Synthetic Photometry Research Articles

Spectrophotometry of Flux Calibration Stars for Hubble Space Telescope

view Abstract Citations (30) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrophotometry of Flux Calibration Stars for Hubble Space Telescope Stone, Remington P. S. Abstract Fluxes are presented for 103 stars which were observed for Hubble Space Telescope (HST) calibration. Perhaps the most important aspect of this work is confirmation of a revised zero point for optical flux calibration of HST as described by Colina and Bohlin from synthetic photometry. Two cautions are offered for users of the Oke and Gunn spectrophotometric system, and simple corrections are suggested. The present stars are of interest because of their accessibility and their importance in a variety of standard systems. Included are UV and optical spectrophotometric flux standards, UBVRI and IR photometric standards, and many stars from the Equatorial Selected Areas for which UBVRI colors exist as well. It is hoped that the present data will be of use to those relating results between systems. The spectra generally cover the range λλ4040-8800, with a nominal resolution of about 5.5 Å pixel-1. The data are referred to the absolute calibration of α Lyrae recommended by Mégessier. Tabular magnitude values for Hayes and Oke-Guim wavelengths are presented. The same tables as well as mean magnitudes within 25 Å bins every 25 Å in ASCII and PostScript format, and flux-calibrated spectra, may be obtained from the author. Publication: The Astrophysical Journal Supplement Series Pub Date: November 1996 DOI: 10.1086/192369 Bibcode: 1996ApJS..107..423S Keywords: TECHNIQUES: PHOTOMETRIC full text sources ADS | data products SIMBAD (106)

Photometric Signatures of Starbursts in Interacting Galaxies and the Butcher-Oemler Effect

view Abstract Citations (27) References (52) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometric Signatures of Starbursts in Interacting Galaxies and the Butcher-Oemler Effect Rakos, Karl D. ; Maindl, Thomas I. ; Schombert, James M. Abstract This paper presents new and synthetic narrowband photometry of ellipticals, spirals, Seyferts, and interacting galaxies in an attempt to identify the cause of the unusually high fraction of blue cluster galaxies in distance clusters (Butcher-Oemler effect). The properties and distribution of the low-redshift sample specifically points to starbursts as the origin of the blue narrowband colors in interacting Arp galaxies. Comparison between theoretical models and multicolor diagrams, particularly 4000 A break colors, indicates a photometric signature that differs from both normal disk galaxy star formation and nonthermal components. This photometric signature is absent for the Butcher-Oemler galaxies whose general color distribution, compared to present-day clusters, is consistent with a majority of the blue population involved in normal star formation rates (spiral-like) with the addition of a small fraction of bright, blue interacting/merger systems. This photometric picture of the Butcher-Oemler galaxies is in agreement with the morphological evidence from Hubble Space Telescope imaging. Publication: The Astrophysical Journal Pub Date: July 1996 DOI: 10.1086/177497 arXiv: arXiv:astro-ph/9603047 Bibcode: 1996ApJ...466..122R Keywords: GALAXIES: EVOLUTION; PHOTOMETRY; GALAXIES: STARBURST; Astrophysics E-Print: 24 pages, LaTeX/AAS macros, contact author for tables, accepted for ApJ full text sources arXiv | ADS | data products SIMBAD (22) NED (22)

Properties and calibrations of the Washington photometric system from synthetic photometry

Properties and calibrations of the Washington photometric system from synthetic photometry

The method of synthetic photometry

The method of synthetic photometry

"New" B and V Photometry of the "Old" Type IA Supernova SN 1937C: Implications for HO

