scholarly journals The relative calibration of radial velocity for LAMOST medium resolution stellar spectra

2021 ◽  
Vol 21 (10) ◽  
pp. 265
Author(s):  
Jian-Ping Xiong ◽  
Bo Zhang ◽  
Chao Liu ◽  
Jiao Li ◽  
Yong-Heng Zhao ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Time Domain ◽  
Binary Stars ◽  
Zero Point ◽  
Systematic Difference ◽  
Variable Stars ◽  
Systematic Bias ◽  
Wavelength Calibration ◽  
Stellar Spectra ◽  
Medium Resolution

Abstract The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) started a median-resolution spectroscopic (MRS, R ∼7500) survey since October 2018. The main scientific goals of MRS, including binary stars, pulsators and other variable stars, were launched with a time-domain spectroscopic survey. However, the systematic errors, including the bias induced from wavelength calibration and the systematic difference between different spectrographs, have to be carefully considered during radial velocity measurement. In this work, we provide a technique to correct the systematics in the wavelength calibration based on the relative radial velocity measurements from LAMOST MRS spectra. We show that, for the stars with multi-epoch spectra, the systematic bias which is induced from the exposures on different nights can be corrected well for LAMOST MRS in each spectrograph. In addition, the precision of radial velocity zero-point of multi-epoch time-domain observations reaches below 0.5 km s−1. As a by-product, we also give the constant star candidates**, which can be the secondary radial-velocity standard star candidates of LAMOST MRS time-domain surveys.

scholarly journals Long-Term Coudé Radial-Velocity Studies With a 1.2-m Telescope

2001 ◽  
Vol 183 ◽  
pp. 283-288
Author(s):  
C.D. Scarfe
Keyword(s):  
Radial Velocity ◽  
Binary Stars ◽  
Star System ◽  
Standard Star ◽  
Stellar Spectra ◽  
Multiple Stars ◽  
Binary And Multiple Stars ◽  
Selection Of

AbstractI have used the 1.2-m telescope and coudé spectrograph of the Dominion Astrophysical Observatory for more than 30 years in a program of radial-velocity observations of binary stars. The program was begun with photographic plates as detectors, but for 20 years the primary detector has been the radial-velocity scanner, which cross-correlates stellar spectra with an artificial mask.Since some of the binaries under observation have periods of several years, the instrument’s stability is an important consideration. I have therefore been obliged to observe standard stars and asteroids to check its performance. These observations are of relevance to efforts to improve the IAU standard star system.I will describe the telescope, spectrograph and scanner, and will briefly discuss some of the results obtained for a selection of binary and multiple stars.

scholarly journals A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources

2019 ◽  
Vol 631 ◽  
pp. A118 ◽  
Author(s):  
Fabian Göttgens ◽  
Tim-Oliver Husser ◽  
Sebastian Kamann ◽  
Stefan Dreizler ◽  
Benjamin Giesers ◽  
...  
Keyword(s):  
Emission Line ◽  
Binary Stars ◽  
Globular Clusters ◽  
Cataclysmic Variables ◽  
Variable Stars ◽  
Emission Lines ◽  
Data Set ◽  
Stellar Spectra ◽  
X Ray ◽  
Emission Line Galaxies

Aims. Globular clusters produce many exotic stars due to a much higher frequency of dynamical interactions in their dense stellar environments. Some of these objects were observed together with several hundred thousand other stars in our MUSE survey of 26 Galactic globular clusters. Assuming that at least a few exotic stars have exotic spectra (i.e. spectra that contain emission lines), we can use this large spectroscopic data set of over a million stellar spectra as a blind survey to detect stellar exotica in globular clusters. Methods. To detect emission lines in each spectrum, we modelled the expected shape of an emission line as a Gaussian curve. This template was used for matched filtering on the differences between each observed 1D spectrum and its fitted spectral model. The spectra with the most significant detections of Hα emission are checked visually and cross-matched with published catalogues. Results. We find 156 stars with Hα emission, including several known cataclysmic variables (CV) and two new CVs, pulsating variable stars, eclipsing binary stars, the optical counterpart of a known black hole, several probable sub-subgiants and red stragglers, and 21 background emission-line galaxies. We find possible optical counterparts to 39 X-ray sources, as we detected Hα emission in several spectra of stars that are close to known positions of Chandra X-ray sources. This spectral catalogue can be used to supplement existing or future X-ray or radio observations with spectra of potential optical counterparts to classify the sources.

