Pub Date : 2019-11-13DOI: 10.1142/s2251171719800035
S. Wagner
{"title":"Book Review: \"Cherenkov Reflections: Gamma-Ray Imaging and the Evolution of TeV Astronomy by David Fegan\"","authors":"S. Wagner","doi":"10.1142/s2251171719800035","DOIUrl":"https://doi.org/10.1142/s2251171719800035","url":null,"abstract":"","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":"1 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"63849037","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-11-13DOI: 10.1142/S2251171719500156
C. Mackay
Astronomers working with faint targets will benefit greatly from improved image quality on current and planned ground-based telescopes. At present, most adaptive optic systems are targeted at the highest resolution with bright guide stars. We demonstrate a significantly new approach for measuring low-order wavefront errors by using a pupil-plane curvature wavefront sensor design. By making low order wavefront corrections, we can deliver significant improvements in image resolution in the visible on telescopes in the 2.5–8.2 m range on good astronomical sites. As a minimum, the angular resolution will be improved by a factor of 2.5–3 under any reasonable conditions and, with further correction and image selection, even sharper images may be obtained routinely. We re-examine many of the assumptions about what may be achieved with faint reference stars to achieve this performance. We show how our new design of curvature wavefront sensor combined with wavefront fitting routines based on radon transforms allow this performance to be achieved routinely. Simulations over a wide range of conditions match the performance already achieved in runs with earlier versions of the hardware described. Reference stars significantly fainter than I [Formula: see text]17[Formula: see text]m may be used routinely to produce images with a near diffraction limited core and halo much smaller than that delivered by natural seeing.
{"title":"High-Resolution Imaging in the Visible with Faint Reference Stars on Large Ground-Based Telescopes","authors":"C. Mackay","doi":"10.1142/S2251171719500156","DOIUrl":"https://doi.org/10.1142/S2251171719500156","url":null,"abstract":"Astronomers working with faint targets will benefit greatly from improved image quality on current and planned ground-based telescopes. At present, most adaptive optic systems are targeted at the highest resolution with bright guide stars. We demonstrate a significantly new approach for measuring low-order wavefront errors by using a pupil-plane curvature wavefront sensor design. By making low order wavefront corrections, we can deliver significant improvements in image resolution in the visible on telescopes in the 2.5–8.2 m range on good astronomical sites. As a minimum, the angular resolution will be improved by a factor of 2.5–3 under any reasonable conditions and, with further correction and image selection, even sharper images may be obtained routinely. We re-examine many of the assumptions about what may be achieved with faint reference stars to achieve this performance. We show how our new design of curvature wavefront sensor combined with wavefront fitting routines based on radon transforms allow this performance to be achieved routinely. Simulations over a wide range of conditions match the performance already achieved in runs with earlier versions of the hardware described. Reference stars significantly fainter than I [Formula: see text]17[Formula: see text]m may be used routinely to produce images with a near diffraction limited core and halo much smaller than that delivered by natural seeing.","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":" ","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1142/S2251171719500156","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42861811","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-10-16DOI: 10.1142/s2251171719500144
T. Kuiper, M. Franco, S. Smith, G. Baines, L. Greenhill, S. Horiuchi, T. Olin, D. Price, D. Shaff, L. Teitelbaum, S. Weinreb, L. White, I. Zaw
A dual beam, dual polarization, low noise receiver has been installed at a Cassegrain focus of the NASA 70[Formula: see text]m antenna near Canberra, Australia. It operates in five pairs of 1[Formula: see text]GHz bands from 17 to 27[Formula: see text]GHz simultaneously. The receiver temperature measured at the feed is 21–22[Formula: see text]K at 22[Formula: see text]GHz and, during dry winter night-time conditions, zenith system temperatures as low as 35[Formula: see text]K have been observed in the 21–22[Formula: see text]GHz band. The native polarization is linear but can be converted to circular prior to down-conversion. The downconverters have complex mixers, followed by quadrature hybrids which can be bypassed or used to convert the quadrature phase channels into an upper and lower sideband, each 1000[Formula: see text]MHz wide. For spectroscopy, four ROACH1 signal processors each currently providing 32[Formula: see text]K channel spectra across four 1000[Formula: see text]MHz bands, for 0.4[Formula: see text]km/s velocity resolution at 22[Formula: see text]GHz. Using both beam- and position-switching, the receiver achieved a noise level of 5[Formula: see text]mK r.m.s. in an hour of integration and 31[Formula: see text]kHz resolution. The NASA 70[Formula: see text]m antennas have a 45 arcsec beamwidth at 22[Formula: see text]GHz and an aperture efficiency of 35.5% giving a sensitivity of 0.49[Formula: see text]K/Jy.
