scholarly journals RASSINE: Interactive tool for normalising stellar spectra

2020 ◽  
Vol 640 ◽  
pp. A42 ◽  
Author(s):  
M. Cretignier ◽  
J. Francfort ◽  
X. Dumusque ◽  
R. Allart ◽  
F. Pepe
Keyword(s):  
Spectral Lines ◽  
Parameter Determination ◽  
Polynomial Fitting ◽  
Stellar Spectra ◽  
Photon Noise ◽  
Graphical Feedback ◽  
Noise Limit ◽  
On Line ◽  
Band Absorption ◽  
Line Depth

Aims. We provide an open-source code allowing an easy, intuitive, and robust normalisation of spectra. Methods. We developed RASSINE, a Python code for normalising merged 1D spectra through the concepts of convex hulls. The code uses six parameters that can be easily fine-tuned. The code also provides a complete user-friendly interactive interface, including graphical feedback, that helps the user to choose the parameters as easily as possible. To facilitate the normalisation even further, RASSINE can provide a first guess for the parameters that are derived directly from the merged 1D spectrum based on previously performed calibrations. Results. For HARPS spectra of the Sun that were obtained with the HELIOS solar telescope, a continuum accuracy of 0.20% on line depth can be reached after normalisation with RASSINE. This is three times better than with the commonly used method of polynomial fitting. For HARPS spectra of α Cen B, a continuum accuracy of 2.0% is reached. This rather poor accuracy is mainly due to molecular band absorption and the high density of spectral lines in the bluest part of the merged 1D spectrum. When wavelengths shorter than 4500 Å are excluded, the continuum accuracy improves by up to 1.2%. The line-depth precision on individual spectrum normalisation is estimated to be ∼0.15%, which can be reduced to the photon-noise limit (0.10%) when a time series of spectra is given as input for RASSINE. Conclusions. With a continuum accuracy higher than the polynomial fitting method and a line-depth precision compatible with photon noise, RASSINE is a tool that can find applications in numerous cases, for example stellar parameter determination, transmission spectroscopy of exoplanet atmospheres, or activity-sensitive line detection.

scholarly journals The effect of surface gravity on line-depth ratios in the wavelength range 0.97–1.32 µm

2020 ◽  
Vol 494 (2) ◽  
pp. 1724-1734
Author(s):  
Mingjie Jian ◽  
Daisuke Taniguchi ◽  
Noriyuki Matsunaga ◽  
Naoto Kobayashi ◽  
Yuji Ikeda ◽  
...  
Keyword(s):  
Spectral Lines ◽  
Surface Gravity ◽  
Line Pair ◽  
On Line ◽  
Optical Wavelengths ◽  
The Difference ◽  
Band Spectra ◽  
Parameter Ranges ◽  
Line Depth ◽  
Effect Of Surface

ABSTRACT A line-depth ratio (LDR) of two spectral lines with different excitation potentials is expected to be correlated with the effective temperature (Teff). It is possible to determine Teff of a star with a precision of tens of Kelvin if dozens or hundreds of tight LDR–Teff relations can be used. Most of the previous studies on the LDR method were limited to optical wavelengths, but Taniguchi and collaborators reported 81 LDR relations in the YJ band, 0.97–1.32 µm, in 2018. However, with their sample of only 10 giants, it was impossible to account for the effects of surface gravity and metallicity on the LDRs well. Here, we investigate the gravity effect based on YJ-band spectra of 63 stars including dwarfs, giants, and supergiants observed with the WINERED spectrograph. We found that some LDR–Teff relations show clear offsets between the sequence of dwarfs and those of giants/supergiants. The difference between the ionization potentials of the elements considered in each line pair and the corresponding difference in the depths can, at least partly, explain the dependency of the LDR on the surface gravity. In order to expand the stellar parameter ranges that the LDR method can cover with high precision, we obtained new sets of LDR–Teff relations for solar-metal G0–K4 dwarfs and F7–K5 supergiants, respectively. The typical precision that can be achieved with our relations is 10–30 K for both dwarfs and supergiants.

scholarly journals Atomic physics and solar polarimetry

2017 ◽  
Vol 95 (9) ◽  
pp. 847-854 ◽  
Author(s):  
P.G. Judge
Keyword(s):  
Adaptive Optics ◽  
Atomic Physics ◽  
Solar Physics ◽  
Polarized Light ◽  
Initial Study ◽  
Spectral Lines ◽  
Calibration Data ◽  
Science Data ◽  
On Line ◽  
Singly Charged

