Journal articles on the topic 'Spatial photometry'
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Liu, Long, Yun Cui Zhang, and Jun Xiao. "The Influencing Factor Analyses of Narrow Beam LED Luminaire Performance Test." Advanced Materials Research 694-697 (May 2013): 3283–86. http://dx.doi.org/10.4028/www.scientific.net/amr.694-697.3283.
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The beam angle of the luminaire is an important factor to influence testing method. This paper mainly discusses the narrow beam luminaire test methods, especially luminaires space photometric, chromaticity characteristic test method. The factors step length and test time which influence spatial distribution photometer are analyzed. An example is introduced which show how to set electrical parameter, photometry parameter test efficiency for a narrow beam LED luminaire.
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Tinbergen, J. "Array Polarimetry and Optical-Differencing Photometry." Symposium - International Astronomical Union 167 (1995): 197–205. http://dx.doi.org/10.1017/s0074180900056448.
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Array detectors have improved the efficiency of optical polarimetry sufficiently for this technique to become part of the standard arsenal of observational facilities. However, we could gain even more: spatially-differentiating photometry can be implemented as an option of array Polarimeters and low-noise, high-frame-rate array detectors will allow extremely high precision both in polarimetry and in such differentiating photometry. The latter would be valuable for analyzing many kinds of optical or infrared images of very low contrast; the essence of the technique is to use optical (and extremely stable) means to produce the spatial derivative of the flux image, in the form of a polarization image which is then presented to a “standard” array polarimeter. The polarimeter should incorporate a polarization modulator of sufficient quality for the photometric application in mind. If developed properly, using a state-of-the-art array detector and the most sensitive type of polarization modulator (stress-birefringence), optical differencing will allow levels of relative photometric precision not otherwise obtainable. With the optical differencing option taken out of the beam, the same instrument can be used for high-quality polarimetry.
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Bezugla, Natalia, Serhii Poluectov, Vladyslav Chornyi, and Mikhail Bezuglyi. "MONTE CARLO SIMULATION OF LIGHT SCATTERING IN HUMAN SKIN LAYERS BY SPATIAL PHOTOMETRY METHODS." Bulletin of Kyiv Polytechnic Institute. Series Instrument Making, no. 61(1) (June 30, 2021): 91–100. http://dx.doi.org/10.20535/1970.61(1).2021.237112.
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The ability to register and analyze the spatial distribution of light scattered within the full solid angle is the basis for the development and improvement of information-measuring systems and software and hardware complexes for problems of optical biomedical diagnostics. The greatest contribution to light scattering at non-invasive methods of biomedical research are made by the layers of human skin, affecting the depth of probing and the resolution of diagnostic systems. The significant individual variability of the optical properties of biological tissues does not allow practically (clinically) assessing their effect on the light scattering characteristics; therefore, the use of methods for modeling the optical radiation propagation in media in the measuring tools functioning context makes it possible to provide such a prognostic analysis. The goal of this work is a comparative evaluation of the results of the light propagation in human skin layers by Monte Carlo simulation using information-measuring systems of a biomedical photometer with ellipsoidal reflectors and a goniophotometer.
The Monte Carlo simulation results of light scattering in dermis and epidermis at a wavelength of 632.8 nm using spatial photometry methods and the "BT_Mod" software, as well as coordinates, direction, and statistical weight of photons, allows the ray-tracing in a biomedical photometer with ellipsoidal reflectors are presented in this work.
As a result of modeling, graphs of the dependence of optical coefficients (transmission T, diffuse reflection Rd, and absorption A) for the studied tissues of various thicknesses on the value of the scattering anisotropy factor were obtained, as well as photometric images of the second focal plane of ellipsoidal reflectors when receiving a scattering spot in reflected and transmitted light. Diagrams of the averaged scattering indicatrix at three thicknesses of the epidermis and dermis were obtained for a set of biophysically significant values of the scattering anisotropy factor, based on which the integral distribution of the photons statistical weight in diffuse scattered light was analyzed. A quantitative assessment of the illuminance level of images is carried out according to the zone analysis principles in photometry by ellipsoidal reflectors. The resulting graphs of the illuminance dependence the external and middle rings of photometric images in reflected and transmitted light.
The results of the research make it possible to analyze the spatial distribution of light scattered by the human skin layers (epidermis and dermis) within the full solid angle, which can be used in problems of optical dosimetry and medical imaging in diagnostic, endoscopic, and therapeutic methods of biophotonics.
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Xiao, Kai, and Haibo Yuan. "Validation and Improvement of the Pan-STARRS Photometric Calibration with the Stellar Color Regression Method." Astronomical Journal 163, no. 4 (March 22, 2022): 185. http://dx.doi.org/10.3847/1538-3881/ac540a.
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Abstract As one of the best ground-based photometric data set, Pan-STARRS1 (PS1) has been widely used as the reference to calibrate other surveys. In this work, we present an independent validation and recalibration of the PS1 photometry using spectroscopic data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR7, and photometric data from the corrected Gaia Early Data Release 3 (EDR3) with the Stellar Color Regression (SCR) method. Using per band typically a total of 1.5 million LAMOST-PS1-Gaia stars as standards, we show that the PS1 photometric calibration precisions in the grizy filters are around 4 ∼ 5 mmag when averaged over 20′ regions. However, significant large- and small-scale spatial variation of magnitude offset, up to over 1%, probably caused by the calibration errors in the PS1, are found for all the grizy filters. The calibration errors in different filters are uncorrelated, and are slightly larger for the g and y filters. We also detect moderate magnitude-dependent errors (0.005, 0.005, 0.005, 0.004, 0.003 mag per magnitude in the 14–17 mag range for the grizy filters, respectively) in the PS1 photometry by comparing with the Gaia EDR3 and other catalogs. The errors are likely caused by the systematic uncertainties in the PSF magnitudes. We provide two-dimensional maps to correct for such magnitude offsets in the LAMOST footprint at different spatial resolutions from 20′ to 160′. The results demonstrate the power of the SCR method in improving the calibration precision of wide-field surveys when combined with the LAMOST spectroscopy and Gaia photometry.
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Thanjavur, Karun, Željko Ivezić, Sahar S. Allam, Douglas L. Tucker, J. Allyn Smith, and Stephen Gwyn. "Photometric cross-calibration of the SDSS Stripe 82 Standard Stars catalogue with Gaia EDR3, and comparison with Pan-STARRS1, DES, CFIS, and GALEX catalogues." Monthly Notices of the Royal Astronomical Society 505, no. 4 (May 22, 2021): 5941–56. http://dx.doi.org/10.1093/mnras/stab1452.
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ABSTRACT We extend the SDSS Stripe 82 Standard Stars catalogue with post-2007 SDSS imaging data. This improved version lists averaged SDSS ugriz photometry for nearly a million stars brighter than r ∼ 22 mag. With 2–3 times more measurements per star, random errors are 1.4–1.7 times smaller than in the original catalogue, and about three times smaller than for individual SDSS runs. Random errors in the new catalogue are $\lesssim$0.01 mag for stars brighter than 20.0, 21.0, 21.0, 20.5, and 19.0 mag in u, g, r, i, and z-bands, respectively. We achieve this error threshold by using the Gaia Early Data Release 3 (EDR3) Gmag photometry to derive grey photometric zeropoint corrections, as functions of RA and Declination, for the SDSS catalogue, and use the Gaia BP–RP colour to derive corrections in the ugiz bands, relative to the r-band. The quality of the recalibrated photometry, tested against Pan-STARRS1, DES, CFIS, and GALEX surveys, indicates spatial variations of photometric zeropoints ≦ 0.01 mag (rms), with typical values of 3–7 millimag in the RA, and 1–2 millimag in the Declination directions, except for $\lesssim$6 millimag scatter in the u-band. We also report a few minor photometric problems with other surveys considered here, including a magnitude-dependent ∼0.01 mag bias between 16 ≤ GGaia ≤ 20 in the Gaia EDR3. Our new, publicly available catalogue offers robust calibration of ugriz photometry below 1 per cent level, and will be helpful during the commissioning of the Vera C. Rubin Observatory Legacy Survey of Space and Time.