{"title":"The 17–27 GHz Dual Horn Receiver on the NASA 70 m Canberra Antenna","authors":"T. Kuiper, M. Franco, S. Smith, G. Baines, L. Greenhill, S. Horiuchi, T. Olin, D. Price, D. Shaff, L. Teitelbaum, S. Weinreb, L. White, I. Zaw","doi":"10.1142/s2251171719500144","DOIUrl":"https://doi.org/10.1142/s2251171719500144","url":null,"abstract":"A dual beam, dual polarization, low noise receiver has been installed at a Cassegrain focus of the NASA 70[Formula: see text]m antenna near Canberra, Australia. It operates in five pairs of 1[Formula: see text]GHz bands from 17 to 27[Formula: see text]GHz simultaneously. The receiver temperature measured at the feed is 21–22[Formula: see text]K at 22[Formula: see text]GHz and, during dry winter night-time conditions, zenith system temperatures as low as 35[Formula: see text]K have been observed in the 21–22[Formula: see text]GHz band. The native polarization is linear but can be converted to circular prior to down-conversion. The downconverters have complex mixers, followed by quadrature hybrids which can be bypassed or used to convert the quadrature phase channels into an upper and lower sideband, each 1000[Formula: see text]MHz wide. For spectroscopy, four ROACH1 signal processors each currently providing 32[Formula: see text]K channel spectra across four 1000[Formula: see text]MHz bands, for 0.4[Formula: see text]km/s velocity resolution at 22[Formula: see text]GHz. Using both beam- and position-switching, the receiver achieved a noise level of 5[Formula: see text]mK r.m.s. in an hour of integration and 31[Formula: see text]kHz resolution. The NASA 70[Formula: see text]m antennas have a 45 arcsec beamwidth at 22[Formula: see text]GHz and an aperture efficiency of 35.5% giving a sensitivity of 0.49[Formula: see text]K/Jy.","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":" ","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45671390","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-10DOI: 10.1142/S2251171719500107
A. Rasha, T. Natusch, C. Granet, S. Gulyaev
A number of countries have identified redundant large telecommunications antennas (TA) and indicated their intention to convert them into radio telescopes (RT). As the efficiency of a parabolic dish radio telescope depends on its surface quality and optical alignment, a careful assessment of these properties should be undertaken before conversion. Here, as a case study, we describe a laser scanning (LS) procedure we developed and used for the Warkworth 30[Formula: see text]m Cassegrain antenna. To investigate gravity-induced mechanical deformation of the antenna surfaces and structure, we conducted measurements at elevation angles ranging from 6 to 90 degrees. The ability of a laser scanner to survey its nominal [Formula: see text] steradian surroundings allows for simultaneous study of the main and subreflectors, readily permitting a dynamic investigation of variation of the telescope optics as elevation changes occur. In particular, the method we present here allows determination of the surface quality of both main and subreflectors, the displacement between centers of the reflectors, their relative rotations and focal length variation as a function of elevation angle. We discuss details of settings, measurements, data processing and analysis focusing on possible difficulties and pitfalls. In our case study, no significant elevation-dependent surface deformation of the reflectors was observed, with the overall standard deviation of the postfit residuals varying between 1.0 and 1.7[Formula: see text]mm as elevation angle changes from 90∘ to 6∘, respectively. We, therefore, conclude that in our case both the main reflector and the subreflector, as well as the telescope optics, remain unaffected by gravitational deformation within the accuracy of the measurements, a conclusion that can possibly be extended to the similar class of TA currently considered for conversion.
