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- techniques: imaging spectroscopy (5)
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Institut
Most image restoration methods in astronomy rely upon probabilistic tools that infer the best solution for a deconvolution problem. They achieve good performances when the point spread function (PSF) is spatially invariant in the image plane.
However, this condition is not always satisfied in real optical systems. We propose a new method for the restoration of images affected by static and anisotropic aberrations using Deep Neural Networks that can be directly applied to sky images.
The network is trained using simulated sky images corresponding to the T80-S Telescope optical model, a 80-cm survey imager at Cerro Tololo (Chile), which are synthesized using a Zernike polynomial representation of the optical system.
Once trained, the network can be used directly on sky images, outputting a corrected version of the image that has a constant and known PSF across its field of view. The method is to be tested on the T80-S Telescope.
We present the method and results on synthetic data.
Convolutional neural networks (CNNs) have been used for a wide range of applications in astronomy, including for the restoration of degraded images using a spatially invariant point spread function (PSF) across the field of view. Most existing development techniques use a single PSF in the deconvolution process, which is unrealistic when spatially variable PSFs are present in real observation conditions. Such conditions are simulated in this work to yield more realistic data samples. We propose a method that uses a simulated spatially variable PSF for the T80-South (T80-S) telescope, an 80-cm survey imager at Cerro Tololo (Chile). The synthetic data use real parameters from the detector noise and atmospheric seeing to recreate the T80-S observational conditions for the CNN training. The method is tested on real astronomical data from the T80-S telescope. We present the simulation and training methods, the results from real T80-S image CNN prediction, and a comparison with space observatory Gaia. A CNN can fix optical aberrations, which include image distortion, PSF size and profile, and the field position variation while preserving the source's flux. The proposed restoration approach can be applied to other optical systems and to post-process adaptive optics static residual aberrations in large-diameter telescopes.
A long-standing and profound problem in astronomy is the difficulty in obtaining deep near-infrared observations due to the extreme brightness and variability of the night sky at these wavelengths. A solution to this problem is crucial if we are to obtain the deepest possible observations of the early Universe, as redshifted starlight from distant galaxies appears at these wavelengths. The atmospheric emission between 1,000 and 1,800 nm arises almost entirely from a forest of extremely bright, very narrow hydroxyl emission lines that varies on timescales of minutes. The astronomical community has long envisaged the prospect of selectively removing these lines, while retaining high throughput between them. Here we demonstrate such a filter for the first time, presenting results from the first on-sky tests. Its use on current 8 m telescopes and future 30 m telescopes will open up many new research avenues in the years to come.
Dispersion engineered silicon nitride waveguides by geometrical and refractive-index optimization
(2014)
Dispersion engineering in silicon nitride (SiXNY) waveguides is investigated through the optimization of the waveguide transversal dimensions and refractive indices in a multicladding arrangement. Ultraflat dispersion of -84.0 +/- 0.5 ps/nm/km between 1700 and 2440 nm and 1.5 +/- 3 ps/nm/km between 1670 and 2500 nm is numerically demonstrated. It is shown that typical refractive index fluctuations as well as dimension fluctuations during fabrication of the SiXNY waveguides are a limitation for obtaining ultraflat dispersion profiles. Single- and multicladding waveguides are fabricated and their dispersion profiles measured (over nearly 1000 nm) using a low-coherence frequency domain interferometric technique. By appropriate thickness optimization, the zero-dispersion wavelength is tuned over a large spectral range in single-and multicladding waveguides with small refractive index contrast (3%). A flat dispersion profile with +/- 3.2 ps/nm/km variation over 500 nm is obtained in a multicladding waveguide fabricated with a refractive index contrast of 37%. Finally, we generate a nearly three-octave supercontinuum in this dispersion flattened multicladding SiXNY waveguide. (C) 2014 Optical Society of America
sent observations of the Type Ia supernova SN 2002er during the brightening phase. The observations were performed with the Potsdam Multi Aperture Spectrophotometer (PMAS) integral field instrument. Due to the 8arcsecx8 arcsec field of view of the spectrograph an accurate background subtraction was possible. Results from analyses of the evolution of absorption features in comparisons with other SNe show that SN 2002er is a fairly bright Type Ia supernova with a peak brightness of MB=-19.6+/-0.1.
