation occurring on the planetary dayside. We present new photometric observations of the KELT-9 system throughout 4 full orbits and 9 separate occultations obtained by the 30 cm space telescope CHEOPS. The CHEOPS bandpass, located at optical wavelengths, captures the peak of the thermal emission spectrum of KELT-9b. In this work we simultaneously analyse CHEOPS phase curves along with public phase curves from TESS and Spitzer to infer joint constraints on the phase curve variation, gravity-darkened transits, and occultation depth in three bandpasses, as well as derive 2D temperature maps of the atmosphere at three different depths. We find a day-night heat redistribution efficiency of ~0.3 which confirms expectations of enhanced energy transfer to the planetary nightside due to dissociation and recombination of molecular hydrogen. We also calculate a Bond albedo consistent with zero. We find no evidence of variability of the brightness temperature of the planet, excluding variability greater than 1
Deep reinforcement learning for subpixel neural tracking
Automatically tracing elongated structures, such as axons and blood vessels, is a challenging problem in the field of biomedical imaging, but one with many downstream applications. Real, labelled data is sparse, and existing algorithms either lack robustness to different datasets, or otherwise require significant manual tuning. Here, we instead learn a tracking algorithm in a synthetic environment, and apply it to tracing axons. To do so, we formulate tracking as a reinforcement learning problem, and apply deep reinforcement learning techniques with a continuous action space to learn how to track at the subpixel level. We train our model on simple synthetic data and test it on mouse cortical two-photon microscopy images. Despite the domain gap, our model approaches the performance of a heavily engineered tracker from a standard analysis suite for neuronal microscopy. We show that fine-tuning on real data improves performance, allowing better transfer when real labelled data is available. Finally, we demonstrate that our model's uncertainty measure-a feature lacking in hand-engineered trackers-corresponds with how well it tracks the structure
The Great Observatories All-Sky LIRG Survey: Herschel Image Atlas and Aperture Photometry
Far-infrared (FIR) images and photometry are presented for 201 Luminous and
Ultraluminous Infrared Galaxies [LIRGs: log, ULIRGs: log], in the Great
Observatories All-Sky LIRG Survey (GOALS) based on observations with the
Photodetector Array Camera and Spectrometer
(PACS) and the Spectral and Photometric Imaging Receiver (SPIRE) instruments.
The image atlas displays each GOALS target in the three PACS bands (70, 100,
and 160 m) and the three SPIRE bands (250, 350, and 500 m), optimized
to reveal structures at both high and low surface brightness levels, with
images scaled to simplify comparison of structures in the same physical areas
of kpc. Flux densities of companion galaxies in
merging systems are provided where possible, depending on their angular
separation and the spatial resolution in each passband, along with integrated
system fluxes (sum of components). This dataset constitutes the imaging and
photometric component of the GOALS Herschel OT1 observing program, and is
complementary to atlases presented for the Hubble Space Telescope (Evans et al.
2017, in prep.), Spitzer Space Telescope (Mazzarella et al. 2017, in prep.),
and Chandra X-ray Observatory (Iwasawa et al. 2011, 2017, in prep.).
Collectively these data will enable a wide range of detailed studies of AGN and
starburst activity within the most luminous infrared galaxies in the local
Universe.Comment: Accepted for publication in ApJS, 270 pages, 216 figures, 4 table
Infrared photometric study of the massive star forming region S235 using Spitzer-IRAC and JHK observations
We present the {\it Spitzer}-IRAC images of the S235 star forming complex
that includes the East~1 & 2, Central and S235 A & B regions. In addition, we
present the near-infrared images of the S235 A & B regions. The IRAC photometry
reveals on-going star formation, with 86 Class 0/I and 144 Class II YSOs in the
entire S235 complex. Nearly 73% of these YSOs are present in clusters with a
maximum surface density of 120 YSOs/pc (in the vicinity of S235A & B
regions). A few YSOs, possibly in an arc-like formation, are identified towards
the south of S235A region, which may be speculated as an evidence for
magnetically super-critical collapse. One of the sources in the arc-like
formation, namely S235AB-MIR, seems to be a young, massive star that is still
accreting matter. SED modeling of some of the newly identified YSOs confirms
the classification made on the basis of IRAC colours. The IRAC ratio map of
Ch2/Ch4 traces clearly the Br emission associated with the HII region
of S235A within the horse-shoe envelope. Outside the horse-shoe structure, the
ratio map indicates shock-excited H emission. Br emission is also
seen around S235B (from the ratio map). The ratio map of Ch2/Ch4 reveals that
the source "e2s3" in the East~2 region may be associated with shock-excited
H emission outflow or jet. The SED modeling of this new source indicates
that it is a very young massive star that is not yet able to drive an HII
region.Comment: 19 pages; 13 figures; 8 tables. Accepted in MNRAS, Feb 201
The NIKA instrument: results and perspectives towards a permanent KID based camera for the Pico Veleta observatory
The New IRAM KIDs Array (NIKA) is a pathfinder instrument devoted to
millimetric astronomy. In 2009 it was the first multiplexed KID camera on the
sky; currently it is installed at the focal plane of the IRAM 30-meters
telescope at Pico Veleta (Spain). We present preliminary data from the last
observational run and the ongoing developments devoted to the next NIKA-2
kilopixels camera, to be commissioned in 2015. We also report on the latest
laboratory measurements, and recent improvements in detector cosmetics and
read-out electronics. Furthermore, we describe a new acquisition strategy
allowing us to improve the photometric accuracy, and the related automatic
tuning procedure.Comment: 24th International Symposium on Space Terahertz Technology, ISSTT
2013, April 8 to 10, 2013, Groningen, the Netherland
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