view Abstract Citations (33) References (60) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS "New" B and V Photometry of the "Old" Type IA Supernova SN 1937C: Implications for HO Pierce, Michael J. ; Jacoby, George H. Abstract We have digitized and analyzed the original Baade and Zwicky 18 in. Palomar Schmidt films of the type Ia supernova SN 1937C. The data set consists of 76 films in the photographic bandpass mpg and a series of 50 previously unreduced photovisual (m_pv_) films. These data were supplemented by the three known, prediscovery plates of SN 1937C taken by Leutenegger and Grenat. The films and plates were scanned using the KPNO PDS microdensitometer and calibrated by fitting the integrated photographic density to a magnitude sequence of local standards on each film/plate. The resulting calibrations have typical rms dispersions of 0.06 and 0.04 mag for m_pg_ and m_pv_, respectively. Our magnitudes at the earliest epochs are systematically 0.30 mag fainter than those reported by Baade & Zwicky, with the two datasets converging by the eighth observation, about 11 days after maximum. We converted our mpg and mpv photometry to B and V using transformations determined both theoretically using synthetic photometry of spectrophotometric standards, and empirically using the local standard stars. The B and V light curves and B - V color evolution of SN 1937C were fitted with template light curves from previously well-observed supernovae to obtain B_max_= 8.94+/- 0.03, V_max_ = 9.00+/-0.03, and (B - V)_B(max)_ = -0.08 +/- 0.04. These correspond to M(B_max_)= - 19.42 and M( V_max_)= - 19.36 when combined with the Cepheid distance to IC 4182, the host galaxy. In comparing our results with the visual photometry of Beyer we found evidence for a color term which when applied to Beyer's data, leads to V_max_ = 8.87. We stress the importance of determining accurate color terms in the photometry of SN Ia due to the wide color range (from B - V ~ 0 to B - V ~1) through which they evolve over the first 30 days after maximum. The SN 1937C light curves were best fit by templates with very slow rates of decline. The correlation between decline rate and luminosity implies that SN 1937C, with {DELTA}m_15_ = 0.85 mag, was as much as 0.44 mag more luminous than average SN Ia and that it was one of the most intrinsically luminous SN Ia studied to date. The luminosity calibration for SN 1937C was applied to the Hubble relation derived by Hamuy et al. for which distant SNe magnitudes were corrected for their decline rates. This calibration of the SN Ia distance scale yields a Hubble Constant between H_0_ = 68+/-5 km s^-1^ Mpc^-1^ and H_0_ = 74+/-6 km s^-1^ Mpc^-1^, depending on the choice of slope for the decline rate relation. Publication: The Astronomical Journal Pub Date: December 1995 DOI: 10.1086/117737 Bibcode: 1995AJ....110.2885P Keywords: SUPERNOVAE: INDIVIDUAL: SN 1937C; ISM: ABUNDANCES full text sources ADS | data products SIMBAD (8) NED (2)

THE PHOTOMETRIC PERFORMANCE AND CALIBRATION OF WFPC2

ABSTRACT We discuss the photometric performance and calibration of the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telesopce (HST). The stability and accuracy of WFPC2 photometric measurements is discussed, with particular attention given to charge transfer efficiency (CTE) effects, contamination effects in the ultraviolet (UV), and flat field accuracy and normalization. Observational data are presented from both WFPC2 observations and ground observations using a system similar to that flown. WFPC2 photometric systems are defined both for the ground and flight systems. Transformations between these systems and the Landolt UBVRI system are presented. These transformations are sensitive to details in the spectra being transformed, and these sensitivities are quantified and discussed. On-orbit observations are used to revise the prelaunch estimates of response curves to best match synthetic photometry results with observations, and the accuracy of the resulting synthetic photometry is discussed. Synthetic photometry is used to determine zeropoints and transformations for all of the fight filters, and also to derive interstellar extinction values for the WFPC2 system. Using stellar interior and atmosphere models, isochrones in the WFPC2 system are calculated and compared with several observations.