{"title":"Conversion of a Telecommunications Antenna into a Radio Telescope: Laser Scanner Measurements of Optics and Dish Surface Quality of a Cassegrain Antenna","authors":"A. Rasha, T. Natusch, C. Granet, S. Gulyaev","doi":"10.1142/S2251171719500107","DOIUrl":"https://doi.org/10.1142/S2251171719500107","url":null,"abstract":"A number of countries have identified redundant large telecommunications antennas (TA) and indicated their intention to convert them into radio telescopes (RT). As the efficiency of a parabolic dish radio telescope depends on its surface quality and optical alignment, a careful assessment of these properties should be undertaken before conversion. Here, as a case study, we describe a laser scanning (LS) procedure we developed and used for the Warkworth 30[Formula: see text]m Cassegrain antenna. To investigate gravity-induced mechanical deformation of the antenna surfaces and structure, we conducted measurements at elevation angles ranging from 6 to 90 degrees. The ability of a laser scanner to survey its nominal [Formula: see text] steradian surroundings allows for simultaneous study of the main and subreflectors, readily permitting a dynamic investigation of variation of the telescope optics as elevation changes occur. In particular, the method we present here allows determination of the surface quality of both main and subreflectors, the displacement between centers of the reflectors, their relative rotations and focal length variation as a function of elevation angle. We discuss details of settings, measurements, data processing and analysis focusing on possible difficulties and pitfalls. In our case study, no significant elevation-dependent surface deformation of the reflectors was observed, with the overall standard deviation of the postfit residuals varying between 1.0 and 1.7[Formula: see text]mm as elevation angle changes from 90∘ to 6∘, respectively. We, therefore, conclude that in our case both the main reflector and the subreflector, as well as the telescope optics, remain unaffected by gravitational deformation within the accuracy of the measurements, a conclusion that can possibly be extended to the similar class of TA currently considered for conversion.","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":" ","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1142/S2251171719500107","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46502001","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-10DOI: 10.1142/S2251171719500090
J. Tutt, R. McEntaffer, D. Miles, B. Donovan, Christopher R. Hillman
High-resolution, high-throughput soft X-ray spectroscopy using reflection gratings has the potential to unlock answers to many of the questions about the high-energy Universe. To enable missions to use this technology in the future, the ability to precisely align reflection gratings needs to be demonstrated. The Water Recovery X-ray Rocket (WRXR), a soft X-ray spectrometer that successfully launched in April 2018 from the Kwajalein Atoll, required co-aligned X-ray reflection gratings. WRXR was designed to produce a moderate-resolution spectrum of the Vela supernova remnant over a large field-of-view. The grating module was manufactured, integrated onto the rocket payload, passed environmental testing and was successfully launched and recovered. This paper describes the grating and mirror alignment methodologies for WRXR, and their inherent systematic uncertainties. Improvements to the alignment method that are required to meet the tighter alignment tolerances of future X-ray spectrometers are also discussed.