Major outstanding problems in solar physics relate to solar magnetism. Spectropolarimetry offers the best, and sometimes only, method of obtaining accurate measurements of the Sun’s magnetic field. New 1.5–2 m class telescopes with adaptive optics have come on line, and the Daniel K. Inouye 4 m Solar Telescope (DKIST) will begin observing in 2019. The calibration of polarized light entering such a large and polarizing ground-based telescope represents difficult challenges. This paper explores how special polarization properties of particular atomic transitions may provide calibration data, augmenting or even avoiding time-consuming calibration observations, as well as science data. This initial study concludes that solar spectral lines exist with special polarization properties, allowing the telescope calibration to be determined. The Sun’s visible and infrared spectrum is dominated by lines of neutral atoms and singly charged ions of iron and other complex atoms. Both solar and atomic physics should jointly benefit from telescopic advances, as observers explore regimes of broader wavelength ranges, and higher spatial resolutions and polarimetric sensitivities, than they have reached in the past. Further work is in progress to identify particular transitions of practical use to aid in calibrations.

scholarly journals Average Variations of Photospheric FeI and FeII Line Parameters as Function of the Magnetic Filling Factor

1990 ◽  
Vol 138 ◽  
pp. 41-46
Author(s):  
P.N. Brandt ◽  
M. Steinegger
Keyword(s):  
Filling Factor ◽  
Line Strength ◽  
Blue Shift ◽  
Disk Center ◽  
Flux Tubes ◽  
On Line ◽  
Fourier Transform Spectra ◽  
Similar Depth ◽  
Line Depth ◽  
The Continuum

A series of 17 Fourier transform spectra taken at the McMath telescope near disk center in regions of different magnetic field strengths were analyzed. Applying a multi-variate regression analysis magnetic filling factors 0 < α ≥ 0.11 were determined. With α increasing from 0 to 0.11, line bisectors averaged over groups of lines of similar depth are found to show a blue shift decreasing from 0.35 km s–1 to nearly 0.1 km s–1, when referred to the MgI line λ5172.7å. The bisectors of FeII lines exhibit smaller blue shifts than FeI lines. The increase of bisector red shift near the continuum with increasing α, found earlier by Brandt and Solanki (1987), was confirmed and is tentatively interpreted as a manifestation of downdrafts in the vicinity of flux tubes (Deinzer et al., 1984).A significant increase of line width (typically between 3 and 8%, depending on line strength) and a decrease of line depth is found with increasing filling factor. For strong lines the equivalent width W shows no variation or a slight increase, while for the weaker lines a reduction of W between a few % and > 10% is found.

scholarly journals Formation Depths of Spectral Lines in Cepheids

1995 ◽  
Vol 155 ◽  
pp. 373-374
Author(s):  
Michael D. Albrow ◽  
P. L. Cottrell
Keyword(s):  
Spectral Line ◽  
Velocity Fields ◽  
Radial Velocities ◽  
Spectral Lines ◽  
Line Formation ◽  
Ionisation Potential ◽  
Velocity Gradients ◽  
Different Levels ◽  
Line Depth

There has been a number of observational programmes that have endeavoured to investigate the atmospheric velocity fields in Cepheids (e.g., Sanford 1956, Wallerstein et al. 1992, Butler 1993). These studies measured the radial velocities of lines of different strength, excitation and ionisation potential as these provide an indication of line formation at different levels in the atmosphere. From these measurements, the presence of velocity gradients can be inferred, but determination of the magnitude of such gradients requires knowledge of the spectral line depth of formation. Through dynamical modelling we are endeavouring to ascertain what is actually being measured in the above observational programmes.

scholarly journals Laboratory astrophysics for the interpretation of stellar spectra

2019 ◽  
Vol 15 (S350) ◽  
pp. 345-349
Author(s):  
Ulrike Heiter
Keyword(s):  
Milky Way ◽  
Chemical Elements ◽  
Spectral Lines ◽  
Laboratory Astrophysics ◽  
Atomic Data ◽  
Milky Way Galaxy ◽  
Infrared Wavelength ◽  
Stellar Spectra ◽  
Continuous Activities ◽  
Host Stars

AbstractHigh-resolution stellar spectra are important tools for studying the chemical evolution of the Milky Way Galaxy, tracing the origin of chemical elements, and characterizing planetary host stars. Large amounts of data have been accumulating, in particular in the optical and infrared wavelength regions. The observed spectral lines are interpreted using model spectra that are calculated based on transition data for numerous species, in particular neutral and singly ionized atoms. We rely heavily on the continuous activities of laboratory astrophysics groups that produce high-quality experimental and theoretical atomic data for the relevant transitions. We give examples for the precision with which the chemical composition of stars observed by different surveys can be determined, and discuss future needs from laboratory astrophysics.

scholarly journals The potential of many-line inversions of photospheric spectropolarimetric data in the visible and near UV