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Rau, M. M., C. B. Morrison, S. J. Schmidt, S. Wilson, R. Mandelbaum, Y.-Y. Mao, David Alonso, et al. "A composite likelihood approach for inference under photometric redshift uncertainty." Monthly Notices of the Royal Astronomical Society 509, no. 4 (November 12, 2021): 4886–907. http://dx.doi.org/10.1093/mnras/stab3290.
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ABSTRACT Obtaining accurately calibrated redshift distributions of photometric samples is one of the great challenges in photometric surveys like LSST, Euclid, HSC, KiDS, and DES. We present an inference methodology that combines the redshift information from the galaxy photometry with constraints from two-point functions, utilizing cross-correlations with spatially overlapping spectroscopic samples, and illustrate the approach on CosmoDC2 simulations. Our likelihood framework is designed to integrate directly into a typical large-scale structure and weak lensing analysis based on two-point functions. We discuss efficient and accurate inference techniques that allow us to scale the method to the large samples of galaxies to be expected in LSST. We consider statistical challenges like the parametrization of redshift systematics, discuss and evaluate techniques to regularize the sample redshift distributions, and investigate techniques that can help to detect and calibrate sources of systematic error using posterior predictive checks. We evaluate and forecast photometric redshift performance using data from the CosmoDC2 simulations, within which we mimic a DESI-like spectroscopic calibration sample for cross-correlations. Using a combination of spatial cross-correlations and photometry, we show that we can provide calibration of the mean of the sample redshift distribution to an accuracy of at least 0.002(1 + z), consistent with the LSST-Y1 science requirements for weak lensing and large-scale structure probes.
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DENIEL, Jean-Marc. "Computing spatial distribution of tube and louvre luminaires efficiency from their description." International Journal of Sustainable Lighting 22, no. 1 (June 15, 2020): 12–27. http://dx.doi.org/10.26607/ijsl.v22i1.94.
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Lighting computation requires photometry data that are not always available. Lacking photometry data limits lighting study to in situ measurement, luminaire measurement or use of similar luminaire photometry. This is not satisfactory, neither for convenience nor cost and accuracy reasons. Fitting the spatial distribution of luminaire efficiency to their description would allow lighting computations in this kind of situation. An efficiency spatial distribution model is proposed for grid and louvre tube luminaires, taking optic width, louvre between-axis and gloss as parameters. It is constructed over 12 measured efficiency spatial distributions and the corresponding luminaire descriptors. Even if optic and louvre gloss cannot be differentiated, this model fits to measurements and allows for computed irradiance close to experiments within −5% to +19%. In addition, luminaire descriptors can freely vary inside their experimental range and even be extrapolated.
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Caldwell, John A. R., and C. David Laney. "Cepheids in the Magellanic Clouds." Symposium - International Astronomical Union 148 (1991): 249–57. http://dx.doi.org/10.1017/s0074180900200545.
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Cepheid variables provide a key to understanding the structure and distance of the Magellanic Clouds, as well as providing accurate reddenings there. Recent major observing programs have continually expanded the data base of photometry and velocities. It is important to try to reconcile the plethora of Cepheid data into a consonant picture of the three-dimensional spatial structure of the Clouds and to compare in a consistent manner the bulk Cloud distance moduli found by several photometric methods.
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Bezuglyi, Mikhail, and Natalia Bezuglaya. "Raman Spectroscopy Principles for in vivo Diagnostic by Ellipsoidal Reflectors." Electrical, Control and Communication Engineering 15, no. 1 (September 1, 2019): 39–46. http://dx.doi.org/10.2478/ecce-2019-0006.
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AbstractThe paper presents the analysis of the functional abilities of measurement tools with ellipsoidal reflectors for Raman spectroscopy. The investigated structural scheme of the setup is intended for use in Raman spectroscopy in vivo by ellipsoidal reflectors. The setup can be used as a prototype for development of a device for non-invasive control of sugar level. Additionally, the investigation demonstrates the efficiency of ellipsoidal photometry method for registration of Raman scattering signal on test-solutions. The testing was performed for different sugar concentrations with the laser radiation wavelength 980 nm. In addition, the selecting principles of laser radiation source parameters (including beam diameter and power) were investigated. During the research, the data about spatial distribution of the backscattered light in human shoulder and finger tissues during photometry by ellipsoidal reflectors were received. The procedure involves application of Monte Carlo simulation. The dependency of the external and middle ring illuminance of photometric images on the diameter and power of the laser beam is represented based on the zone analysis.
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Mimica, P., and K. Pavlovski. "Reconstruction of an Accretion Disk Image in AU Mon from CoRoT Photometry." Proceedings of the International Astronomical Union 7, S282 (July 2011): 63–64. http://dx.doi.org/10.1017/s1743921311026901.
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AbstractThe long-period binary system AU Mon was photometrically observed on-board the CoRoT satellite in a continuous run of almost 60 days long which has covered almost 5 complete cycles. Unprecedented sub milimag precision of CoRoT photometry reveals all complexity of its light variations in this, still active mass-transfer binary system. We present images of an accretion disk reconstructed by eclipse mapping, and an optimization of intensity distribution along disk surface. Time resolution and accurate CoRoT photometric measurements allow precise location of spatial distribution of ‘hot’ spots on the disk, and tracing temporal changes in their activity. Clumpy disk structure is similar to those we detected early for another W Serpentis binary W Cru (Pavlovski, Burki & Mimica, 2006, A&A, 454, 855).
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Aurière, M., J. P. Cordoni, O. Le Fèvre, and A. Terzan. "A High Spatial Resolution Investigation of the Core of Some Dynamically Evolved Globular Clusters." Symposium - International Astronomical Union 113 (1985): 63–64. http://dx.doi.org/10.1017/s0074180900147217.
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We present a high spatial resolution photographic study of the core of some concentrated globular clusters (F.W.H.M. of averaged star intensity profiles reaches 0″.5 on the best plates). Good plates of M 79, M 53, M 3, M 5, M 13, M 92, NGC 6397, M 15, M 2 and M 30 were obtained (Aurière and Cordoni, 1983, Astron. Astrophys. Suppl. Ser. 52, 383 and references therein). The observations are mainly obtained at the 2 m and 1 m Cassegrain telescopes of Pic-du-Midi Observatory. The high spatial resolution of our plates enables us to achieve stellar photometry, at least for the bright stars, in these overcrowded regions. Surface photometry is also obtained.
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Hodgkin, S. T., D. L. Harrison, E. Breedt, T. Wevers, G. Rixon, A. Delgado, A. Yoldas, et al. "Gaia Early Data Release 3." Astronomy & Astrophysics 652 (August 2021): A76. http://dx.doi.org/10.1051/0004-6361/202140735.
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Context. Since July 2014, the Gaia mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky. Aims. We present the Gaia Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by Gaia. Methods. We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to Gaia and (2) Gaia sources which have undergone a significant brightening or fading. Validation of the Gaia transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours. Results. We show that the Gaia Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae, CE = 0.46, is dominated by the Gaia scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is CI = 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec. Conclusions. The per-transit photometry for Gaia transients is precise to 1% at G = 13, and 3% at G = 19. The per-transit astrometry is accurate to 55 mas when compared to Gaia DR2. The Gaia Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge.
