scholarly journals A New Method of Wavelength Calibration for LAMOST by Combining Short- and Long-Exposure Spectral Lines

2012 ◽  
Vol 29 (1) ◽  
pp. 66-71 ◽  
Author(s):  
G. H. Ye ◽  
J. Zhu ◽  
Z. F. Ye
Keyword(s):  
Spectral Lines ◽  
New Method ◽  
Short Exposure ◽  
Selected Lines ◽  
Wavelength Calibration ◽  
Calibration Methods

AbstractIn wavelength calibration using arc lines, the normal approach is to use the strongest unsaturated lines, leaving weak lines unused. A new method is proposed in this paper, which not only utilizes the strong spectral lines, but also makes most use of weak spectral lines. In order to validate the effectiveness of the method we propose, experiments are performed on simulated spectra. Firstly, two kinds of spectra are generated: one with a short exposure and another with a long exposure. Secondly, calibration lines are chosen from the short exposure and long exposure spectra separately according to some rules. Thirdly, the initial wavelength calibration is completed by using the selected short-exposure lines. Fourthly, the approximate centroids of the selected long-exposure lines are obtained by utilizing the result of the initial wavelength calibration. These are then adjusted iteratively to obtain the centroids. Finally, the selected lines from the short- and long-exposures are combined to obtain the final wavelength calibration. Compared with traditional calibration methods which only use short exposures and strong lines, the proposed method is shown to be more accurate.

Wavelength Calibration Methods for Low-Resolution Photodiode Array Spectrometers

1993 ◽  
Vol 47 (7) ◽  
pp. 1007-1014 ◽  
Author(s):  
J. Thomas Brownrigg
Keyword(s):  
Measurement Errors ◽  
Calibration Method ◽  
Spectral Lines ◽  
Low Resolution ◽  
Position Measurement ◽  
Wavelength Calibration ◽  
Regression Methods ◽  
Calibration Methods ◽  
Wavelength Pair ◽  
Pair Method

A wavelength calibration method for low-resolution diode array spectrometers is described. The method was developed for routine calibration of 0.1-meter-focal-distance spectrometers having 35- or 38-element silicon diode arrays, normally operated in the 340–700 nm spectral range. Each diode of the array is approximately 1 mm wide, giving an instrumental bandwidth of ∼10 nm per diode. The calibration method requires two well-separated monochromatic spectral lines, their central image locations on the array, and the grating groove frequency. This method is compared with nonlinear regression (least-squares) methods, with multiple calibration lines fitted to quadratic or cubic polynomials. The predictive accuracy of the wavelength-pair method compares favorably with the regression methods. A calibration accuracy of ∼±1 nm is expected for the instruments considered here. The method described could, in principle, be applied to instruments with higher resolution, such as those having self-scanned photodiode arrays with 25-μm or 50-μm-wide pixels. For such instruments, however, a large number of calibration lines should be resolved. In this case, the regression method, which averages diode position measurement errors, is probably more accurate. The wavelength-pair method is most useful for low-resolution instruments, for which regression methods may not be practical.

scholarly journals Stellar magnetic imaging from spectropolarimetric data

1996 ◽  
Vol 176 ◽  
pp. 53-60 ◽  
Author(s):  
J.-F. Donati
Keyword(s):  
Small Amplitude ◽  
High Accuracy ◽  
Spectral Lines ◽  
New Method ◽  
Doppler Imaging ◽  
Magnetic Imaging ◽  
Active Stars ◽  
Surface Fields ◽  
Very High

In this paper, I will review the capabilities of magnetic imaging (also called Zeeman-Doppler imaging) to reconstruct spot distributions of surface fields from sets of rotationnally modulated Zeeman signatures in circularly polarised spectral lines. I will then outline a new method to measure small amplitude magnetic signals (typically 0.1% for cool active stars) with very high accuracy. Finally, I will present and comment new magnetic images reconstructed from data collected in 1993 December at the Anglo-Australian Telescope (AAT).

A New Calibration Method and Device for Certified Flow Measurements With Laser Velocimetry

2012 ◽  
Author(s):  
Katsuaki Shirai ◽  
Lars Büttner ◽  
Jürgen Czarske ◽  
Carsten Kykal
Keyword(s):  
Positional Information ◽  
Calibration Method ◽  
Calibration Procedure ◽  
Uncertainty Budget ◽  
New Method ◽  
Direct Access ◽  
Flow Measurements ◽  
Laser Velocimetry ◽  
Traceability Chain ◽  
Calibration Methods

We aim to establish traceability at calibration and hence to enable a certified flow measurement with a calibrated measurement system. A new calibration method is presented for laser velocimetry. We develop a simple, unique method which establishes traceability of its uncertainty. The device is transportable and calibratable by any users for their own instruments on-site. Our new method requires only a rotating disk and a precision linear stage providing positional information. In former calibration methods, the uncertainty of the orbit radius of a scattering object was dominant due to the difficulty of accessing the true center of the rotation. The diffuculty was solved in our new method. The new method provides an accurate estimate of the orbit radius and hence the velocity of the calibration object through a linear regression. The calibration constant is obtained even without the need of direct access to the absolute value of the rotation radius. The uncertainty budget is examined throughout the calibration procedure. The traceability chain is established once the traceabilities are maintained to the translation stage and the motor used for rotating the calibration disk. The new method has been realized with three different calibration setups and their performances were investigated. We demonstrate that the new calibration method can achieve uncertainty down to 0.1%.