{"title":"Grating Alignment for the Water Recovery X-Ray Rocket (WRXR)","authors":"J. Tutt, R. McEntaffer, D. Miles, B. Donovan, Christopher R. Hillman","doi":"10.1142/S2251171719500090","DOIUrl":"https://doi.org/10.1142/S2251171719500090","url":null,"abstract":"High-resolution, high-throughput soft X-ray spectroscopy using reflection gratings has the potential to unlock answers to many of the questions about the high-energy Universe. To enable missions to use this technology in the future, the ability to precisely align reflection gratings needs to be demonstrated. The Water Recovery X-ray Rocket (WRXR), a soft X-ray spectrometer that successfully launched in April 2018 from the Kwajalein Atoll, required co-aligned X-ray reflection gratings. WRXR was designed to produce a moderate-resolution spectrum of the Vela supernova remnant over a large field-of-view. The grating module was manufactured, integrated onto the rocket payload, passed environmental testing and was successfully launched and recovered. This paper describes the grating and mirror alignment methodologies for WRXR, and their inherent systematic uncertainties. Improvements to the alignment method that are required to meet the tighter alignment tolerances of future X-ray spectrometers are also discussed.","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":" ","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1142/S2251171719500090","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48774802","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-01DOI: 10.1142/S2251171719500077
Brent Belland, J. Gunn, D. Reiley, J. Cohen, E. Kirby, Antonio Cesar de Oliveira, L. Oliveira, Mitsuko K. Roberts, M. Seiffert
Focal ratio degradation (FRD), the decrease of light’s focal ratio between the input into an optical fiber and the output, is important to characterize for astronomical spectrographs due to its effects on throughput and the point spread function. However, while FRD is a function of many fiber properties such as stresses, microbending, and surface imperfections, angular misalignments between the incoming light and the face of the fiber also affect the light profile and complicate this measurement. A compact experimental setup and a model separating FRD from angular misalignment was applied to a fiber subjected to varying stresses or angular misalignments to determine the magnitude of these effects. The FRD was then determined for a fiber in a fiber positioner that will be used in the Subaru Prime Focus Spectrograph (PFS). The analysis we carried out for the PFS positioner suggests that effects of angular misalignment dominate and no significant FRD increase due to stress should occur.
{"title":"Focal Ratio Degradation for Fiber Positioner Operation in Astronomical Spectrographs","authors":"Brent Belland, J. Gunn, D. Reiley, J. Cohen, E. Kirby, Antonio Cesar de Oliveira, L. Oliveira, Mitsuko K. Roberts, M. Seiffert","doi":"10.1142/S2251171719500077","DOIUrl":"https://doi.org/10.1142/S2251171719500077","url":null,"abstract":"Focal ratio degradation (FRD), the decrease of light’s focal ratio between the input into an optical fiber and the output, is important to characterize for astronomical spectrographs due to its effects on throughput and the point spread function. However, while FRD is a function of many fiber properties such as stresses, microbending, and surface imperfections, angular misalignments between the incoming light and the face of the fiber also affect the light profile and complicate this measurement. A compact experimental setup and a model separating FRD from angular misalignment was applied to a fiber subjected to varying stresses or angular misalignments to determine the magnitude of these effects. The FRD was then determined for a fiber in a fiber positioner that will be used in the Subaru Prime Focus Spectrograph (PFS). The analysis we carried out for the PFS positioner suggests that effects of angular misalignment dominate and no significant FRD increase due to stress should occur.","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":" ","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1142/S2251171719500077","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42640630","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-24DOI: 10.1142/S2251171719500120
J. Armstrong, A. Jorgensen, D. Mozurkewich, H. Neilson, E. Baines, H. Schmitt, G. V. van Belle
We introduce an observational tool based on visibility nulls in optical spectro-interferometry fringe data to probe the structure of stellar atmospheres. In a preliminary demonstration, we use both Navy Precision Optical Interferometer (NPOI) data and stellar atmosphere models to show that this tool can be used, for example, to investigate limb darkening. Using bootstrapping with either multiple linked baselines or multiple wavelengths in optical and infrared spectro-interferometric observations of stars makes it possible to measure the spatial frequency [Formula: see text] at which the real part of the fringe visibility [Formula: see text] vanishes. That spatial frequency is determined by [Formula: see text], where [Formula: see text] is the projected baseline length, and [Formula: see text] is the wavelength at which the null is observed. Since [Formula: see text] changes with the Earth’s rotation, [Formula: see text] also changes. If [Formula: see text] is constant with wavelength, [Formula: see text] varies in direct proportion to [Formula: see text]. Any departure from that proportionality indicates that the brightness distribution across the stellar disk varies with wavelength via variations in limb darkening, in the angular size of the disk, or both. In this paper, we introduce the use of variations of [Formula: see text] with [Formula: see text] as a means of probing the structure of stellar atmospheres. Using the equivalent uniform disk diameter [Formula: see text], given by [Formula: see text], as a convenient and intuitive parameterization of [Formula: see text], we demonstrate this concept by using model atmospheres to calculate the brightness distribution for [Formula: see text] Ophiuchi and to predict [Formula: see text], and then comparing the predictions to coherently averaged data from observations taken with the NPOI.
