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The disentangled spectrum of telluric lines from the KOREL solution applied to α Boo spectra is compared to two observed Reticon spectra of α Boo, having widely different barycentric RV corrections.
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We demonstrate that the powerful disentangling technique used to separate the individual spectra of binary components and telluric lines can also be used to remove telluric lines from the spectrum of a single star by treating the telluric spectrum as a second star. We tested that on the spectra of alpha Boo (=Arcturus) secured with a Reticon detect...
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... and disentangled spectra differ from each other in the presence of the telluric lines in the observed spectrum. To demonstrate that it is indeed so, we compare the difference between the observed and disentangled spectrum with the KOREL disentangled spectrum of telluric lines -see Fig. 3. There is a very good correspondence between the two. In Fig. 4, two observed Reticon spectra of α Boo are compared to the KOREL disentangled spectrum of telluric lines. The two observed Reticon spectra were taken on HJD 2450152.5704 and 2450252.3465. They were chosen in order to have a large difference between the barycentric RV corrections. One can see better how the telluric lines affect the two ...
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At long-term count rate measurements of beta sources 3 H, 56 Mn, 32 Si, 36 Cl, 60 Co, 137 Cs, 90 Sr-90 Y and decay products of 226 Ra the rhythmic changes with amplitude 0.1% 0.3% from average magnitude and period 1 year, and up to 0.01 % with period about one month are detected. Magnitude of diurnal oscillations did not exceed 0.003%. Analysis of...
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... Moreover, it is not straightforward to mask off the forest of socalled 'micro-telluric' features which, though almost imperceptible, can nevertheless lead to RV contamination at the meter per second level, depending on factors including atmospheric water vapour content and airmass (Cunha et al. 2014). Correction using standard stars (Vacca, Cushing & Rayner 2003) or theoretical atmospheric transmission spectra models (Hrudková & Harmanec 2005;Bailey, Simpson & Crisp 2007;Cotton, Bailey & Kedziora-Chudczer 2014) is possible albeit non-trivial, and the results are imperfect. A recent and sophisticated effort to constrain telluric spectra directly from a large number of observed spectra has shown significant promise (Bedell et al. 2019, see also Section 7.2 of this paper). ...
Doppler spectroscopy is a powerful tool for discovering and characterizing exoplanets. For decades, the standard approach to extracting radial velocities (RVs) has been to cross-correlate observed spectra with a weighted template mask. While still widely used, this approach is known to suffer numerous drawbacks, and so in recent years increasing attention has been paid to developing new and improved ways of extracting RVs. In this proof-of-concept paper, we present a simple yet powerful approach to RV extraction. We use Gaussian processes to model and align all pairs of spectra with each other; we combine the pairwise RVs thus obtained to produce accurate differential stellar RVs, without constructing any template. Doing this on a highly localized basis enables a data-driven approach to identifying and mitigating spectral contamination, even without the input of any prior astrophysical knowledge. We show that a crude implementation of this method applied to an inactive standard star yields RVs with comparable precision to and significantly lower rms variation than RVs from industry-standard pipelines. Though amenable to numerous improvements, even in its basic form presented here our method could facilitate the study of smaller planets around a wider variety of stars than has previously been possible.
... Moreover, it is not straightforward to mask off the forest of so-called 'microtelluric' features which, though almost imperceptible, can nevertheless lead to RV contamination at the meter per second level, depending on factors including atmospheric water vapour content and air mass (Cunha et al. 2014). Correction using standard stars (Vacca et al. 2003) or theoretical atmospheric transmission spectra models (Hrudková & Harmanec 2005;Bailey et al. 2007;Cotton et al. 2014) is possible albeit non-trivial, and the results are imperfect. A recent and sophisticated effort to constrain telluric spectra directly from a large number of observed spectra has shown significant promise (Bedell et al. 2019, see also Section 7.2 of this paper). ...