We report preliminary results from a targeted investigation on quasars containing damped Lyman-alpha absorption (DLA) lines as well strong metal absorption lines, carried out with the Potsdam Multi Aperture Spectrophotometer (PMAS). We search for line-emitting objects at the same redshift as the absorption lines and close to the line of sight of the QSOs. We have observed and detected the already confirmed absorbing galaxies in Q2233+131 (Z(abs) = 3.15) and Q0151+045 (Z(abs),= 0.168), while failing to find spectral signatures for the z = 0.091 absorber in Q0738+313. From the Q2233+131 DLA galaxy, we have detected extended Lyalpha emission from an area of 3" x 5"
This paper presents observations of an extended Lyman-alpha emission nebula surrounding the galaxy responsible for the Damped Lyman-alpha Absorption (DLA) line in the spectrum of the quasar Q2233+131. With the Potsdam Multi Aperture Spectrophotometer (PMAS) we measure the properties of the extended Lyalpha emission in an area of 3" x 5" having a total line flux of (2.8 +/- 0.3) x 10(-16) erg cm(-2) s(-1), which at redshift z = 3.15 corresponds to a luminosity of (2.4(-0.2)(+0.3)) x 10(43) erg s(-1) and a size of 23 x 38 kpc. The location of the emission is spatially coincident with the previously detected DLA galaxy, but extends significantly beyond its limb. We argue that the Lya emission is likely to be caused by an outflow from the DLA galaxy, presumably powered by star formation. In the case of negligible dust extinction, the Lya luminosity indicates a star-formation rate of 19 +/- 10 M-. yr(-1) consistent with that derived from the UV continuum flux from the parent galaxy. The wind velocity indicated by the integral field spectra is of the order of several hundred km s(-1). We find no indication of emission originating in a rotating disk
The spectrum of the quasar PHL 1226 is known to have a strong Mg II and sub-damped Lymanalpha (sub-DLA) absorption line system with N(H I) = (5 +/- 2) x 10(19) cm(-2) at z = 0.1602. Using integral field spectra from the Potsdam Multi Aperture Spectrophotometer (PMAS) we investigate a galaxy at an impact parameter of 6".4 which is most probably responsible for the absorption lines. A fainter galaxy at a similar redshift and a slightly larger distance from the QSO is known to exist, but we assume that the absorption is caused by the more nearby galaxy. From optical Balmer lines we estimate an intrinsic reddening consistent with 0, and a moderate star formation rate of 0.5 M-circle dot yr(-1) is inferred from the Ha luminosity. Using nebular emission line ratios we find a solar oxygen abundance 12 + log (O/H) = 8.7 +/- 0.1 and a solar nitrogen to oxygen abundance ratio log (N/O) = -1.0 +/- 0.2. This abundance is larger than those of all known sub-DLA systems derived from analyses of metal absorption lines in quasar spectra. On the other hand, the properties are compatible with the most metal rich galaxies responsible for strong Mg II absorption systems. These two categories can be reconciled if we assume an abundance gradient similar to local galaxies. Under that assumption we predict abundances 12 + log (O/H) = 7.1 and log (N/O) = -1.9 for the sub-DLA cloud, which is similar to high redshift DLA and sub-DLA systems. We find evidence for a rotational velocity of similar to200 km s(-1) over a length of similar to7 kpc. From the geometry and kinematics of the galaxy we estimate that the absorbing cloud does not belong to a rotating disk, but could originate in a rotating halo
We utilise multi-epoch MUSE spectroscopy to study binary stars in the core of the Galactic globular cluster NGC 3201. Our sample consists of 3553 stars with 54 883 spectra in total comprising 3200 main-sequence stars up to 4 magnitudes below the turn-off. Each star in our sample has between 3 and 63 (with a median of 14) reliable radial velocity measurements within five years of observations. We introduce a statistical method to determine the probability of a star showing radial velocity variations based on the whole inhomogeneous radial velocity sample. Using HST photometry and an advanced dynamical MOCCA simulation of this specific cluster we overcome observational biases that previous spectroscopic studies had to deal with. This allows us to infer a binary frequency in the MUSE field of view and enables us to deduce the underlying true binary frequency of (6.75 +/- 0.72)% in NGC 3201. The comparison of the MUSE observations with the MOCCA simulation suggests a large portion of primordial binaries. We can also confirm a radial increase in the binary fraction towards the cluster centre due to mass segregation. We discovered that in the core of NGC 3201 at least (57.5 +/- 7.9)% of blue straggler stars are in a binary system. For the first time in a study of globular clusters, we were able to fit Keplerian orbits to a significant sample of 95 binaries. We present the binary system properties of eleven blue straggler stars and the connection to SX Phoenicis-type stars. We show evidence that two blue straggler formation scenarios, the mass transfer in binary (or triple) star systems and the coalescence due to binary-binary interactions, are present in our data. We also describe the binary and spectroscopic properties of four sub-subgiant (or red straggler) stars. Furthermore, we discovered two new black hole candidates with minimum masses (M sin i) of (7.68 +/- 0.50)M-circle dot, (4.4 +/- 2.8)M-circle dot, and refine the minimum mass estimate on the already published black hole to (4.53 +/- 0.21)M-circle dot, These black holes are consistent with an extensive black hole subsystem hosted by NGC 3201.
A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources
(2019)
Aims. Globular clusters produce many exotic stars due to a much higher frequency of dynamical interactions in their dense stellar environments. Some of these objects were observed together with several hundred thousand other stars in our MUSE survey of 26 Galactic globular clusters. Assuming that at least a few exotic stars have exotic spectra (i.e. spectra that contain emission lines), we can use this large spectroscopic data set of over a million stellar spectra as a blind survey to detect stellar exotica in globular clusters. Methods. To detect emission lines in each spectrum, we modelled the expected shape of an emission line as a Gaussian curve. This template was used for matched filtering on the di fferences between each observed 1D spectrum and its fitted spectral model. The spectra with the most significant detections of H alpha emission are checked visually and cross-matched with published catalogues. Results. We find 156 stars with H alpha emission, including several known cataclysmic variables (CV) and two new CVs, pulsating variable stars, eclipsing binary stars, the optical counterpart of a known black hole, several probable sub-subgiants and red stragglers, and 21 background emission-line galaxies. We find possible optical counterparts to 39 X-ray sources, as we detected H alpha emission in several spectra of stars that are close to known positions of Chandra X-ray sources. This spectral catalogue can be used to supplement existing or future X-ray or radio observations with spectra of potential optical counterparts to classify the sources.