scholarly journals A statistical method for the identification of stars enriched in neutron-capture elements from medium-resolution spectra

2019 ◽  
Vol 631 ◽  
pp. A93
Author(s):  
G. Navó ◽  
J. L. Tous ◽  
J. M. Solanes
Keyword(s):  
Statistical Method ◽  
Galaxy Clusters ◽  
Globular Cluster ◽  
Neutron Capture ◽  
Spectral Lines ◽  
Selected Lines ◽  
Spectroscopic Observations ◽  
Large Numbers ◽  
Medium Resolution ◽  
Show Evidence

We present an automated statistical method that uses medium-resolution spectroscopic observations of a set of stars to select those that show evidence of possessing significant amounts of neutron-capture elements. Our tool was tested against a sample of ∼70 000 F- and G-type stars distributed among 215 plates from the Galactic Understanding and Exploration (SEGUE) survey, including 13 that were directed at stellar Galaxy clusters. Focusing on five spectral lines of europium in the visible window, our procedure ranked the stars by their likelihood of having enhanced content of this atomic species and identifies the objects that exhibit signs of being rich in neutron-capture elements as those scoring in the upper 2.5%. We find that several of the cluster plates contain relatively large numbers of stars with significant absorption around at least three of the five selected lines. The most prominent is the globular cluster M 3, where we measured a fraction of stars that are potentially rich in heavy nuclides, representing at least 15%.

The McDonald Observatory High Precision Radial Velocity Spectrometer

1984 ◽  
Vol 88 ◽  
pp. 109-120
Author(s):  
William D. Cochran ◽  
Brenda W. Young
Keyword(s):  
Radial Velocity ◽  
Large Mass ◽  
Spectral Lines ◽  
Stellar Spectrum ◽  
Stellar Oscillations ◽  
Doppler Shifts ◽  
Calibration Methods ◽  
Fabry Perot ◽  
Fixed Reference ◽  
Low Amplitude

AbstractWe are developing a prototype instrument for McDonald Observatory designed to measure stellar radial velocity variations to a precision of a few meters per second. The instrument will be used to study low amplitude stellar oscillations, to search for binary stellar systems with large mass ratios, and possibly to search for extra-solar planetary systems. A fixed gap Fabry-Perot etalon, used in reflection, imposes a set of fixed reference absorption lines on the stellar spectrum before it enters the McDonald Observatory 2.7m coudé spectrograph. The spectrum, covering 1500 Å at 0.13 Å resolution, is recorded on a set of eight Reticon arrays, placed end-to-end. Doppler shifts of the stellar spectral lines with respect to the fixed Fabry-Perot orders are measured by cross-correlation techniques. Calibration methods have been developed to measure any long-term drifts within the system.

Accurate Wavelength Calibration of an Etalon-Tuned Dye Laser

1981 ◽  
Vol 35 (6) ◽  
pp. 593-598 ◽  
Author(s):  
G. J. Beenen ◽  
J. W. Hosch ◽  
E. H. Piepmeier
Keyword(s):  
Hollow Cathode ◽  
Dye Laser ◽  
Spectral Lines ◽  
Lasing Wavelength ◽  
Wavelength Calibration ◽  
Birefringent Filter ◽  
Tunable Dye Laser ◽  
Intracavity Etalon ◽  
Better Than

A method to set accurately an etalon-tuned dye laser to any preselected wavelength within its lasing region is presented. The method involves a unique procedure to determine accurately the etalon thickness, so that the correct etalon order can be found for each wavelength and corresponding etalon setting. An equation relating the dial reading on the optical mount of the intracavity etalon to lasing wavelength is derived and evaluated for the Chromatix CMX-4 pulsed tunable dye laser. The procedure used to evaluate the equation parameters is described in detail. After establishing the value of all the equation parameters, a comparison is made between lasing wavelengths as predicted by the equation and as experimentally determined using laser-induced impedance changes to detect spectral lines in hollow cathode lamps. Agreement is found to be better than ±0.05 Å for all spectral lines used, with 68% of the predicted wavelengths within ±0.02 Å of their actual values. The micrometer drive for the birefringent filter, used in the CMX-4 to select an etalon order, is also calibrated using a quadratic polynominal equation, which gives predictions better than ±0.25 Å for all wavelengths tried in the regions of 5890 Å to 6050 Å and 6350 Å to 6720 Å, corresponding to the dyes R6G and R640, respectively.

The Stokes' Shift in Impurity Spectral Lines. I. Mathematical Technique

1972 ◽  
Vol 50 (3) ◽  
pp. 222-230 ◽  
Author(s):  
Robert Barrie ◽  
I. W. Sharpe
Keyword(s):  
Adiabatic Approximation ◽  
Stokes Shift ◽  
Spectral Lines ◽  
New Method ◽  
Mathematical Technique ◽  
Impurity Site ◽  
Systematic Fashion

A new method of deriving the Stokes' shift in impurity spectral lines is presented. The adiabatic approximation is not used. The method makes use of the fact that at most one electron can be bound at the impurity site and reduces the problem in a systematic fashion to the evaluation of traces over only phonon states. A new method is given of evaluating these traces for a particular electron–phonon system which has the chief features required to discuss the Stokes' shift.

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