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Seidensticker, K. J., and Th Schmidt-Kaler. "Extinction Maps of Dust Clouds from Surface Photometry." Symposium - International Astronomical Union 139 (1990): 239–40. http://dx.doi.org/10.1017/s0074180900240795.
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We present a new method, based on surface photometry, which allows one to make the spatial resolution of extinction maps of dark clouds as fine as necessary. Applying this technique to the Coalsack (l = 302°, b = 0°), we derived an extinction map and the dust mass MD = (62 ± 25) M⊙. The density was found to vary ρ ~ r−0.8, typical for stable clouds.
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Gusev, Alexander S., and Elena V. Shimanovskaya. "Spatial regularity of the young stellar population in the ring of NGC 6217." Astronomy & Astrophysics 640 (July 31, 2020): L7. http://dx.doi.org/10.1051/0004-6361/202038530.
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The relative contribution of various physical processes to the spatial and temporal distribution of molecular clouds and star-forming regions in the disks of galaxies has not yet been the subject of extensive study. Investigating the spatial regularity in the distribution of the young stellar population in spiral and ring structures is a good test for studying this contribution. In this paper, we look at the photometric properties of the ring and spiral arms in the barred spiral galaxy NGC 6217 based on an analysis using GALEX ultraviolet, optical UBVRI, and Hα surface photometry data. The ring in the galaxy is located near the corotation area. We found evidence of spatial regularity in the distribution of the young stellar population along the galaxy ring. The characteristic scale of spacing is about 700 pc. At the same time, we did not find a similar regularity in the distribution of the young stellar population along the spiral arms of NGC 6217. The spatial regularity in the concentration of young stellar groupings along spiral arms is a quite rare phenomenon and it has never previously been seen in galactic rings.
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Bratsolis, E., and M. Sigelle. "A spatial regularization method preserving local photometry for Richardson-Lucy restoration." Astronomy and Astrophysics 375, no. 3 (September 2001): 1120–28. http://dx.doi.org/10.1051/0004-6361:20010709.
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Allen, R. J., S. Sukumar, F. X. Hu, and P. C. Van Der Kruit. "Optical and Radio Surface Photometry of NGC 891." Symposium - International Astronomical Union 140 (1990): 223–24. http://dx.doi.org/10.1017/s0074180900190047.
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A general correlation between the radio and optical continuum surface brightness has been found in the edge-on galaxy NGC 891. This suggests that the relativistic electrons are produced/accelerated in the vicinity of evolved stars or stellar remnants which have a spatial distribution similar to old disk stars. In this picture, the magnetic field required for the synchrotron emission is carried up from the disk to high Z through instabilities and star-forming activity in the plane.
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Román, Javier, Ignacio Trujillo, and Mireia Montes. "Galactic cirri in deep optical imaging." Astronomy & Astrophysics 644 (November 27, 2020): A42. http://dx.doi.org/10.1051/0004-6361/201936111.
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The ubiquitous presence of Galactic cirri in deep optical images represents a major obstacle to study the low surface brightness features of extragalactic sources. To address this issue, we have explored the optical properties of cirri using g, r, i, and z bands in the Sloan Digital Sky Survey (SDSS) Stripe82 region. Using state-of-the-art, custom made, image processing techniques, including the modeling and removal of the instrumental scattered light produced by the stars, we managed to isolate the optical diffuse emission by the cirri, allowing their photometric characterization. We find that their optical colors are driven by the dust column density: The cirri become redder as their 100 μm emission increases. Remarkably, the optical colors of the Galactic cirri differ significantly from those of extragalactic sources, with a characteristic bluer r-i color for a given g-r, allowing one to detect these by using a simple color relation. Our results show the high potential of deep multi-band optical photometry, on its own, identifying the presence of cirri at a higher spatial resolution than those provided by far-infrared observations. The combination of very deep data and multi-band photometry (as the one produced by LSST and Euclid) would make it possible to build dust maps of unprecedented quality.
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WOOTEN, BILLY R., and BILLY R. HAMMOND. "Spectral Absorbance and Spatial Distribution of Macular Pigment Using Heterochromatic Flicker Photometry." Optometry and Vision Science 82, no. 5 (May 2005): 378–86. http://dx.doi.org/10.1097/01.opx.0000162654.32112.a1.
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Chen, J. S. "Wide Field Imaging and Photometry by 2k × 2k CCD." Symposium - International Astronomical Union 161 (1994): 17–19. http://dx.doi.org/10.1017/s0074180900046933.
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The Ford Aerospace 2048 × 2048 CCD with UV coating is used at the BAO 60/90 cm f/3 Schmidt telescope focal plane, giving a field-of-view of about one square degree and spatial resolution of 1.67 arcsecond per pixel. The paper reviews the following topics: 1) basic performance of the system; 2) anti-blooming technique for a large field CCD; 3) flat fielding for a large field CCD; 4) photometric properties of compressed images.
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Strantzalis, A., D. Hatzidimitriou, A. Zezas, V. Antoniou, S. Lianou, and S. Tsilia. "Discrete star formation events in the central bar of the Small Magellanic Cloud." Monthly Notices of the Royal Astronomical Society 489, no. 4 (September 11, 2019): 5087–97. http://dx.doi.org/10.1093/mnras/stz2540.
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ABSTRACT We present the results of the photometric analysis of a large part of the main body of the Small Magellanic Cloud. Using the 6.5m Magellan Telescope at the Las Campanas Observatory in Chile, we have acquired deep B and I images in four fields (0.44 deg each in diameter), yielding accurate photometry for 1068 893 stars down to 24th magnitude, with a spatial resolution of 0.20 arcsec per pixel. Colour–magnitude diagrams and (completeness-corrected) luminosity functions have been constructed, yielding significant new results that indicate at least two discrete star formation events over a period from 2.7 to 4 Gyr ago. Also, we have derived star formation rates as a function of look-back time and have found enhancements of SF between 4 and 6 Gyr and at younger ages.
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Linde, P., A. Ardeberg, and B. Gustafsson. "Old Structure – Young Stars The Stellar Content of the Centre of the LMC Bar." Symposium - International Astronomical Union 192 (1999): 108–11. http://dx.doi.org/10.1017/s0074180900203999.
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The history of star formation and chemical evolution are studied in the LMC Bar centre with the HST PC and WFC and uvby photometry. Using dedicated image processing, we secured high spatial resolution and photometric quality. We present colour magnitude diagrams (CMDs) from PC and WFC y and b data. The PC provides a CMD close to complete to V = 23.5, the WFC contributes favourable statistics on brighter stars. We find a population of stars seemingly around or younger than 0.2 Gyr comprising around 30% of the total amount of stars. Star formation seems to have decreased 3-0.2 Gyr ago. Older populations are aged 3–9 Gyr. Stars older than 10 Gyr seem rare if not absent. Our CMD morphology and, especially, our uvby metallicity index give [Me/H] close to −0.4, with older stars more and younger stars less metal poor.
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KATO, Mika, Megumi NUMAJIRI, Hideki YAMAGUCHI, Wataru IWAI, Katsuhiko SAKATA, Naoyuki SUZUKI, Naoya HARA, and Nozomu YOSHIZWA. "STUDY ON APPLICABILITY OF MEAN LUMINANCE BY IMAGE PHOTOMETRY AS SPATIAL BRIGHTNESS INDEX." Journal of Environmental Engineering (Transactions of AIJ) 84, no. 766 (2019): 1059–66. http://dx.doi.org/10.3130/aije.84.1059.
