scholarly journals Successful application of PSF-R techniques to the case of the globular cluster NGC 6121 (M 4)

2020 ◽  
Vol 634 ◽  
pp. L5 ◽  
Author(s):  
D. Massari ◽  
A. Marasco ◽  
O. Beltramo-Martin ◽  
J. Milli ◽  
G. Fiorentino ◽  
...  

Context. Precise photometric and astrometric measurements on astronomical images require an accurate knowledge of the point spread function (PSF). When the PSF cannot be modelled directly from the image, PSF-reconstruction techniques become the only viable solution. So far, however, their performance on real observations has rarely been quantified. Aims. In this Letter, we test the performance of a novel hybrid technique, called PRIME, on Adaptive Optics-assisted SPHERE/ZIMPOL observations of the Galactic globular cluster NGC 6121. Methods. PRIME couples PSF-reconstruction techniques, based on control-loop data and direct image fitting performed on the only bright point-like source available in the field of view of the ZIMPOL exposures, with the aim of building the PSF model. Results. By exploiting this model, the magnitudes and positions of the stars in the field can be measured with an unprecedented precision, which surpasses that obtained by more standard methods by at least a factor of four for on-axis stars and by up to a factor of two on fainter, off-axis stars. Conclusions. Our results demonstrate the power of PRIME in recovering precise magnitudes and positions when the information directly coming from astronomical images is limited to only a few point-like sources and, thus, paving the way for a proper analysis of future Extremely Large Telescope observations of sparse stellar fields or individual extragalactic objects.

2003 ◽  
Vol 19 (5) ◽  
Author(s):  
Pablo Artal ◽  
Li Chen ◽  
Enrique J Fernández ◽  
Ben Singer ◽  
Silvestre Manzanera ◽  
...  

2004 ◽  
Vol 202 ◽  
pp. 99-102
Author(s):  
B. R. Oppenheimer ◽  
R. G. Dekany ◽  
M. Troy ◽  
T. Hayward ◽  
B. Brandl

We present a study of the Palomar Adaptive Optics System and the PHARO near infrared camera in coronagraphic mode. The camera provides two different focal plane occulting masks–opaque circular disks 0.43 and 0.97″ across. Three different pupil plane apodizing masks (Lyot masks) are also provided. The six different combinations of Lyot mask and focal plane mask suppress differently the point spread function of a bright star centered on the focal plane mask. We obtained images of the bright nearby star Gliese 614 with all six different configurations in the K filter. We measured the dynamic range achievable with these configurations. Within 2.5″, the dynamic range is at least 8 magnitudes at the 5σ level and as high as 12 in a 1 s exposure. This represents a substantial gain over similar techniques without adaptive optics.


2020 ◽  
Vol 638 ◽  
pp. A98
Author(s):  
F. Cantalloube ◽  
O. J. D. Farley ◽  
J. Milli ◽  
N. Bharmal ◽  
W. Brandner ◽  
...  

Context. The wind-driven halo is a feature that is observed in images that were delivered by the latest generation of ground-based instruments that are equipped with an extreme adaptive optics system and a coronagraphic device, such as SPHERE at the Very Large Telescope (VLT). This signature appears when the atmospheric turbulence conditions vary faster than the adaptive optics loop can correct for. The wind-driven halo is observed as a radial extension of the point spread function along a distinct direction (this is sometimes referred to as the butterfly pattern). When this is present, it significantly limits the contrast capabilities of the instrument and prevents the extraction of signals at close separation or extended signals such as circumstellar disks. This limitation is consequential because it contaminates the data for a substantial fraction of the time: about 30% of the data produced by the VLT/SPHERE instrument are affected by the wind-driven halo. Aims. This paper reviews the causes of the wind-driven halo and presents a method for analyzing its contribution directly from the scientific images. Its effect on the raw contrast and on the final contrast after post-processing is demonstrated. Methods. We used simulations and on-sky SPHERE data to verify that the parameters extracted with our method can describe the wind-driven halo in the images. We studied the temporal, spatial, and spectral variation of these parameters to point out its deleterious effect on the final contrast. Results. The data-driven analysis we propose provides information to accurately describe the wind-driven halo contribution in the images. This analysis confirms that this is a fundamental limitation of the finally reached contrast performance. Conclusions. With the established procedure, we will analyze a large sample of data delivered by SPHERE in order to propose post-processing techniques that are tailored to removing the wind-driven halo.


2006 ◽  
Vol 457 (1) ◽  
pp. 359-363 ◽  
Author(s):  
E. Gendron ◽  
Y. Clénet ◽  
T. Fusco ◽  
G. Rousset

1998 ◽  
Vol 37 (21) ◽  
pp. 4614 ◽  
Author(s):  
Jean-Marc Conan ◽  
Laurent M. Mugnier ◽  
Thierry Fusco ◽  
Vincent Michau ◽  
Gérard Rousset

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