Colours and Teff of Main Sequence Stars Covering the Galactic Metallicity Range

We present the results of a general programme aimed to study the effects of metallicity on the temperature scale of late main sequence stars (F0-K5). A sample of approximately 400 stars with published UBV(RI) and ubvy – β photometry has been collected from the literature. A three years campaign of observations (Alonso et al. 1994b) was carried out to obtain JHK photometry in order to apply the InfraRed Flux Method (IRFM) to derive effective temperatures. The effect of metallicity on Colour-Colour IR diagrams is discussed. The absolute flux calibration in the IR was revised in Alonso et al. (1994a). The effect of metallicity on the bolometric correction has been studied in Alonso et al. (1995) in order to derive bolometric fluxes. The temperatures have been derived by applying the IRFM using new Kurucz models. Teff = f(Colours, [Fe/H], log(g)) relations are obtained for dwarfs covering the ranges 4000K ≤ Teff ≤ 8000K, 3.5 ≤ logg ≤ 5.00, +0.5 ≤ [Fe/H] ≤ −3.00 which expands considerably the database of previous works. These relations are used to check atmosphere models through the analysis of UBV RIJH Kubvy – β synthetic photometry in combination with the IRFM. The transformation from the theoretical HR diagram into an observational one is analyzed with the new relations. The influence of these points on the study of the evolution of the Galaxy is briefly discussed.

JHK Photometry of Extragalactic Sources Using an Infrared Array Camera

The UCLA two-channel IR camera has been used to perform crowded-field photometry in two distinct classes of extragalactic objects. DAOPHOT was used to reduce images of M 33 and provide JHK color-magnitude diagrams of over 1,700 stars. Galaxy photometry in crowded clusters, e.g. Abell 370, was obtained in JHK and analyzed using FOCAS. In both cases, extensive reductions were performed using synthetic aperture photometry for comparison. Methods and results are summarized.

Absolute flux calibration of optical spectrophotometric standard stars

A method based on Landolt photometry in B and V is developed to correct for a wavelength independent offset of the absolute flux level of optical spectrophotometric standards. The method is based on synthetic photometry techniques in B and V and is accurate to approximately 1%. The correction method is verified by Hubble Space Telescope Faint Object Spectrograph absolute fluxes for five calibration stars, which agree with Landolt photometry to 0.5% in B and V.

Exploring the properties of stellar CO bands using synthetic photometry and spectroscopy

A grid of models for cool dwarf and giant stars has been used to calculate synthetic spectra in the region of the 2.3-micron CO bands. These synthetic spectra have been compared with observed spectra for four stars with known abundances, effective temperatures, and surface gravities. The carbon abundances and carbon isotope ratios found from this comparison agree well with those found from high dispersion spectroscopy. The synthetic spectra have been used to calculate tables of CO indices on two different systems. The observed dependence of CO band strength on luminosity is seen in these synthetic indices. These CO indices have also been used to derive carbon abundances for fifteen field giant stars with known atmospheric parameters. The resulting carbon abundances are again in good agreement with those found from high dispersion spectroscopy. Sample CO spectra are presented for globular cluster giant branches. Calculations of CO colors for different oxygen abundances and with carbon abundances which fit the observed G bands suggest that the oxygen abundance is not enhanced in the red giant stars in the very metal-poor cluster NGC 6397. 52 refs.

Photometric calibration of the HST wide-field/planetary camera. I - Ground-based observations of standard stars

This paper describes the observation and analysis of field stars, undertaken as a step toward understanding the photometric properties of the filters and CCDs aboard the Wide-Field/Planetary Camera of the Hubble Space Telescope. Ground-based CCD observations have been made simulating 15 of the most important WF/PC passbands. Data are presented here for an equatorial network of stars including many UBVRI standards and some spectrophotometric standards. They serve to establish a photometric system that will be used in the calibration of in-flight data and that is useful for the calibration of other ground-based data. Transformations between WF/PC and other photometric systems are discussed, as well as the effects of interstellar absorption and atmospheric extinction on data in the WF/PC system. Synthetic photometry has been used as an aid in the data analysis and is described.

The galaxy activity-interaction connection. I - Optical observations

As part of an investigation into the triggering of nuclear radio emission in interacting galaxies, new multicolor, broadband data are presented from a subset of Arp-Madore Catalog galaxies selected on the basis of their optical morphology - systems with loops and/or tails. The CTIO 4 m is used to obtain images in B, V, R, and I for the purpose of performing synthetic aperture photometry. Isophotal ellipse fitting to the more regular objects in the sample is also performed to quantify their isophotal deviation from purely elliptical morphologies. Color index maps for the galaxies are constructed, and the optical morphologies, broadband colors, and detailed photometric properties as well as the IRAS fluxes for the galaxies are discussed. These data are used to obtain a rough measure of the level of activity present in these systems.