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Kapitza, H. G., G. McGregor, and K. A. Jacobson. "Direct measurement of lateral transport in membranes by using time-resolved spatial photometry." Proceedings of the National Academy of Sciences 82, no. 12 (June 1, 1985): 4122–26. http://dx.doi.org/10.1073/pnas.82.12.4122.
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Leščinskaitė, Alina, Rima Stonkutė, and Vladas Vansevičius. "Bright-red stars in the dwarf irregular galaxy Leo A." Proceedings of the International Astronomical Union 14, S344 (August 2018): 99–102. http://dx.doi.org/10.1017/s1743921318006427.
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AbstractWe analysed a population of bright-red (BR) stars in the dwarf irregular galaxy Leo A by using multicolour photometry data obtained with the Subaru/Suprime-Cam (B, V, R, I,Hα) and HST/ACS (F475W & F814W) instruments. In order to separate the Milky Way (MW) and Leo A populations of red stars, we developed a photometric method, which enabled us to study the spatial distribution of BR stars within the Leo A galaxy.We found a significant difference in the scale-length (S-L) of radial distributions of the “young” and “old” red giant branch (RGB) stars – 0′.82 ± 0′.04 and 1′53 ± 0′.03, respectively. Also, we determined the S-L of BR stars of 0′.85 ± 0′.05, which closely matches that of the “young” RGB stars. Additionally, we found a sequence of peculiar RGB stars and 8 dust-enshrouded stars in the Leo A galaxy.
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Rufeng, Li, Ye Binxum, Chen Hailin, Liu Shaohua, Deng Bailian, Ma Jagu, H. A. Hill, and P. H. Oglesby. "Solar Oscillations Instrument at an Infrared Wavelength of 1.6 μm at Yunnan Observatory." Symposium - International Astronomical Union 154 (1994): 283–86. http://dx.doi.org/10.1017/s0074180900124544.
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A photometric solar seismograph, as part of an international network, was installed at Yunnan Observatory, the Chinese Academy of Sciences, and put into operation in the spring of 1991. This instrument is used to detect solar oscillations by measuring the continuum radiation intensity on the solar disk with a spatial resolution of 50 arcsec, in heliocentric coordinates, for research on p-modes and g-modes when l < 50, where l is the angular degree of the eigenfunction. The solar oscillations can be observed simultaneously at two wavelengths of the detector with a sensitivity of 10 of the average intensity. This paper reports on the optical system of the instrument. Also introduced in this paper is the compensation system for the noise signals produced by the changes in the transparency of the Earth's atmosphere. This is based on solar photometry at wavelengths of 0.55 mm and 1.6 mm.
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Young, Andrew T. "Choosing Filters to Make CCD Photometry Transformable to Other Detectors." Symposium - International Astronomical Union 167 (1995): 145–56. http://dx.doi.org/10.1017/s0074180900056382.
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Transforming CCD data is difficult. Until recently, the general transformation problem was so poorly understood that there were no established design criteria. Now, the Hilbert-space approach to photometry tells us to match the standard passbands in the least-squares sense.Unfortunately, the spectral responsivities of CCDs vary much more than do conventional detectors, and must be known to design filters. Each individual chip generally requires its own set of filters, if results are to be better than second-rate. Even so, spatial variations in spectral response limit the accuracy that can be reached, unless color terms are determined for individual pixels. Such CCD calibration problems involve the generally neglected optical properties of CCDs and the systems in which they are used.Large observatories will have to establish calibration laboratories, and to abandon the common practice of moving “standard” filter sets from one instrument to another. Smaller institutions will need to purchase the services of such calibration laboratories if they are to produce accurate CCD photometry. These are major changes in the way astronomers are accustomed to working; but such changes are necessary to stem the backlash developing against CCD photometry.
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Narloch, W., G. Pietrzyński, W. Gieren, A. E. Piatti, M. Górski, P. Karczmarek, D. Graczyk, et al. "Metallicities and ages for 35 star clusters and their surrounding fields in the Small Magellanic Cloud." Astronomy & Astrophysics 647 (March 2021): A135. http://dx.doi.org/10.1051/0004-6361/202039623.
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Aims. In this work we study 35 stellar clusters in the Small Magellanic Cloud (SMC) in order to provide their mean metallicities and ages. We also provide mean metallicities of the fields surrounding the clusters. Methods. We used Strömgren photometry obtained with the 4.1 m SOAR telescope and take advantage of (b − y) and m1 colors for which there is a metallicity calibration presented in the literature. Results. The spatial metallicity and age distributions of clusters across the SMC are investigated using the results obtained by Strömgren photometry. We confirm earlier observations that younger, more metal-rich star clusters are concentrated in the central regions of the galaxy, while older, more metal-poor clusters are located farther from the SMC center. We construct the age–metallicity relation for the studied clusters and find good agreement with theoretical models of chemical enrichment, and with other literature age and metallicity values for those clusters. We also provide the mean metallicities for old and young populations of the field stars surrounding the clusters, and find the latter to be in good agreement with recent studies of the SMC Cepheid population. Finally, the Strömgren photometry obtained for this study is made publicly available.
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Ruiz, A., A. Georgakakis, S. Gerakakis, R. Saxton, P. Kretschmar, A. Akylas, and I. Georgantopoulos. "The RapidXMM upper limit server: X-ray aperture photometry of the XMM-Newton archival observations." Monthly Notices of the Royal Astronomical Society 511, no. 3 (January 31, 2022): 4265–84. http://dx.doi.org/10.1093/mnras/stac272.
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ABSTRACT This paper presents the construction of the RapidXMM database that is available through the XMM-Newton Science Archive and offers access to upper limits and aperture photometry across the field of view of the XMM-Newton Pointed and Slew Survey observations. The feature of RapidXMM is speed. It enables the fast retrieval of X-ray upper limits and photometry products in three energy bands (0.2–2, 2–12, and 0.2–12 keV) for large numbers of input sky positions. This is accomplished using the Hierarchical Equal Area Iso Latitude pixelation of the sphere (HEALPix). The pre-calculated upper-limits and associated X-ray photometry products are reprojected into the HEALPix grid of cells before being ingested into the RapidXMM database. This results in tables of upper limits and aperture photometry within HEALPix cells of size ≈3 arcsec (Pointed observations) and 6 arcsec (Slew Survey). The database tables are indexed by the unique integer number of the HEALPix cells. This reduces spatial nearest-neighbour queries by sky position to an integer-matching exercise and significantly accelerates the retrieval of results. We describe in detail the processing steps that lead from the science products available in the XMM-Newton archive to a database optimized for sky queries. We also present two simple show-case applications of RapidXMM for scientific studies – searching for variable X-ray sources and stacking analysis of X-ray faint populations.
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Fulmer, Leah M., John S. Gallagher, Wolf-Rainer Hamann, Lida M. Oskinova, and Varsha Ramachandran. "Testing massive star evolution, star-formation history, and feedback at low metallicity." Astronomy & Astrophysics 633 (January 2020): A164. http://dx.doi.org/10.1051/0004-6361/201834314.