Coravel Measurements of IAU and Southern Potential Radial-Velocity Standard Stars. A Zero Point Discussion

1984 ◽  
Vol 88 ◽  
pp. 299-310
Author(s):  
M. Mayor ◽  
E. Maurice
Keyword(s):  
Radial Velocity ◽  
Observational Data ◽  
Zero Point ◽  
Variable Stars ◽  
Radial Velocities ◽  
Variable Velocity ◽  
Velocity Measurements ◽  
Similar Difference ◽  
Systematic Effects ◽  
Velocity Variations

AbstractRadial velocity measurements have been carried out since 1981 with the spectrometer CORAVEL at ESO, La Silla. Almost one thousand measurements of IAU radial velocity standard stars and of potential southern standard stars have been acquired by the different observers (mean precision per measurement 0.2 km/s).Among the measured IAU standard stars, at least four have shown clear radial-velocity variations from 1981 to 1984 (HD 36673, 156014, 44131, 115521).The comparison between CORAVEL mean velocities and IAU values reveals a difference of approximately 0.8 km/s between bright (mv <4.3) and faint IAU (mv >4.3) standards (Vr(IAUB) - Vr(IAUF) = +0.8 km/s). A similar difference also appears when comparing IAU standard velocities and those measured with the Victoria spectrometer, Fletcher et al. (1982).Thus, IAU standard stars not only include radial-velocity variable stars (intrinsic variables and SB) but they also present zero-point systematic effects.In the present paper we correct the radial velocities of the bright IAU standard stars so that they now belong to the same system as the faint ones. After elimination of variable velocity stars and stars showing large differences between IAU values and recent radial-velocity determinations, an homogeneous list of 34 IAU standard stars is obtained. These revised radial velocities are based on IAU values and new determinations obtained with the Victoria spectrometer and with CORAVEL at La Silla. These stars are distributed between the declinations δ = -82° and δ = +28°.This paper uses observational data in advance of the publication by CORAVEL observers of the 7th of the series of papers: “Radial velocities of southern stars obtained with the photoelectric scanner CORAVEL”.

scholarly journals An in-depth reanalysis of the alleged type Ia supernova progenitor Henize 2−428

2020 ◽  
Vol 638 ◽  
pp. A93 ◽  
Author(s):  
N. Reindl ◽  
V. Schaffenroth ◽  
M. M. Miller Bertolami ◽  
S. Geier ◽  
N. L. Finch ◽  
...  
Keyword(s):  
Light Curve ◽  
Radial Velocity ◽  
Zero Point ◽  
Asymptotic Giant Branch ◽  
Additional Absorption ◽  
Wavelength Calibration ◽  
Asymptotic Giant Branch Star ◽  
Diffuse Interstellar Bands ◽  
Type Ia ◽  
Supernova Type Ia

Context. The nucleus of the planetary nebula Hen 2-428 is a short orbital-period (4.2 h), double-lined spectroscopic binary, whose status as a potential supernova type Ia progenitor has raised some controversy in the literature. Aims. With the aim of resolving this debate, we carried out an in-depth reanalysis of the system. Methods. Our approach combines a refined wavelength calibration, thorough line-identifications, improved radial-velocity measurements, non-LTE spectral modeling, as well as multi-band light-curve fitting. Our results are then discussed in view of state-of-the-art stellar evolutionary models. Results. Besides systematic zero-point shifts in the wavelength calibration of the OSIRIS spectra which were also used in the previous analysis of the system, we found that the spectra are contaminated with diffuse interstellar bands. Our Voigt-profile radial velocity fitting method, which considers the additional absorption of these diffuse interstellar bands, reveals significantly lower masses (M1 = 0.66 ± 0.11 M⊙ and M2 = 0.42 ± 0.07 M⊙) than previously reported and a mass ratio that is clearly below unity. Our spectral and light curve analyses lead to consistent results, however, we find higher effective temperatures and smaller radii than previously reported. Moreover, we find that the red-excess that was reported before to prove to be a mere artifact of an outdated reddening law that was applied. Conclusions. Our work shows that blends of He II λ 5412 Å with diffuse interstellar bands have led to an overestimation of the previously reported dynamical masses of Hen 2−428. The merging event of Hen 2−428 will not be recognised as a supernova type Ia, but most likely leads to the formation of a H-deficient star. We suggest that the system was formed via a first stable mass transfer episode, followed by common envelope evolution, and it is now composed of a post-early asymptotic giant branch star and a reheated He-core white dwarf.