{"title":"Interferometric Fringe Visibility Null as a Function of Spatial Frequency: A Probe of Stellar Atmospheres","authors":"J. Armstrong, A. Jorgensen, D. Mozurkewich, H. Neilson, E. Baines, H. Schmitt, G. V. van Belle","doi":"10.1142/S2251171719500120","DOIUrl":"https://doi.org/10.1142/S2251171719500120","url":null,"abstract":"We introduce an observational tool based on visibility nulls in optical spectro-interferometry fringe data to probe the structure of stellar atmospheres. In a preliminary demonstration, we use both Navy Precision Optical Interferometer (NPOI) data and stellar atmosphere models to show that this tool can be used, for example, to investigate limb darkening. Using bootstrapping with either multiple linked baselines or multiple wavelengths in optical and infrared spectro-interferometric observations of stars makes it possible to measure the spatial frequency [Formula: see text] at which the real part of the fringe visibility [Formula: see text] vanishes. That spatial frequency is determined by [Formula: see text], where [Formula: see text] is the projected baseline length, and [Formula: see text] is the wavelength at which the null is observed. Since [Formula: see text] changes with the Earth’s rotation, [Formula: see text] also changes. If [Formula: see text] is constant with wavelength, [Formula: see text] varies in direct proportion to [Formula: see text]. Any departure from that proportionality indicates that the brightness distribution across the stellar disk varies with wavelength via variations in limb darkening, in the angular size of the disk, or both. In this paper, we introduce the use of variations of [Formula: see text] with [Formula: see text] as a means of probing the structure of stellar atmospheres. Using the equivalent uniform disk diameter [Formula: see text], given by [Formula: see text], as a convenient and intuitive parameterization of [Formula: see text], we demonstrate this concept by using model atmospheres to calculate the brightness distribution for [Formula: see text] Ophiuchi and to predict [Formula: see text], and then comparing the predictions to coherently averaged data from observations taken with the NPOI.","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":" ","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42949889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-06-06DOI: 10.1142/s2251171719800011
P. Coles
{"title":"Book Review: \"Data Analysis for Scientists and Engineers by Edward L. Robinson (Princeton University Press, 2016)\"","authors":"P. Coles","doi":"10.1142/s2251171719800011","DOIUrl":"https://doi.org/10.1142/s2251171719800011","url":null,"abstract":"","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":" ","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1142/s2251171719800011","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43872490","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-06-04DOI: 10.1142/s2251171719500132
A. Guyonnet, S. Dagoret-Campagne, N. Mondrik
Ground-based astronomy has to correct astronomical observations from the impact of the atmospheric transparency and its variability. The current objective of several observatories is to achieve a sub-percent-level monitoring of atmospheric transmission. A promising approach has been to combine internal calibration of the observations with various external meteorological data sources, upon availability and depending on quality. In this paper we investigate the use of the NASA Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) which is a general circulation model (GCM) and data assimilation system that renders freely available for any given site, at any time, all the parameters constraining atmospheric transmission. This paper demonstrates the extraction of the relevant atmospheric parameters for optical astronomy at two sites: Mauna Kea in Hawaii and Cerro Tololo International Observatory in Chile. The temporal variability for the past eight years (annual, overnight, and hourly) as well as the spatial gradients of ozone, precipitable water vapor, and aerosol optical depth are presented and their respective impacts on the atmospheric transparency are analyzed.