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Context. The supergiant ionized shell SMC-SGS 1 (DEM 167), which is located in the outer Wing of the Small Magellanic Cloud (SMC), resembles structures that originate from an energetic star-formation event and later stimulate star formation as they expand into the ambient medium. However, stellar populations within and surrounding SMC-SGS 1 tell a different story. Aims. We present a photometric study of the stellar population encompassed by SMC-SGS 1 in order to trace the history of such a large structure and its potential influence on star formation within the low-density, low-metallicity environment of the SMC. Methods. For a stellar population that is physically associated with SMC-SGS 1, we combined near-ultraviolet (NUV) photometry from the Galaxy Evolution Explorer with archival optical (V-band) photometry from the ESO Danish 1.54 m Telescope. Given their colors and luminosities, we estimated stellar ages and masses by matching observed photometry to theoretical stellar isochrone models. Results. We find that the investigated region supports an active, extended star-formation event spanning ∼25−40 Myr ago, as well as continued star formation into the present. Using a standard initial mass function, we infer a lower bound on the stellar mass from this period of ∼3 × 104 M⊙, corresponding to a star-formation intensity of ∼6 × 10−3 M⊙ kpc−2 yr−1. Conclusions. The spatial and temporal distributions of young stars encompassed by SMC-SGS 1 imply a slow, consistent progression of star formation over millions of years. Ongoing star formation, both along the edge and interior to SMC-SGS 1, suggests a combined stimulated and stochastic mode of star formation within the SMC Wing. We note that a slow expansion of the shell within this low-density environment may preserve molecular clouds within the volume of the shell, leaving them to form stars even after nearby stellar feedback expels local gas and dust.
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Gruenstein, Eric, and Jesus Luna. "An inexpensive, easy to use video imaging system for intracellular Ca2+ and quantitative fluorescence microscopy." Proceedings, annual meeting, Electron Microscopy Society of America 51 (August 1, 1993): 620–21. http://dx.doi.org/10.1017/s0424820100148939.
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Fura-2 is the most commonly used member of a family of calcium sensitive flourescent dyes that allows the measurement of intracellular free calcium (Cai by dual excitation fluorimetry. The use of this dye in conjunction with video imaging microscopy permits visualization of changes in Cai with a high degree of spatial resolution. This resolution in turn allows the detection of Cai gradients, waves, and other localized cellular responses not easily detected by photometric techniques. Despite these advantages, most published reports have utilized photometry rather than imaging, due largely to the higher cost and greater complexity of use of the latter technique. With these problems in mind, we have developed a turnkey calcium imaging system that is both inexpensive and simple enough to use that it can be mastered in 2-3 hours.Data showing the distribution of free Ca2+ in the cytoplasm of a quiescent human fibroblast and the kinetics of stimulation of these cells with mitogens are illustrated on the next page.
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Danilova, M., C. Chan, and J. Mollon. "Individual differences in cone ratio: Measurements by counterphase modulation photometry and by spatial acuity." Journal of Vision 11, no. 15 (December 21, 2011): 33. http://dx.doi.org/10.1167/11.15.33.
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Li, Yamin, Lijie Zhan, Yang wang, Ruru Chen, Xiaowei Yang, Xiaoting Wu, Yijun Wang, Hongda Chen, Chun Xu, and Weihua Pei. "Improve the spatial resolution of fiber photometry by μLED linear array for fluorescence detection." Sensors and Actuators A: Physical 331 (November 2021): 112948. http://dx.doi.org/10.1016/j.sna.2021.112948.
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Greggio, L., M. Gullieuszik, R. Falomo, D. Fantinel, and M. Uslenghi. "Properties of high z galaxies in the ELTs era." Proceedings of the International Astronomical Union 11, S319 (August 2015): 21. http://dx.doi.org/10.1017/s1743921315009898.
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The extraordinary sensitivity and spatial resolution of the future extremely large telescopes will allow us to extensively characterize the photometrical and structural properties of high redshift galaxies in spite of their very small size. With such future facilities it will be possible to derive both accurate photometry and detailed morphology of very distant galaxies that are mandatory to tackle fundamental problems on the processes of galaxy formation and evolution.
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Maíz Apellániz, J., M. Pantaleoni González, R. H. Barbá, P. García-Lario, and F. Nogueras-Lara. "Galactic extinction laws – I. A global NIR analysis with 2MASS photometry." Monthly Notices of the Royal Astronomical Society 496, no. 4 (June 22, 2020): 4951–63. http://dx.doi.org/10.1093/mnras/staa1790.
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ABSTRACT We have started an ambitious program to determine if the full diversity of extinction laws is real or if some of it is due to calibration or methodological issues. Here we start by analysing the information on near-infrared (NIR) extinction in a Two Micron All-Sky Survey (2MASS) stellar sample with good quality photometry and very red colours. We calculate the extinction at 1 μm, A1, and the power-law exponent, α (Aλ = A1λ−α), for the 2MASS stars located in the extinction trajectory in the H − K versus J − H plane expected for red giants with A1 > 5 mag. We test the validity of the assumption about the nature of those stars, whether a single or multiple values of α are needed, and the spatial variations of the results. Most (∼83 per cent) of those stars can indeed be explained by high-extinction red giants and the rest are composed of extinguished asymptotic giant branch (AGB) stars (mostly O-rich), blended sources, and smaller numbers of other objects, a contaminant fraction that can be reduced with the help of Gaia Data Release 2 (DR2) data. Galactic red giants experience a NIR extinction with α ∼ 2.27 and an uncertainty of a few hundredths of a magnitude. There is no significant spread in α even though our sample is widely distributed and has a broad range of extinctions. Differences with previous results are ascribed to the treatment of non-linear photometric effects and/or the contaminant correction. Future research should concentrate in finding the correct functional form for the NIR extinction law. In the appendix, we detail the treatment of non-linear photometric effects in the 2MASS bands.
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Kvernadze, Teimuraz M. "The Stellar Structure of the Orion Spiral ARM in Selected Directions. I. The Galactic Anticenter." International Astronomical Union Colloquium 148 (1995): 384–87. http://dx.doi.org/10.1017/s0252921100022247.
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To investigate the spatial distribution of various stellar groups in the Hertzsprung-Russell diagram, it is necessary to have homogeneous observational data of MK spectral classification and photometry. This enables us to perform some statistical analyses with sufficient accuracy.This paper reports BV photographic photometry of about 700 stars complete to mV = 12, in the direction of galactic anticenter with (l,b) = (169°, −12.4°), (178°, −2.4°), (184°, 8.9°). For the MK spectral data we used the catalogue by Bartaya and Kharadze (1992), which contains spectral and luminosity classes of 6042 stars in Kapteyn Areas Nos. 44–67. The observational data for this catalogue were obtained using the Abastumani Astrophysical Observatory 70 cm meniscus telescope and an 8°objective prism with dispersion 166 Åmm−1 near Hγ. The errors in classification are equal to ± 0.6 spectral subclasses and ± 0.5 luminosity classes, with a limiting magnitude of mV = 12.5.
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Kleinmann, S. G. "The Spatial, Temporal, and Photometric Properties of AGB Stars." International Astronomical Union Colloquium 106 (May 1993): 13–25. http://dx.doi.org/10.1017/s0252921100062576.
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The Two Micron Sky Survey (Neugebauer & Leighton 1969;TMSS) provides a census of AGB stars which is relatively insensitive to interstellar or circumstellar reddening, temporal variations, or differences in photospheric temperature. This paper summarizes results from recent analyses of all carbon, S type, and mass-losing M stars in the TMSS, including local surface densities, scale heights, and mass loss rates. All three groups are concentrated toward the plane; the mass-losing M stars appear least concentrated toward the plane but most strongly concentrated toward the galactic center. Results from the IRAS survey were used to determine the range of infrared colors of stars in each class, and to estimate their mass loss rates. Carbon stars have relatively higher 60 μm flux densities than oxygen-rich stars, and have relatively higher mass loss rates. The total mass loss rate is dominated by a small fraction of the stars in this sample. IRAS photometry and IRAS Low Resolution Spectometer data do not unambiguously distinguish carbon-rich and oxygen-rich stars in this sample. Future searches for stars with the greatest mass loss rates might concentrate on sources found to be variable in the IRAS survey, since a large fraction of the TMSS stars with the most massive envelopes are known Miras or infrared variables.
