scholarly journals Search Methods for Globular Cluster Candidates in M31

2002 ◽  
Vol 207 ◽  
pp. 146-148
Author(s):  
Juan C. Seguel ◽  
Doug Geisler ◽  
Myung Gyoon Lee ◽  
Sang Chul Kim ◽  
Ata Sarajedini ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Point Spread Function ◽  
Globular Clusters ◽  
Visual Inspection ◽  
Wide Field ◽  
Search Methods ◽  
Cluster Systems ◽  
Point Spread ◽  
Spread Function ◽  
Nearby Galaxies

Searching for globular cluster candidates in nearby galaxies such as M31 is the first step to study the characteristics of extragalactic globular cluster systems. Previous searches for M31 globular clusters were mostly based on visual inspection of photograpic plates. We have selected globular cluster candidates from a wide-field Washington CCD survey of M31, using various methods: color-magnitude diagrams, color-color diagrams, point spread function subtraction and visual inspection of the objects. The efficiency and accuracy of these methods for finding globular clusters are presented.

scholarly journals Surface Brightness Profiles of 68 Globular Clusters Derived From Electronic Camera Recordings

1980 ◽  
Vol 85 ◽  
pp. 459-460
Author(s):  
Gerald E. Kron ◽  
Katherine C. Gordon ◽  
Anthony V. Hewitt
Keyword(s):  
Point Spread Function ◽  
Globular Clusters ◽  
Surface Brightness ◽  
Naval Observatory ◽  
Point Spread ◽  
Spread Function ◽  
Spacial Information ◽  
Cluster Profiles ◽  
Star Images ◽  
The U.S

Images of 68 globular clusters have been recorded in 125 exposures made with the electronic camera of the U.S. Naval Observatory on the 24-inch, 40-inch and 61-inch reflecting telescopes at the Flagstaff Station. The images were electronically malfocussed to allow the integration of light from the fainter cluster stars without saturation of the central portions of the brighter star images. Spacial information thus lost was partly regained by subsequent linear deconvolution of the cluster profiles by means of a star profile used as the point spread function.

Improving position accuracy for telescopes with small aperture and wide field of view utilizing point spread function modelling

2020 ◽  
Vol 497 (3) ◽  
pp. 4000-4008
Author(s):  
Rongyu Sun ◽  
Shengxian Yu ◽  
Peng Jia ◽  
Changyin Zhao
Keyword(s):  
Point Spread Function ◽  
Large Scale ◽  
Field Of View ◽  
Wide Field ◽  
Position Measurement ◽  
Small Aperture ◽  
Position Accuracy ◽  
Point Spread ◽  
Wide Field Of View ◽  
Spread Function

ABSTRACT Telescopes with a small aperture and a wide field of view are widely used and play a significant role in large-scale state-of-the-art sky survey applications, such as transient detection and near-Earth object observations. However, owing to the specific defects caused by optical aberrations, the image quality and efficiency of source detection are affected. To achieve high-accuracy position measurements, an innovative technique is proposed. First, a large number of raw images are analysed using principal component analysis. Then, the effective point spread function is reconstructed, which reflects the state of the telescope and reveals the characteristics of the imaging process. Finally, based on the point spread function model, the centroids of star images are estimated iteratively. To test the efficiency and reliability of our algorithm, a large number of simulated images are produced, and a telescope with small aperture and wide field of view is utilized to acquire the raw images. The position measurement of sources is performed using our novel method and two other common methods on these data. Based on a comparison of the results, the improvement is investigated, and it is demonstrated that our proposed technique outperforms the others on position accuracy. We explore the limitations and potential gains that may be achieved by applying this technique to custom systems designed specifically for wide-field astronomical applications.

scholarly journals Direct imaging of haloes and truncations in face-on nearby galaxies

2015 ◽  
Vol 11 (S317) ◽  
pp. 39-44
Author(s):  
J. H. Knapen ◽  
S. P. C. Peters ◽  
P. C. van der Kruit ◽  
I. Trujillo ◽  
J. Fliri ◽  
...  
Keyword(s):  
Point Spread Function ◽  
Spiral Galaxies ◽  
Surface Photometry ◽  
Direct Imaging ◽  
Point Spread ◽  
Deep Imaging ◽  
Spread Function ◽  
Stellar Halo ◽  
Nearby Galaxies ◽  
Proper Analysis

AbstractWe use ultra-deep imaging from the IAC Stripe 82 Legacy Project to study the surface photometry of 22 nearby, face-on to moderately inclined spiral galaxies. The reprocessed and co-added SDSS/Stripe 82 imaging allows us to probe down to 29–30 r′-mag/arcsec2 and thus reach into the very faint outskirts of the galaxies. We find extended stellar haloes in over half of our sample galaxies, and truncations in three of them. The presence of stellar haloes and truncations is mutually exclusive, and we argue that the presence of a stellar halo can hide a truncation. We find that the onset of the halo and the truncation scales tightly with galaxy size. We highlight the importance of a proper analysis of the extended wings of the point spread function (PSF), finding that around half the light at the faintest levels is from the inner regions of a galaxy, though not the nucleus, re-distributed to the outskirts by the PSF. We discuss implications of this effect for future deep imaging surveys, such as with the LSST.