2019 ◽  
Vol 622 ◽  
pp. A36 ◽  
Author(s):  
T. L. Riethmüller ◽  
S. K. Solanki
Keyword(s):  
Wavelength Range ◽  
Solar Physics ◽  
Solar Observatory ◽  
Spectral Lines ◽  
Resolving Power ◽  
Short Wavelength Range ◽  
Photon Noise ◽  
Infrared Spectral ◽  
The Many

Our knowledge of the lower solar atmosphere is mainly obtained from spectropolarimetric observations, which are often carried out in the red or infrared spectral range and almost always cover only a single or a few spectral lines. Here we compare the quality of Stokes inversions of only a few spectral lines with many-line inversions. In connection with this, we have also investigated the feasibility of spectropolarimetry in the short-wavelength range, 3000 Å−4300 Å, where the line density but also the photon noise are considerably higher than in the red, so that many-line inversions could be particularly attractive in that wavelength range. This is also timely because this wavelength range will be the focus of a new spectropolarimeter in the third science flight of the balloon-borne solar observatory SUNRISE. For an ensemble of state-of-the-art magneto-hydrodynamical atmospheres we synthesize exemplarily spectral regions around 3140 Å (containing 371 identified spectral lines), around 4080 Å (328 lines), and around 6302 Å (110 lines). The spectral coverage is chosen such that at a spectral resolving power of 150 000 the spectra can be recorded by a 2K × 2K detector. The synthetic Stokes profiles are degraded with a typical photon noise and afterward inverted. The atmospheric parameters of the inversion of noisy profiles are compared with the inversion of noise-free spectra. We find that significantly more information can be obtained from many-line inversions than from a traditionally used inversion of only a few spectral lines. We further find that information on the upper photosphere can be significantly more reliably obtained at short wavelengths. In the mid and lower photosphere, the many-line approach at 4080 Å provides equally good results as the many-line approach at 6302 Å for the magnetic field strength and the line-of-sight (LOS) velocity, while the temperature determination is even more precise by a factor of three. We conclude from our results that many-line spectropolarimetry should be the preferred option in the future, and in particular at short wavelengths it offers a high potential in solar physics.

29b. Working Group on Line Intensity Standards

1970 ◽  
Vol 14 (1) ◽  
pp. 331-331
Author(s):  
G. Cayrel De Strobel
Keyword(s):  
Equivalent Width ◽  
Working Group ◽  
General Assembly ◽  
High Dispersion ◽  
Minor Planets ◽  
Double Pass ◽  
Stellar Spectra ◽  
Primary Object ◽  
On Line ◽  
True Values

Systematic equivalent width comparisons as initiated by K. O. Wright during the Seventh General Assembly of the IAU in 1948 and continued by G. Cayrel de Strobel since the Twelfth General Assembly in 1964 are meeting less and less response from the astronomical community. Griffin has stressed systematic errors in spectrographic results. For instance he claims in his paper (M.N.R.A.S., 143, 319) that owing to the light thrown in the wings of the instrumental profiles, the observed equivalent widths of absorption lines in late type stellar spectra are 5 to 10 % less than the true values. Furthermore Griffin pointed out the weakness of purely spectrographic comparisons which are all affected by the same type of errors. What is really needed is to know the true equivalent width of a few lines as they can be obtained from an accurate double pass photoelectric scanner. Pagel suggested that this can be done by comparing spectra of integrated sunlight from sky or minor planets with scans obtained by solar spectrometers. Griffin prefers that a bright star be used for this purpose. A complete change in the activity of this working group could very well be decided if the primary object is to have true standards of equivalent widths and if these cannot be obtained from conventional high dispersion spectrography.

scholarly journals Numerical Simulation of Granular Convection: Effects on Photospheric Spectral Line Profiles

1980 ◽  
Vol 51 ◽  
pp. 213-224
Author(s):  
Åke Nordlund
Keyword(s):  
Spectral Line ◽  
Line Strength ◽  
Blue Shift ◽  
Spectral Lines ◽  
Line Profiles ◽  
Pressure Broadening ◽  
Solar Granulation ◽  
Velocity Fluctuations ◽  
Excitation Potential ◽  
On Line

AbstractThe results of numerical simulations of the solar granulation are used to investigate the effects on photospheric apectral lines of the correlated velocity and temperature fluctuations of the convective granular motions. It is verified that the granular velocity field is the main cause for the observed broadening and strengthening of photospheric spectral lines relative to values expected from pure thermal and pressure broadening. These effects are normally referred to as being due to “macro-turbulence” and “micro-turbulence”, respectively. It is also shown that the correlated temperature and velocity fluctuations produce a “convective blue shift” in agreement with the observed blue shift of photospheric spectral lines. Reasons are given for the characteristic shapes of spectral line bisectors, and the dependence of these shapes on line strength, excitation potential, and center to limb distance are discussed.

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