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Ivanova, Oleksandra, Igor Luk’yanyk, Ludmilla Kolokolova, Himadri Sekhar Das, Marek Husárik, Vera Rosenbush, Viktor Afanasiev, Ján Svoreň, Nikolai Kiselev, and Vadim Krushinsky. "Photometry, spectroscopy, and polarimetry of distant comet C/2014 A4 (SONEAR)." Astronomy & Astrophysics 626 (June 2019): A26. http://dx.doi.org/10.1051/0004-6361/201935077.
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Context. The study of distant comets, which are active at large heliocentric distances, is important for a better understanding of their physical properties and mechanisms of long-lasting activity. Aims. We analyzed the dust environment of the distant comet C/2014 A4 (SONEAR), with a perihelion distance near 4.1 au, using comprehensive observations obtained by different methods. Methods. We present an analysis of spectroscopy, photometry, and polarimetry of comet C/2014 A4 (SONEAR), which were performed on November 5–7, 2015, when its heliocentric distance was 4.2 au and phase angle was 4.7°. Long-slit spectra and photometric and linear polarimetric images were obtained using the focal reducer SCORPIO-2 attached to the prime focus of the 6 m telescope BTA (SAO RAS, Russia). We simulated the behavior of color and polarization in the coma presenting the cometary dust as a set of polydisperse polyshapes rough spheroids. Results. No emission features were detected in the 3800–7200 Å wavelength range. The continuum showed a reddening effect with the normalized gradient of reflectivity 21.6 ± 0.2% per 1000 Å within the 4650–6200 Å wavelength region. The fan-like structure in the sunward hemisphere was detected. The radial profiles of surface brightness differ for r-sdss and g-sdss filters, indicating a predominance of submicron and micron-sized particles in the cometary coma. The dust color (g–r) varies from 0.75 ± 0.05m to 0.45 ± 0.06m along the tail. For an aperture radius near 20 000 km, the dust productions in various filters were estimated as Afρ = 680 ± 18 cm (r-sdss) and 887 ± 16 cm (g-sdss). The polarization map shows spatial variations in polarization over the coma from about −3% near the nucleus to −8% at a cometocentric distance of about 150 000 km. Our simulations show that the dust particles are dominated (or covered) by ice and tholin-like organics. Spatial changes in the color and polarization can be explained by particle fragmentation.
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Herpich, F. R., C. E. Ferreira Lopes, R. K. Saito, D. Minniti, A. Ederoclite, T. S. Ferreira, and M. Catelan. "VVV survey near-infrared colour catalogue of known variable stars." Astronomy & Astrophysics 647 (March 2021): A169. http://dx.doi.org/10.1051/0004-6361/201834356.
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Context. The Vista Variables in the Via Lactea (VVV) near-infrared variability survey explores some of the most complex regions of the Milky Way bulge and disk in terms of high extinction and high crowding. Aims. We add a new wavelength dimension to the optical information available at the American Association of Variable Star Observers International Variable Star Index (VSX-AAVSO) catalogue to test the VVV survey near-infrared photometry to better characterise these objects. Methods. We cross-matched the VVV and the VSX-AAVSO catalogues along with Gaia Data Release 2 photometry and parallax. Results. We present a catalogue that includes accurate individual coordinates, near-infrared magnitudes (ZYJHKs), extinctions AKs, and distances based on Gaia parallaxes. We also show the near-infrared CMDs and spatial distributions for the different VSX types of variable stars, including important distance indicators, such as RR Lyrae, Cepheids, and Miras. By analysing the photometric flags in our catalogue, we found that about 20% of the stars with measured and verified variability are flagged as non-stellar sources, even when they are outside of the saturation and/or noise regimes. Additionally, we pair-matched our sample with the VIVA catalogue and found that more than half of our sources are missing from the VVV variability list, mostly due to observations with low signal-to-noise ratio or photometric problems with a low percentage due to failures in the selection process. Conclusions. Our results suggest that the current knowledge of the variability in the Galaxy is biased to nearby stars with low extinction. The present catalogue also provides the groundwork for characterising the results of future large variability surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time in the highly crowded and reddened regions of the Galactic plane, as well as follow-up campaigns for characterising specific types of variables. The analysis of the incorrectly flagged stars can be used to improve the photometric classification of the VVV data, allowing us to expand the amount of data considered useful for science purposes. In addition, we provide a list of stars that are missed by the VIVA procedures for which the observations are good and which were missed due to some failure in the VIVA selection process.
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Xu, Fukun, Shenghong Gu, and Panogiotis Ioannidis. "Starspot evolution, differential rotation, and correlation between chromospheric and photospheric activities on Kepler-411." Monthly Notices of the Royal Astronomical Society 501, no. 2 (November 10, 2020): 1878–90. http://dx.doi.org/10.1093/mnras/staa3793.
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ABSTRACT We present an analysis of the starspot evolution, the surface differential rotation (SDR), the correlation between chromospheric activity indicators and the spatial connection between chromospheric and photospheric activities on the active star Kepler-411, using time-series photometry over four years from Kepler, and spectroscopic data from Keck I 10-m and Lijiang 2.4-m telescopes. We constructed the light curve (LC) by re-performing photometry and reduction from the Target Pixel Files and Cotrending Basis Vectors with a manually redefined aperture using the software pyke3. An efficient program, gemc_lcm, was developed to apply a two-spots model to chosen LC segments with three spot groups at fixed latitudes (30○, 45○), (30○, 60○) and (45○, 60○). We found a periodic variation of the starspots at the period of about 660 d which independs on spot latitudes, and estimated the lower limit of SDR rate α = 0.1016(0.0023) and equatoral rotation period Peq = 9.7810(0.0169) d. Simultaneously, the relative variations of chromospheric activity indicators were derived by subtracting the overall mean spectrum from individual spectrum. It is found that Ca ii H and K emissions are strongly correlated with each other, and there also exists a correlation between Hα and Ca ii H & K emissions, with large dispersion, in accordance with previous results. Furthermore, we find the correlation between Ca ii H and K emissions is different in 2011 and 2012. The chromospheric emission variation shows a highly spatial anticorrelation with the LC, suggesting a spatial connection between the chromospheric active region and spot region.
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Filion, Carrie, and Rosemary F. G. Wyse. "The Far-away Blues: Exploring the Furthest Extents of the Boötes I Ultra-faint Dwarf Galaxy." Astrophysical Journal 923, no. 2 (December 1, 2021): 218. http://dx.doi.org/10.3847/1538-4357/ac2df1.
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Abstract Establishing the spatial extents and the nature of the outer stellar populations of dwarf galaxies is necessary for the determination of their total masses, current dynamical states, and past evolution. We here describe our investigation of the outer stellar content of the Boötes I ultra-faint dwarf galaxy, a satellite of the the Milky Way. We identify candidate member blue horizontal branch and blue straggler stars of Boötes I, both tracers of the underlying ancient stellar population, using a combination of multiband Pan-STARRS photometry and Gaia astrometry. We find a total of twenty-four candidate blue horizontal branch member stars with apparent magnitudes and proper motions consistent with membership of Boötes I, nine of which reside at projected distances beyond the nominal King profile tidal radius derived from earlier fits to photometry. We also identify four blue straggler stars of appropriate apparent magnitude to be at the distance of Boötes I, but all four are too faint to have high-quality astrometry from Gaia. The outer blue horizontal branch stars that we have identified confirm that the spatial distribution of the stellar population of Boötes I is quite extended. The morphology on the sky of these outer envelope candidate member stars is evocative of tidal interactions, a possibility that we explore further with simple dynamical models.