scholarly journals The HF Precise Radial Velocity Programme at DAO

1993 ◽  
Vol 139 ◽  
pp. 383-383
Author(s):  
S. Yang ◽  
A. Larson ◽  
A.W. Irwin ◽  
C. Goodenough ◽  
G.A.H. Walker ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Hydrogen Fluoride ◽  
Radial Velocities ◽  
Absorption Cell ◽  
Late Type ◽  
Wavelength Calibration ◽  
Stellar Spectra ◽  
Preliminary Results ◽  
Yield Information ◽  
Low Amplitude

AbstractA programme to measure precise radial velocities of late-type stars is being carried out at the 1.22-m telescope of the Dominion Astrophysical Observatory (DAO). Wavelength-calibration fiducials are imposed directly on the stellar spectra by passing the starlight through a controlled hydrogen fluoride (HF) absorption cell placed in front of the coude spectrograph. Presently, the primary targets of the programme are bright G, K, and M giants. Preliminary results confirm the low-amplitude, radial-velocity (RV) variability of the yellow giants discovered at the Canada-Prance-Hawaii telescope using the HF technique. These yellow giants and additional bright candidates are now being continually monitored at DAO. Preliminary results also indicate that the “yellow giant” variability extends to the early-M giants. In addition to the RV variations, the data also yield information on the simultaneous variability of the Ca II λ8662 line, Teff, as well as the R - I index of the stars.

scholarly journals The methods for searching hypervelocity star candidates from the SDSS

2013 ◽  
Vol 9 (S298) ◽  
pp. 421-421
Author(s):  
Yinbi Li ◽  
Ali Luo ◽  
Gang Zhao ◽  
Youjun Lu
Keyword(s):  
Black Hole ◽  
Velocity Distribution ◽  
Radial Velocity ◽  
Binary Stars ◽  
High Velocity ◽  
Main Sequence ◽  
Galactic Center ◽  
Main Sequence Stars ◽  
Massive Black Hole ◽  
Stellar Spectra

AbstractHyper-velocity stars are believed to be ejected out from the Galactic center through dynamical interactions of (binary) stars with the central massive black hole(s). In this paper, we firstly select F and G type main sequence stars from about 370,000 stellar spectra of DR7. Then, we select 369 high velocity stars from main sequence samples using the radial velocity distribution. Finally, we find 13 possible unbound hyper-velocity star candidates from the 369 high velocity stars.

scholarly journals Detection of Spectroscopic Triples

1992 ◽  
Vol 135 ◽  
pp. 161-163
Author(s):  
Tsevi Mazeh ◽  
Yuval Krymolowski ◽  
David W. Latham
Keyword(s):  
Binary System ◽  
Radial Velocity ◽  
Binary Stars ◽  
Halo Star ◽  
Stellar Spectra ◽  
Triple Systems ◽  
Secondary Star ◽  
Short Period ◽  
Cross Correlations ◽  
Orbital Solution

Several binary stars detected by the Center for Astrophysics (CfA) radial-velocity surveys were found to be members of triple systems. We present two examples, each requires a different analysis to discover its multiplicity.One example is G176-46, a double-lined halo star of the Carney & Latham (1987) high proper-motion survey. The secondary star (G176-46b) displays large radial velocity variations, in contrast with the primary (G176-46a), which is constant within the error limits. Figure 1 shows two cross correlations of the stellar spectra against the same calculated template taken at different times, which indicate that only the secondary’s peak changes its position. A similar variation was observed previously for ADS 8811 (Mazeh & Latham 1988).We have found the secondary radial velocity to vary with a period of 10.44 days, and therefore conclude that Gl76-46b is a member of a short-period binary system. The orbital solution has an amplitude of 38 km s−1 and eccentricity of 0.05.