{"title":"Local Monitoring of Atmospheric Transparency from the NASA MERRA-2 Global Assimilation System","authors":"A. Guyonnet, S. Dagoret-Campagne, N. Mondrik","doi":"10.1142/s2251171719500132","DOIUrl":"https://doi.org/10.1142/s2251171719500132","url":null,"abstract":"Ground-based astronomy has to correct astronomical observations from the impact of the atmospheric transparency and its variability. The current objective of several observatories is to achieve a sub-percent-level monitoring of atmospheric transmission. A promising approach has been to combine internal calibration of the observations with various external meteorological data sources, upon availability and depending on quality. In this paper we investigate the use of the NASA Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) which is a general circulation model (GCM) and data assimilation system that renders freely available for any given site, at any time, all the parameters constraining atmospheric transmission. This paper demonstrates the extraction of the relevant atmospheric parameters for optical astronomy at two sites: Mauna Kea in Hawaii and Cerro Tololo International Observatory in Chile. The temporal variability for the past eight years (annual, overnight, and hourly) as well as the spatial gradients of ozone, precipitable water vapor, and aerosol optical depth are presented and their respective impacts on the atmospheric transparency are analyzed.","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":" ","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44548811","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-05-29DOI: 10.1142/S2251171719500028
C. Grava, T. Greathouse, K. Retherford, M. Davis, G. Gladstone, D. Kaufmann, A. Egan
Micro-Channel Plate (MCP) detectors can suffer from a form of degradation known as gain sag in regions with significant fluence. We have developed a method to recover the total Lyman-Alpha (Ly-[Formula: see text]) emission line (121.6[Formula: see text]nm) flux for the Lyman-Alpha Mapping Project (LAMP) UV imaging spectrograph onboard of the Lunar Reconnaissance Orbiter (LRO), where gain sag issues are important. The constant ratio between the Ly-[Formula: see text] emission line and its ghost image at shorter wavelengths allows for a useful correction factor for the true flux at the Ly-[Formula: see text] region of the detector. A similar method could be used in other spectrographs whenever a ghost image of sufficient brightness is present.
{"title":"A Method to Retrieve the Total Flux at Lyman-Alpha in Micro-Channel-Plate Detectors Affected by Gain Sag: Application to the LAMP UV Imaging Spectrograph Onboard the Lunar Reconnaissance Orbiter","authors":"C. Grava, T. Greathouse, K. Retherford, M. Davis, G. Gladstone, D. Kaufmann, A. Egan","doi":"10.1142/S2251171719500028","DOIUrl":"https://doi.org/10.1142/S2251171719500028","url":null,"abstract":"Micro-Channel Plate (MCP) detectors can suffer from a form of degradation known as gain sag in regions with significant fluence. We have developed a method to recover the total Lyman-Alpha (Ly-[Formula: see text]) emission line (121.6[Formula: see text]nm) flux for the Lyman-Alpha Mapping Project (LAMP) UV imaging spectrograph onboard of the Lunar Reconnaissance Orbiter (LRO), where gain sag issues are important. The constant ratio between the Ly-[Formula: see text] emission line and its ghost image at shorter wavelengths allows for a useful correction factor for the true flux at the Ly-[Formula: see text] region of the detector. A similar method could be used in other spectrographs whenever a ghost image of sufficient brightness is present.","PeriodicalId":45132,"journal":{"name":"Journal of Astronomical Instrumentation","volume":" ","pages":""},"PeriodicalIF":1.3,"publicationDate":"2019-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1142/S2251171719500028","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49415020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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