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Gontcharov, George A., and Aleksandr V. Mosenkov. "Gaia DR2 giants in the Galactic dust – II. Application of the reddening maps and models." Monthly Notices of the Royal Astronomical Society 500, no. 2 (September 9, 2020): 2607–19. http://dx.doi.org/10.1093/mnras/staa2728.
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ABSTRACT We exploit a complete sample of 101 810 Gaia DR2 giants, selected in Paper I in the space cylinder with a radius of 700 pc around the Sun and a height of |Z| = 1800 pc, using the Gaia DR2 parallaxes, GBP and GRP photometry, and WISE W3 photometry. We explain the spatial variations of the modes of the observables GBP − GRP and GRP − W3 by the spatial variations of the corresponding reddenings described in the GM20 3D dust distribution model. Presented in this paper, GM20 is an advanced version of the model introduced by Gontcharov in 2009. GM20 proposes two intersecting dust layers, along the Galactic mid-plane and in the Gould Belt, with exponential vertical and sinusoidal longitudinal variations of the dust spatial density in each layer. The Belt layer is an ellipse, oriented nearly between the centre and anticentre of the Galaxy, and with semi-major and semi-minor axes of 600 and 146 pc, respectively. GBP − GRP and GRP − W3 give similar solutions, but different equatorial layer scale heights of 150 ± 15 and 180 ± 15 pc, respectively, and $(G_\mathrm{BP}-G_\mathrm{RP})_0=(1.14\pm 0.01)-(0.022\pm 0.010)\, |Z|$, $(G_\mathrm{RP}-W3)_0=(1.44\pm 0.01)-(0.015\pm 0.010)\, |Z|$, where Z is in kpc. We compare GM20 with several 3D reddening models and maps in their ability to predict the observed colour modes. GM20 and the 3D map by Gontcharov appear to be the best among the models and maps, respectively. However, the most reliable models and maps mainly disagree only in their estimates of low reddening, including the reddening across the whole dust layer.
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Frogel, Jay A., and Edgardo Costa. "Large Magellanic Cloud Carbon Stars: Reading the Rosetta Stone of Stellar Evolution." Symposium - International Astronomical Union 177 (2000): 41–50. http://dx.doi.org/10.1017/s0074180900002230.
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We discuss new results based on RI and JHK photometry for 888 and 204 carbon stars, respectively, of the 1035 C stars found by Blanco and his collaborators in the Large Magellanic Cloud (LMC). Bolometric magnitudes and effective temperatures for these stars are calculated and compared with theoretical predictions. We find a spatial gradient in the transition luminosity between M and C type stars. This has implications for the age of the most recent major epoch of star formation in the LMC.
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Abdurro’uf, Yen-Ting Lin, Hiroyuki Hirashita, Takahiro Morishita, Sandro Tacchella, Masayuki Akiyama, Tsutomu T. Takeuchi, and Po-Feng Wu. "Dissecting Nearby Galaxies with piXedfit. I. Spatially Resolved Properties of Stars, Dust, and Gas as Revealed by Panchromatic SED Fitting." Astrophysical Journal 926, no. 1 (February 1, 2022): 81. http://dx.doi.org/10.3847/1538-4357/ac439a.
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Abstract We study spatially resolved properties (on spatial scales of ∼1–2 kpc out to at least 3 effective radii) of the stars, dust, and gas in 10 nearby spiral galaxies. The properties of the stellar population and dust are derived by fitting the spatially resolved spectral energy distribution (SED) with more than 20 photometric bands ranging from far-ultraviolet to far-infrared. Our newly developed software piXedfit performs point-spread function matching of images, pixel binning, and models the stellar light, dust attenuation, dust emission, and emission from a dusty torus heated by an active galactic nucleus simultaneously through the energy-balance approach. With this self-consistent analysis, we present the spatially resolved version of the IRX–β relation, finding that it is consistent with the relationship from the integrated photometry. We show that the old stellar populations contribute to the dust heating, which causes an overestimation of the star formation rate (SFR) derived from the total ultraviolet and infrared luminosities on kiloparsec scales. With archival high-resolution maps of atomic and molecular gas, we study the radial variation of the properties of the stellar populations (including stellar mass, age, metallicity, and SFR), dust (including dust mass, dust temperature, and abundance of polycyclic aromatic hydrocarbon), and gas, as well as dust-to-stellar mass and dust-to-gas mass ratios. We observe a depletion of the molecular gas mass fraction in the central region of the majority of the galaxies, suggesting that the lack of available fuel is an important factor in suppressing the specific SFR at the center.
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Gadotti, Dimitri A., Adrian Bittner, Jesús Falcón-Barroso, Jairo Méndez-Abreu, Taehyun Kim, Francesca Fragkoudi, Adriana de Lorenzo-Cáceres, et al. "Kinematic signatures of nuclear discs and bar-driven secular evolution in nearby galaxies of the MUSE TIMER project." Astronomy & Astrophysics 643 (October 27, 2020): A14. http://dx.doi.org/10.1051/0004-6361/202038448.
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The central regions of disc galaxies hold clues to the processes that dominate their formation and evolution. To exploit this, the TIMER project has obtained high signal-to-noise and spatial resolution integral-field spectroscopy data of the inner few kpc of 21 nearby massive barred galaxies, which allows studies of the stellar kinematics in their central regions with unprecedented spatial resolution. We confirm theoretical predictions of the effects of bars on stellar kinematics and identify box/peanuts through kinematic signatures in mildly and moderately inclined galaxies, finding a lower limit to the fraction of massive barred galaxies with box/peanuts at ∼62%. Further, we provide kinematic evidence of the connection between barlenses, box/peanuts, and bars. We establish the presence of nuclear discs in 19 galaxies and show that their kinematics are characterised by near-circular orbits with low pressure support and that they are fully consistent with the bar-driven secular evolution picture for their formation. In fact, we show that these nuclear discs have, in the region where they dominate, larger rotational support than the underlying main galaxy disc. In addition, we define a kinematic radius for the nuclear discs and show that it relates to bar radius, ellipticity and strength, and bar-to-total ratio. Comparing our results with photometric studies of galaxy bulges, we find that careful, state-of-the-art galaxy image decompositions are generally able to discern nuclear discs from classical bulges if the images employed have high enough physical spatial resolution. In fact, we show that nuclear discs are typically identified in such image decompositions as photometric bulges with (near-)exponential profiles. However, we find that the presence of composite bulges (galaxies hosting both a classical bulge and a nuclear disc) can often be unnoticed in studies based on photometry alone and suggest a more stringent threshold to the Sérsic index to identify galaxies with pure classical bulges.
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Alfaro, Emilio J., Miguel Cerviño, J. A. Rubiño, Jesus Cabrera-Caño, and José M. Vílchez. "On the spatial distribution of the galactic Wolf-Rayet stars." Symposium - International Astronomical Union 193 (1999): 56–57. http://dx.doi.org/10.1017/s0074180900204920.
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From a new compilation of spectral types and photometry (version April '98 on the Web) performed by van der Hucht for the Galactic WR stars, we have estimated the distance using two different luminosity-spectral type calibrations. Both determinations lead to similar results. On the basis of newly determined distances we have performed a quantitative analysis of the spatial density distribution for the WN and WC spectral types as well as for the whole WR sample and compared them to the one depicted by the large star-forming regions delineated by the population of young open clusters (YOCs). WR stars show a clumpy distribution similar to the one shown by the YOCs and the WN and WC spectral classes present different galactic distributions as well. Otherwise, variations of the WC/WN quotient do not show a clear correlation with the galactic metallicity gradient, on the contrary this ratio seems to be constant on regions of about 1 kpc in size and shows significant variations (even by a factor of 8) between the closest star-forming complexes.