Doppler spectroscopy is a powerful tool for discovering and characterizing exoplanets. For decades, the standard approach to extracting radial velocities (RVs) has been to cross-correlate observed spectra with a weighted template mask. While still widely used, this approach is known to suffer numerous drawbacks, and so in recent years increasing attention has been paid to developing new and improved ways of extracting RVs. In this proof-of-concept paper we present a simple yet powerful approach to RV extraction. We use Gaussian processes to model and align all pairs of spectra with each other; without constructing a template, we combine pairwise RV shifts to produce accurate differential stellar RVs. Doing this on a highly-localized basis enables a data-driven approach to identifying and mitigating spectral contamination, even without the input of any prior astrophysical knowledge. We show that a crude implementation of this method applied to an inactive standard star yields RVs with comparable precision to and significantly lower rms variation than RVs from industry-standard pipelines. Though amenable to numerous improvements, even in its basic form presented here our method could facilitate the study of smaller planets around a wider variety of stars than has previously been possible.
... Next, we multiplied the mean DAO stellar spectrum in the neighborhood of Hα by the mean spectrum of telluric lines, each time shifted in RV to the respective values of the heliocentric RV corrections. The multiplication is a better justified operation than summation because the telluric spectral lines do not have a continuum, thus the strength of the telluric line which absorbs at stellar continuum will be different from the strength of the same line absorbing in the strong stellar line (see the discussion on this topic in Hrudková &Harmanec 2005 andHadrava 2006). We omitted the spectrum with RJD52975.8496 ...
... Next, we multiplied the mean DAO stellar spectrum in the neighborhood of Hα by the mean spectrum of telluric lines, each time shifted in RV to the respective values of the heliocentric RV corrections. The multiplication is a better justified operation than summation because the telluric spectral lines do not have a continuum, thus the strength of the telluric line which absorbs at stellar continuum will be different from the strength of the same line absorbing in the strong stellar line (see the discussion on this topic in Hrudková &Harmanec 2005 andHadrava 2006). We omitted the spectrum with RJD52975.8496 ...
Bright Be star β CMi has been identified as a nonradial pulsator on the basis of space photometry with the Microvariability and Oscillations of Stars ( MOST ) satellite and also as a single-line spectroscopic binary with a period of 170.ͩ4. The purpose of this study is to re-examine both these findings using numerous electronic spectra from the Dominion Astrophysical Observatory, Ondřejov Observatory, Universitätssterwarte Bochum, archival electronic spectra from several observatories, as well as the original MOST satellite photometry. We measured the radial velocity of the outer wings of the double H α emission in all spectra at our disposal, and were not able to confirm significant radial-velocity changes. We also discuss the problems related to the detection of very small radial-velocity changes and conclude that while it is still possible that the star is a spectroscopic binary, there is currently no convincing proof of it from the radial-velocity measurements. Wavelet analysis of the MOST photometry shows that there is only one persistent (and perhaps slightly variable) periodicity of 0.ͩ617 of the light variations, with a double-wave light curve; all other short periods having only transient character. Our suggestion that this dominant period is the star’s rotational period agrees with the estimated stellar radius, projected rotational velocity, and with the orbital inclination derived by two teams of investigators. New spectral observations obtained in the whole-night series would be needed to find out whether some possibly real, very small radial-velocity changes cannot, in fact, be due to rapid line-profile changes.
... Then we multiplied the mean DAO stellar spectrum in the neighbourhood of Hα by the mean spectrum of telluric lines, each time shifted in RV to the respective values of the heliocentric RV corrections. The multiplication is a better justified operation because the telluric spectral lines do not have a continuum, thus the strength of the telluric line which absorbs at stellar continuum will be different from the strength of the same line absorbing in the strong stellar line (see the discussion on this topic in Hrudková &Harmanec 2005 andHadrava 2006). We omitted the spectrum with RJD 52975.8496 ...
... Then we multiplied the mean DAO stellar spectrum in the neighbourhood of Hα by the mean spectrum of telluric lines, each time shifted in RV to the respective values of the heliocentric RV corrections. The multiplication is a better justified operation because the telluric spectral lines do not have a continuum, thus the strength of the telluric line which absorbs at stellar continuum will be different from the strength of the same line absorbing in the strong stellar line (see the discussion on this topic in Hrudková &Harmanec 2005 andHadrava 2006). We omitted the spectrum with RJD 52975.8496 ...