Synthetische UBVR‐Photometrien aus flußkalibrierten Spektren

AbstractSince the photometric UBVRI broadband systems of Johnson and Morgan (1951, 1953), Johnson (1955, 1965) and Cousins (1976) were partly illdefined and have partly been modified over the years, their technical realization at different observatories is problematical. Large differences occur especially in measuring objects with peculiar spectra or strong lines. Therefore, firstly an accurate reconstruction of the UBVRI systems of Johnson and the Cousins systems used at the South African Astronomical Observatory (SAAO), at Cerro Tololo Inter‐American Observatory (CTIO) and at Mount Stromlo/Siding Springs Observatory (MSSO) was attempted. The transmissions of the different bands, as well as the possible technical realizations are listed. The data of the Johnson system and the Cousins systems used at SAAO and MSSO were compiled from several publications and new measured transmission curves of the CTIO systems are given. The characteristic wavelengths λ0 have been calculated for all systems. Using flux‐calibrated spectra of 75 early and late type stars in the wavelength range 3200‐8800 Å with a resolution of 10 Å, synthetic photometries of the four described systems and that of Bessell (1990) were derived. The transformation relations from the various systems to the original Johnson system are given in and have been compared to the defined relations. The accuracy of the synthetic photometry is ±0.02 mag in V and (B‐V), ±0.09 mag in (U‐B), and ±0.05 mag in (V‐R). The larger error in (U‐B) is due to the shortwave uncertainties of the U filter transmissions and the missing spectral information because of UV cut‐off of the spectra at λmin > 3200 Å. The uncertainties in (V‐R) are due to the different R filters in the various systems. No synthetic photometry was possible to derive for the I band, because of missing spectral information at λ > 8800 Å.

UBVRI PASSBANDS.

ABSTRACT Good representations of the passbands for the Johnson-Cousins UBVRI system have been devised by comparing synthetic photometry with actual observations and with standard system magnitudes. Small adjustments have been made to previously published passbands. Users are urged to match these passbands so that better photometry and calibration are ensured. Mismatched B bands are shown to be a major source of recent (U - B) transformation problems. The nature of systematic differences between the natural colors of the most widely used sets of standard star photometry is investigated and suggested CCD filter combinations are discussed.

THE DESIGN AND TESTING OF FILTER-DETECTOR SYSTEMS USING SYNTHETIC PHOTOMETRY

ABSTRACT Synthetic photometry is applied to the problem of designing a filter set that, when combined with a CCD, provides photometry that can be transferred to the Johnson (1955) UBV and the Kron-Cousins (1976) VRI systems. A filter set with transformation coefficients less than 0.07 is developed. The color and magnitude residuals from the synthetic photometry show that the transformations are linear over the color ranges, (B-V) between 0.0 and 1.4, (V-R) between 0.0 and 1.0, and (R-I) between 0.0 and 0.8.

The properties of OB supergiants in the Large Magellanic Cloud. II - Spectral types and intrinsic colors