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Wilson, Richard, and Heide Friedrich. "Coupling of Ultrasonic and Photometric Techniques for Synchronous Measurements of Unconfined Turbidity Currents." Water 10, no. 9 (September 14, 2018): 1246. http://dx.doi.org/10.3390/w10091246.
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By synchronizing data collection, such as photometric and ultrasonic Doppler profiling (UVP) measurement techniques, new insights can be obtained into environmental flows, such as highly dynamic turbidity currents. We introduce a combined experimental setup, which ultimately allows a time reduction in testing programmes, and discuss the measurement advances with the help of four surface conditions we tested for unconfined turbidity currents: (a) a smooth surface; (b) a smooth surface with an obstacle present; (c) a rough surface; and (d) a rough surface with an obstacle present. We show that data from both measurement techniques indicate that a rough surface reduces global current velocities and the magnitude of turbidity current phenomena, including Kelvin-Helmholtz instabilities and lobe-and-cleft formation. However, by coupling the techniques, photometric data give valuable insight into the spatial development of instabilities, such as the grouping of lobe and cleft formations. The presence of an obstacle causes local regions of an increased and decreased velocity, but does not affect the global current velocity. Additionally, the obstacle created three local intensity maxima upstream, dissipating to two maxima downstream, supporting the presence of local eddies. The study shows that the combination of UVP and photometry is an effective way forward for obtaining detailed qualitative and quantitative insights into turbulent flow characteristics and we highlight the potential for future research.
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Kawahara, Hajime, and Yuka Fujii. "Image Retrieval of Earth-like Planets from Light Curves." Proceedings of the International Astronomical Union 8, S293 (August 2012): 71–73. http://dx.doi.org/10.1017/s1743921313012568.
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AbstractSurface environment of habitable exoplanets will be important for astrobiologists on exoplanets in near future. Diverse surface environments on the Earth including continents, ocean, and meteorological condition (clouds and rains) serve as the backbone of biodiversity. One of the promising approaches to know the landscape of the terrestrial exoplanets is to use scattered light of the planet through direct imaging.Since spin rotation and orbital revolution change illuminating area on planetary surface and cause time variation to disk-integrated brightness, light curves carry spatial information on the planetary surface. We propose an inversion technique of annual reflected light curves to sketch a two-dimensional albedo map of exoplanets, named the spin-orbit tomography (SOT). Applying the SOT to realistic simulations of the reflected light of an Earth-twin, we demonstrate how the SOT works. The mean cloud and continental distributions can be roughly obtained with single band photometry and difference of two-bands photometry, respectively. The SOT retrieves the planetary image without actually resolving the planet, which can be used to know the habitat of the exoplanets in near future.
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Stonkutė, R., M. Čeponis, A. Leščinskaitė, R. Naujalis, and V. Vansevičius. "Dwarf irregular galaxy Leo A extends even farther, according to HST WFC3 photometry." Astronomy & Astrophysics 614 (June 2018): A144. http://dx.doi.org/10.1051/0004-6361/201731840.
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Context. Leo A is an isolated gas-rich dwarf irregular galaxy of low stellar mass and metallicity residing at the outskirts of the Local Group. Ages of the stellar populations in Leo A range from ~10 Myr to ~10 Gyr. A large stellar halo (up to the deprojected distance of ~1.7 kpc) was discovered based on Subaru wide-field photometry of red giant branch stars. Aims. We aim to study stellar populations at the very outer region of the Leo A galaxy. Methods. We analysed HST WFC3 archive observation data in the field that is partly located beyond the previously known limits of the Leo A galaxy. We performed photometry of star-like objects in the F475W and F814W passbands and studied the spatial distribution of the Leo A stars below the horizontal branch. Results. We report a discovery of stellar halo populations (subgiants and faint red giants) in the Leo A galaxy extending up to ~2.3 kpc deprojected distance from the galaxy centre. Analysis of the colour-magnitude diagram suggests old (>5 Gyr) stellar populations of very low metallicity (Z ~ 0.0001).
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Molino, A., M. V. Costa-Duarte, C. Mendes de Oliveira, A. J. Cenarro, G. B. Lima Neto, E. S. Cypriano, L. Sodré, et al. "J-PLUS: On the identification of new cluster members in the double galaxy cluster A2589 and A2593 using PDFs." Astronomy & Astrophysics 622 (February 2019): A178. http://dx.doi.org/10.1051/0004-6361/201731348.
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Aims. We aim to use multiband imaging from the Phase-3 Verification Data of the J-PLUS survey to derive accurate photometric redshifts (photo-z) and look for potential new members in the surroundings of the nearby galaxy clusters A2589 (z = 0.0414) & A2593 (z = 0.0440), using redshift probability distribution functions (PDFs). The ultimate goal is to demonstrate the usefulness of a 12-band filter system in the study of largescale structure in the local Universe. Methods. We present an optimized pipeline for the estimation of photometric redshifts in clusters of galaxies. This pipeline includes a PSF-corrected photometry, specific photometric apertures capable of enhancing the integrated signal in the bluest filters, a careful recalibration of the photometric uncertainties and accurate upper-limit estimations for faint detections. To foresee the expected precision of our photo-z beyond the spectroscopic sample, we designed a set of simulations in which real cluster galaxies are modeled and reinjected inside the images at different signal-to-noise ratio (S/N) levels, recomputing their photometry and photo-z estimates. Results. We tested our photo-z pipeline with a sample of 296 spectroscopically confirmed cluster members with an averaged magnitude of ⟨r⟩ = 16.6 and redshift ⟨z⟩ = 0.041. The combination of seven narrow and five broadband filters with a typical photometric-depth of r ~ 21.5 provides δz/(1 + z) = 0.01 photo-z estimates. A precision of δz/(1 + z) = 0.005 is obtained for the 177 galaxies brighter than magnitude r < 17. Based on simulations, a δz/(1 + z) = 0.02 and δz/(1 + z) = 0.03 is expected at magnitudes ⟨r⟩ = 18 and ⟨r⟩ = 22, respectively. Complementarily, we used SDSS/DR12 data to derive photo-z estimates for the same galaxy sample. This exercise demonstrates that the wavelength-resolution of the J-PLUS data can double the precision achieved by SDSS data for galaxies with a high S/N. Based on the Bayesian membership analysis carried out in this work, we find as much as 170 new candidates across the entire field (~5 deg2). The spatial distribution of these galaxies may suggest an overlap between the systems with no evidence of a clear filamentary structure connecting the clusters. This result is supported by X-ray Rosat All-Sky Survey observations suggesting that a hypothetical filament may have low density contrast on diffuse warm gas. Conclusions. We prove that the addition of the seven narrow-band filters make the J-PLUS data deeper in terms of photo-z-depth than other surveys of a similar photometric-depth but using only five broadbands. These preliminary results show the potential of J-PLUS data to revisit membership of groups and clusters from nearby galaxies, important for the determination of luminosity and mass functions and environmental studies at the intermediate and low-mass regime.
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McLaughlin, Dean E., Jeff Secker, William E. Harris, and Doug Geisler. "Washington photometry of the globular cluster system around NGC 3311. 2: Spatial structure and mass spectrum." Astronomical Journal 109 (March 1995): 1033. http://dx.doi.org/10.1086/117339.
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