Point spread function degradation model of a polarization imaging system for wide-field subwavelength nanoparticles

2020 ◽  
Vol 59 (23) ◽  
pp. 7114 ◽  
Author(s):  
Wu Qiong ◽  
Kun Gan ◽  
Zizheng Hua ◽  
Zhenzhou Zhang ◽  
Hanwen Zhao ◽  
...  
Keyword(s):  
Point Spread Function ◽  
Imaging System ◽  
Wide Field ◽  
Degradation Model ◽  
Polarization Imaging ◽  
Point Spread ◽  
Spread Function

scholarly journals Point spread function modelling for wide-field small-aperture telescopes with a denoising autoencoder

2020 ◽  
Vol 493 (1) ◽  
pp. 651-660 ◽  
Author(s):  
Peng Jia ◽  
Xiyu Li ◽  
Zhengyang Li ◽  
Weinan Wang ◽  
Dongmei Cai
Keyword(s):  
Point Spread Function ◽  
Wide Field ◽  
Calibration Data ◽  
Post Processing ◽  
Denoising Autoencoder ◽  
Small Aperture ◽  
Point Spread ◽  
Spread Function ◽  
Function Modelling ◽  
Star Images

ABSTRACT The point spread function reflects the state of an optical telescope and it is important for the design of data post-processing methods. For wide-field small-aperture telescopes, the point spread function is hard to model because it is affected by many different effects and has strong temporal and spatial variations. In this paper, we propose the use of a denoising autoencoder, a type of deep neural network, to model the point spread function of wide-field small-aperture telescopes. The denoising autoencoder is a point spread function modelling method, based on pure data, which uses calibration data from real observations or numerical simulated results as point spread function templates. According to real observation conditions, different levels of random noise or aberrations are added to point spread function templates, making them realizations of the point spread function (i.e. simulated star images). Then we train the denoising autoencoder with realizations and templates of the point spread function. After training, the denoising autoencoder learns the manifold space of the point spread function and it can map any star images obtained by wide-field small-aperture telescopes directly to its point spread function. This could be used to design data post-processing or optical system alignment methods.

scholarly journals The Point Spread Function Variations inside Wide-field Astonomical Images

10.14311/1696 ◽  
2013 ◽  
Vol 53 (1) ◽  
Author(s):  
Elena Anisimova ◽  
Jan Bednář ◽  
Petr Páta
Keyword(s):  
Point Spread Function ◽  
Imaging System ◽  
Wide Field ◽  
Optical Aberrations ◽  
Atmospheric Scattering ◽  
Function Fitting ◽  
Astronomical Imaging ◽  
Point Spread ◽  
Spread Function ◽  
Field Imaging

The Point Spread Function (PSF) of the astronomical imaging system is usually approximated by a Gaussian or Moffat function. For simplification, the astronomical imaging system is considered to be time and space invariant. This means that invariable PSF within an exposed image is assumed. If real wide-field imaging systems are considered, this presumption is not fulfilled. In real systems, stronger optical aberrations are expected (especially coma) at greater distances from the center of the captured image. This impacts the efficiency of stellar astrometry and photometry algorithms, so it is necessary to know the PSF variation. In this paper, we perform the first step toward assigning PSF changes: we study the dependence of the Moffat function fitting parameters (FWHM and the atmospheric scattering coefficient ) on the position of a stellar object.

scholarly journals HST Color-Magnitude Diagrams of Globular Clusters in NGC 185 and NGC 205

1999 ◽  
Vol 192 ◽  
pp. 231-236 ◽  
Author(s):  
Doug Geisler ◽  
Taft Armandroff ◽  
Gary Da Costa ◽  
Myung Gyoon Lee ◽  
Ata Sarajedini
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
High Spatial Resolution ◽  
Minor Component ◽  
Cluster Systems ◽  
Accurate Knowledge ◽  
Complete Knowledge ◽  
Nearby Galaxies ◽  
The Individual ◽  
Composite Properties

We present a progress report on our ongoing HST WFPC2 study of globular clusters in NGC 185 and NGC 205. Most of the cluster candidates studied previously only from the ground are indeed globular clusters; however, several candidates turn out to be either foreground stars or background galaxies. In addition, we have discovered one new, previously unsuspected cluster. A complete knowledge of the globular cluster systems in even these nearby galaxies requires high spatial resolution data. We then derive preliminary I, (V – I) color-magnitude diagrams for some of the clusters, as well as for their surrounding fields. The clusters show the blue horizontal branches expected for the low metallicities we derive, which are in agreement with those derived from ground-based integrated spectra. The fields appear generally more metal-rich than indicated by previous ground-based studies. The field blue horizontal branch in NGC 185 is only a very minor component, while that in NGC 205 is even smaller. After all of our observations have been acquired, these data will allow a very accurate knowledge of the individual and composite properties of the globular cluster systems of these 2 galaxies, as well as those of their field stars.

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