Bright Be star beta CMi has been identified as a non-radial pulsator on the basis of space photometry with the MOST satellite and also as a single-line spectroscopic binary with a period of 170.4 d. The purpose of this study is to re-examine both these findings, using numerous electronic spectra from the Dominion Astrophysical Observatory, Ond\v{r}ejov Observatory, Universit\"atssterwarte Bochum, archival electronic spectra from several observatories, and also the original MOST satellite photometry. We measured the radial velocity of the outer wings of the double Halpha emission in all spectra at our disposal and were not able to confirm significant radial-velocity changes. We also discuss the problems related to the detection of very small radial-velocity changes and conclude that while it is still possible that the star is a spectroscopic binary, there is currently no convincing proof of it from the radial-velocity measurements. Wavelet analysis of the MOST photometry shows that there is only one persistent (and perhaps slightly variable) periodicity of 0.617 d of the light variations, with a double-wave light curve, all other short periods having only transient character. Our suggestion that this dominant period is the star's rotational period agrees with the estimated stellar radius, projected rotational velocity and with the orbital inclination derived by two teams of investigators. New spectral observations obtained in the whole-night series would be needed to find out whether some possibly real, very small radial-velocity changes cannot in fact be due to rapid line-profile changes.
We report a study exploring how the use of deep neural networks with astronomical Big Data may help us find and uncover new insights into underlying phenomena: through our experiments towards unsupervised knowledge extraction from astronomical Big Data we serendipitously found that deep convolutional autoencoders tend to reject telluric lines in stellar spectra. With further experiments we found that only when the spectra are in the barycentric frame does the network automatically identify the statistical independence between two components, stellar vs telluric, and rejects the latter. We exploit this finding and turn it into a proof-of-concept method for removal of the telluric lines from stellar spectra in a fully unsupervised fashion: we increase the inter-observation entropy of telluric absorption lines by imposing a random, virtual radial velocity to the observed spectrum. This technique results in a non-standard form of ‘whitening’ in the atmospheric components of the spectrum, decorrelating them across multiple observations . We process more than 250 000 spectra from the High Accuracy Radial velocity Planetary Search (HARPS) and with qualitative and quantitative evaluations against a database of known telluric lines, show that most of the telluric lines are successfully rejected. Our approach, ‘Stellar Karaoke’, has zero need for prior knowledge about parameters such as observation time, location, or the distribution of atmospheric molecules and processes each spectrum in milliseconds. We also train and test on Sloan Digital Sky Survey (SDSS) and see a significant performance drop due to the low resolution. We discuss directions for developing tools on top of the introduced method in the future.
Context. In-depth studies of exoplanetary atmospheres are starting to become reality. In order to unveil their properties in detail, we need spectra with a higher signal-to-noise ratio (S/N) and also more sophisticated analysis methods.
Aims. With high-resolution spectrographs, we can not only detect the sodium feature in the atmosphere of exoplanets, but also characterize it by studying its line profile. After finding a clearly w-shaped sodium line profile in the transmission spectrum of HD 189733b, we investigated the possible sources of contamination given by the star and tried to correct for these spurious deformations.
Methods. By analyzing the single transmission spectra of HD 189733b in the wavelength space, we show that the main sodium signal that causes the absorption in the transmission spectrum is centered on the stellar rest frame. We concentrate on two main stellar effects that contaminate the exoplanetary transmission spectrum: center-to-limb variations (CLVs) and stellar rotation. We show the effects on the line profile: while we correct for the CLV using simulated theoretical stellar spectra, we provide a new method, based directly on observational data, to correct for the Rossiter–McLaughlin contribution to the line profile of the retrieved transmission spectrum.