view Abstract Citations (68) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Properties of OB Supergiants in the Large Magellanic Cloud. II. Spectral Types and Intrinsic Colors Fitzpatrick, Edward L. Abstract We have isolated a sample of about 90 of the most lightly reddened "normal" O and B supergiants in the LMC for a study of their spectroscopic and photometric properties. New MK spectral classifications are presented for 83 of the stars, about half of which have no previously reported slit spectral types. Intrinsic color relations are derived for the LMC supergiants using new observations in the Stromgren uvby system and published data in the Johnson UBV system. The shapes of the intrinsic UBV and uvby relations for the LMC stars are similar to published Galactic calibrations for Ia supergiants. In the Stromgren system, the derived spectral type versus intrinsic color calibration for the B supergiants also agrees well with Galactic calibrations. In the Johnson system, the LMC calibration is systematically redder, particularly in (U-B)0, than reported for Galactic stars. Because the LMC calibrations in the two systems have been derived in a mutally consistent manner using the same sample of stars, this suggests that the Galactic calibrations are not consistent. In other words, the Stromgren and Johnson colors attributed to a given Galactic B supergiant subtype cannot be produced by the same star. This inconsistency probably results from the small numbers and the different samples of Galactic supergiants being used in the various calibration studies and from uncertainties introduced by the typically much higher reddening of the Galactic stars. Comparison of the LMC intrinsic color calibrations with synthetic photometry of line-blanketed, plane-parallel, LTE model atmospheres shows that the B-type supergiant colors can be reproduced by this class of models. Publication: The Astrophysical Journal Pub Date: December 1988 DOI: 10.1086/166960 Bibcode: 1988ApJ...335..703F Keywords: Astronomical Photometry; Early Stars; Interstellar Matter; Magellanic Clouds; Supergiant Stars; Ubv Spectra; B Stars; Milky Way Galaxy; O Stars; Astrophysics; GALAXIES: MAGELLANIC CLOUDS; INTERSTELLAR: MATTER; PHOTOMETRY; STARS: EARLY-TYPE; STARS: SPECTRAL CLASSIFICATION; STARS: SUPERGIANTS full text sources ADS | data products SIMBAD (114) GCPD (1) Related Materials (1) Part 1: 1987ApJ...312..596F

Synthetic Stromgren photometry for F dwarf stars

Recent synthetic spectrum and color calculations for cool dwarf star models are tested by comparison with observation. The accuracy of the computed dependence of the thermal colors B-V and b-y on effective temperature is examined, and H-beta indices are presented and compared with observed values. The accuracy of the predictions of the Stromgren uvby system metal-abundance indicator m1 and luminosity indicator c1 are tested. A new calibration of the c1, b-y diagram in terms of absolute magnitudes is given, making use of recent calculations of stellar isochrones. Observations of very metal-poor subdwarfs are used to study the accuracy of the isochrones. The c1, b-y diagram of the subdwarfs is compared with that of the turnoff-region stars in the very metal-poor globular cluster NGC 6397.

Line-Blanketing in Theoretical Model Atmospheres for F, G, and K-Type Stars

We have computed improved flux distributions from Gustafsson et al.'s extensive grids of theoretical model atmospheres for late-type (F-K) giant and dwarf stars. In order to enhance the realism of the computed fluxes throughout the optical and the ultraviolet wavelength ranges, the massive list of atomic opacity sources used for the hotter Kurucz models was also employed in calculating the cooler spectra. For both the giant and the dwarf models, the resulting synthetic UBVRI photometry provides excellent matches to the spectroscopic calibrations of the observed metallicity and temperature scales based on the ultraviolet excesses, δ (U-B), and the BVRI colors, respectively. We conclude that atomic line-blanketing due to known, rather than “missing”, opacity sources accounts for the largest fraction of the systematic UV discrepancy existing between observations and earlier model calculations.

DAOPHOT: A COMPUTER PROGRAM FOR CROWDED-FIELD STELLAR PHOTOMETRY

ABSTRACT The tasks of the DAOPHOT program, developed to exploit the capability of photometrically linear image detectors to perform stellar photometry in crowded fields, are discussed. Raw CCD images are prepared prior to analysis, and following the obtaining of an initial star list with the FIND program, synthetic aperture photometry is performed on the detected objects with the PHOT routine. A local sky brightness and a magnitude are computed for each star in each of the specified stellar apertures, and for crowded fields, the empirical point-spread function must then be obtained for each data frame. The GROUP routine divides the star list for a given frame into optimum subgroups, and then the NSTAR routine is used to obtain photometry for all the stars in the frame by means of least- squares profile fits. The process is illustrated with images of stars in a crowded field, and shortcomings and possible improvements of the program are considered.

Synthetic filter photometry and evolutionary status of two Be stars in the association Per OB1

Stromgren and H-beta colors have been determined from spectrophotometric observations for two Be stars without published photometry in the association Per OB1: HD 12856 (B0 pe) and HD 13890 (B1 III:pe). Stellar parameters and improved spectral types are then derived from the color indices using the calibrations of Jakobsen (1986), and independently from the BCD classification method. The intrinsic properties of HD 12856 and HD 13890 are compared with those of normal B stars and are used to estimate their evolutionary status.