Automated analysis of objective-prism spectra - I. Quasar detection

Hewett, Paul C.; Irwin, M. J.; Bunclark, P.; Bridgeland, M. T.; Kibblewhite, E. J.; He, Xinlei; Smith, M. G.

doi:10.1093/mnras/213.4.971

Cited by 61 publications

(32 citation statements)

References 0 publications

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“…The stability of the TRES instrument allowed us to define the aperture trace for each fiber using the high signal-to-noise flat fields, which were then used to extract the target and calibration spectra, employing the "optimal" (in a least squares sense) weighting scheme of Hewett et al (1985). The spectra were wavelength-calibrated using the standard ecidentify procedure, which employs the (known) dispersion relation of theéchelle to solve for a wavelength solution over all orders of the spectrum simultaneously.…”

Section: Spectroscopymentioning

confidence: 99%

Gj 3236: A New Bright, Very Low Mass Eclipsing Binary System Discovered by the Mearth Observatory

Irwin

Charbonneau

Berta

et al. 2009

ApJ

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We report the detection of eclipses in GJ 3236, a bright (I = 11.6), very low mass binary system with an orbital period of 0.77 days. Analysis of light and radial velocity curves of the system yielded component masses of 0.38 ± 0.02 M and 0.28 ± 0.02 M . The central values for the stellar radii are larger than the theoretical models predict for these masses, in agreement with the results for existing eclipsing binaries, although the present 5% observational uncertainties limit the significance of the larger radii to approximately 1σ . Degeneracies in the light curve models resulting from the unknown configuration of surface spots on the components of GJ 3236 currently dominate the uncertainties in the radii, and could be reduced by obtaining precise, multiband photometry covering the full orbital period. The system appears to be tidally synchronized and shows signs of high activity levels as expected for such a short orbital period, evidenced by strong Hα emission lines in the spectra of both components. These observations probe an important region of mass-radius parameter space around the predicted transition to fully convective stellar interiors, where there are a limited number of precise measurements available in the literature.

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Section: Spectroscopymentioning

confidence: 99%

Gj 3236: A New Bright, Very Low Mass Eclipsing Binary System Discovered by the Mearth Observatory

Irwin

Charbonneau

Berta

et al. 2009

ApJ

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“…( 1 ) Reference Cross-section model Comment Hewett et al (1985) average along dispersion assumes no order tilt Horne (1986), Robertson (1986) polynomials along dispersion assumes small order tilt Urry & Reichert (1988) Gaussian function Marsh (1989) coupled polynomials along dispersion employs spatial subpixel grid Piskunov & Valenti (2002) penalised functions in spatial direction employs spatial subpixel grid This work (master flat) requires stabilised spectrograph where wavelength λ and the positions x and y in the detector plane are continuous variables (the hat indicates the model or best estimate, while without the hat it indicates observations with noise: S (x, y) =Ŝ (x, y) + σ(x, y)). Furthermore, the spectrum is recorded and binned by detector pixels.…”

Section: Principle Of Flat-relative Optimal Extraction (Fox)mentioning

confidence: 99%

“…If there is no or slow order tilt, the profile might be reconstructed by averaging (Hewett et al 1985) or fitting low-order polynomials in the dispersion direction (Horne 1986), respectively. For echelle spectrographs, this situation occurs only in small sections of the orders, but not in general.…”

Section: Conceptual Comparison With Other Optimal Extraction Implemenmentioning

confidence: 99%

Flat-relative optimal extraction

Zechmeister

Anglada-Escudé

Reiners

2013

A&A

133

112

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Context. Optimal extraction is a key step in processing the raw images of spectra as registered by two-dimensional detector arrays to a one-dimensional format. Previously reported algorithms reconstruct models for a mean one-dimensional spatial profile to assist a properly weighted extraction. Aims. We outline a simple optimal extraction algorithm (including error propagation), which is very suitable for stabilised, fibre-fed spectrographs and does not model the spatial profile shape. Methods. A high signal-to-noise ratio, master-flat image serves as reference image and is directly used as an extraction profile mask. Each extracted spectral value is the scaling factor relative to the cross-section of the unnormalised master flat that contains all information about the spatial profile, as well as pixel-to-pixel variations, fringing, and blaze. The extracted spectrum is measured relative to the flat spectrum. Results. Using echelle spectra of the HARPS spectrograph we demonstrate a competitive extraction performance in terms of a signal-to-noise ratio and show that extracted spectra can be used for high precision radial velocity measurement. Conclusions. Pre-or post-flat-fielding of the data is not necessary, since all spectrograph inefficiencies inherent to the extraction mask are automatically accounted for. Also the reconstruction of the mean spatial profile by models is not needed, thereby reducing the number of operations to extract spectra. Flat-relative optimal extraction is a simple, efficient, and robust method that can be applied easily to stabilised, fibre-fed spectrographs.

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“…This provides a coordinate list which is then fed to the APM scanner and the spectra of some 30000 to 60000 objects per plate are then automatically extracted. The extracted spectral data are analysed in order to identify the quasar candidates using techniques similar to those developed at the APM facility by Hewett et al (1985) for the lower redshift objects (z < 3) in the IllaJ surveys. We have developed an algorithm to detect the higher redshift objects (2.5 < z < 4) and other non-UVX quasars based on a median template method.…”

Section: A P M Scanning and Object Selectionmentioning

confidence: 99%

The Red Bright Quasar Survey (RBQS)

Sealey¹,

Drinkwater²,

Irwin³

et al. 1995

International Astronomical Union Colloquium

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Abstract. We are using the UK Schmidt telescope (UKST) to carry out a new objective prism survey, covering 2000-3000 square degrees of high galactic latitude sky in the equatorial region. The survey is targeted at discovering both bright (R < 18) quasars in general and bright high redshift (2 < z < 4) quasars in particular, which will be valuable for high resolution spectroscopic follow-up studies. We are using a mixture of ultra-violet excess (XJVX) and a new template matching technique to identify all the bright quasars. Details of the project are discussed and some preliminary results of the survey are presented.

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Automated analysis of objective-prism spectra - I. Quasar detection

Cited by 61 publications

References 0 publications

Gj 3236: A New Bright, Very Low Mass Eclipsing Binary System Discovered by the Mearth Observatory

Gj 3236: A New Bright, Very Low Mass Eclipsing Binary System Discovered by the Mearth Observatory

Flat-relative optimal extraction

The Red Bright Quasar Survey (RBQS)

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