Results. We apply the corrections to the spectra of HD 189733b. Our analysis shows line profiles of the Na D lines in the transmission spectrum that are narrower than reported previously. The correction of the sodium D2 line, which is deeper than the D1 line, is probably still incomplete since the planetary radius is larger at this wavelength. A careful detrending from spurious stellar effects followed by an inspection in the velocity space is mandatory when studying the line profile of atmospheric features in the high-resolution transmission spectrum of exoplanets. Since the line profile is used to retrieve atmospheric properties, the resulting atmospheric parameters could be incorrectly estimated when the stellar contamination is not corrected for. Data with higher S/N coupled with improved atmospheric models will allow us to adapt the magnitude of the corrections of stellar effects in an iterative way.
Pythagoras of Samos (c. 569 − 475 BC) is best-known now for the Pythagorean Theorem relating the sides of a right triangle: \({a}^{2} + {b}^{2} = {c}^{2}\), but his accomplishments go far beyond this. When Pythagoras was a young man (c. 530 BC) he emigrated to Kroton in southern Italy where he founded the Pythagorean Brotherhood who soon held secular power over not just Kroton, but more extended parts of Magna Grecia. He and his followers were natural philosophers (they invented the term “philosophy”) trying to understand the world around them; in the modern sense we would call them scientists. They believed that there was a natural harmony to everything, that music, mathematics and what we now call physics were intimately related. In particular, they believed that the motions of the Sun, moon, planets and stars generated musical sounds. They imagined that the Earth is a free-floating sphere and that the daily motion of the stars and the movement through the stars of the Sun, moon and planets were the result of the spinning of crystalline spheres or wheels that carried these objects around the sky. The gods, and those who were more-than-human (such as Pythagoras), could hear the hum of the spinning crystalline spheres: they could hear the Music of the Spheres (see Koestler 1959).
As already discussed in Chapter 3, the three components of the Lagrangian displacement vector of an undamped oscillator contain a time-dependent factor exp( − i ωt), with ω = 2πν the angular frequency of the oscillation mode and \(\Pi = 2\pi /\omega = 1/\nu \) its period (see, e.g., Eq. (3.124) where it was explained that all Eulerian and Lagrangian perturbations contain a common factor). It is therefore clear that stellar oscillations give rise to periodic variations of the physical quantities. These translate into periodic variations of observables, such as the brightness, the colours, the radial velocity and the spectral line profiles. In this Chapter we describe methodology to derive the oscillation frequencies from time series of data of pulsating stars.
Global helioseismology is a mature field of research. Some models of the Sun agree with the helioseismic observations of the sound speed to within a fraction of a percent over 90% of the solar radius – a stunning achievement. Eddington’s longed-for “appliance” to pierce the outer layers of a star and see within has been discovered; with helioseismology we see the interior of the Sun. In addition, we understand solar nuclear fusion reactions so well that we reproduce them both explosively and non-explosively here on Earth, and we even believe that we now understand solar neutrinos, with cosmic implications. Thus the standard solar model can be elevated to “understood physics” – physics that will undergo small modifications in the future, but for which a revolutionary paradigm is unlikely.
Where do we go from here? It is important to remind ourselves that the Sun is but one star. Our model of it is exceedingly good, based on the bedrock of laboratory atomic and nuclear physics, mechanics and electromagnetism. We have a self-consistent model of one “experiment”: the Sun. As with all physics experiments, we need to alter the initial conditions and run the experiment again and again, searching parameter space, probing for weaknesses in the model, probing for new physical understanding, searching for unimagined discoveries.
We report in a series on the spectra of CH Cygni obtained in October 2004 in this paper. The spectra showed emission lines of H I, [O I], [O III], [N II], [Ne III] and Fe II: most of them became stronger than those obtained in April 2004. In order to retrieve the intrinsic emission profile, we removed the underlying M-type spectrum and telluric lines of O2 from the spectra. Then, we deconvoluted the resulting Hα and [O III] profiles into several Gaussian functions. Radial velocities of all lines observed in October 2004 were measured.Results are compared with those in April 2004, and are discussed by way of an accretion disk and a circumstellar model.