scholarly journals LAMOST Time-Domain survey: first results of four K2 plates

2021 ◽  
Vol 21 (11) ◽  
pp. 292
Author(s):  
Song Wang ◽  
Hao-Tong Zhang ◽  
Zhong-Rui Bai ◽  
Hai-Long Yuan ◽  
Mao-Sheng Xiang ◽  
...  
Keyword(s):  
Time Domain ◽  
Binary Systems ◽  
Signal To Noise Ratio ◽  
Zero Point ◽  
Low Resolution ◽  
Parameter Estimations ◽  
Spatially Resolved ◽  
Medium Resolution ◽  
First Results ◽  
Parameter Values

Abstract From Oct. 2019 to Apr. 2020, LAMOST performed a time-domain (TD) spectroscopic survey of four K2 plates with both low- and medium-resolution observations. The low-resolution spectroscopic survey acquired 282 exposures ( ≈ 46.6 h) over 25 nights, yielding a total of about 767 000 spectra, and the medium-resolution survey took 177 exposures ( ≈ 49.1 h) over 27 nights, collecting about 478 000 spectra. More than 70%/50% of low-resolution/medium-resolution spectra have signal-to-noise ratio higher than 10. We determine stellar parameters (e.g., T eff, log g, [Fe/H]) and radial velocity (RV) with different methods, including LASP, DD-Payne and SLAM. In general, these parameter estimations from different methods show good agreement, and the stellar parameter values are consistent with those of APOGEE. We use the Gaia DR2 RV values to calculate a median RV zero point (RVZP) for each spectrograph exposure by exposure, and the RVZP-corrected RVs agree well with the APOGEE data. The stellar evolutionary and spectroscopic masses are estimated based on the stellar parameters, multi-band magnitudes, distances and extinction values. Finally, we construct a binary catalog including about 2700 candidates by analyzing their light curves, fitting the RV data, calculating the binarity parameters from medium-resolution spectra and cross-matching the spatially resolved binary catalog from Gaia EDR3. The LAMOST TD survey is expected to represent a breakthrough in various scientific topics, such as binary systems, stellar activity, stellar pulsation, etc.

The study of short orbital period of delta scuti pulsating variable stars

2019 ◽  
Vol 15 (S356) ◽  
pp. 407-407
Author(s):  
Abduselam Mohammed
Keyword(s):  
Time Delay ◽  
Orbital Period ◽  
Binary Stars ◽  
Arrival Time ◽  
Periodic Variation ◽  
Variable Stars ◽  
Orbital Elements ◽  
Pulsating Stars ◽  
Delta Scuti ◽  
Arrival Time Delay

AbstractAs a pulsating star moves in its binary orbit, the path length of the light between us and the star varies, leading to the periodic variation in the arrival time of the signal from the star to us (earth). With the consideration of pulsators light arrival time delay effects several new methods which allows using Kepler photometric data (light curves) alone to find binary stars have been recently developed. Among these modern techniques we used binarogram method and we identified that several δSct pulsating stars have companions. The application of these method on detecting long periods(i.e. longer than about 50 d) δSct pulsating stars is not new, but the uniqueness of this study is we verified that it is also applicable to detect and determine the orbital elements of short periods (i.e short orbital period) δSct pulsating stars. With this investigation, we identified the possible way to overcome effects of fictious peaks, even, on the maximum peaks helpful to verify weather the star has companion or not depend up on the existence of the time-delay. Then, we applied the technique on known binary stars and their orbital elements are previously published. Finally, we identified some new short orbital period δSct pulsating stars and obtained their orbital frequency and period with the same procedures. Because of with our attempts we succeeded and verified the applicability of the method (the Binarogram method) on these stars (i.e short orbital period) for the first time, we expect that our present study will play a great role for similar study and to improve our binary statistics.

scholarly journals R Coronae Borealis Stars: Long-Term Photometric & Spectroscopic Studies

1998 ◽  
Vol 11 (1) ◽  
pp. 379-379
Author(s):  
P.L. Cottrell ◽  
L. Skuljan ◽  
P.M. Kilmartin ◽  
C. Gilmore ◽  
W.A. Lawson
Keyword(s):  
Radial Velocity ◽  
Spectroscopic Studies ◽  
Photometric Data ◽  
Decline Phase ◽  
Dust Clouds ◽  
Medium Resolution ◽  
Formation And Evolution ◽  
R Coronae Borealis Stars ◽  
Insight Into

For more than a decade we have been able to acquire and analyse a significant amount of photometric data of the highly variable R Coronae Borealis (RCB) stars. This has made been possible by a photometric service observing programme instigated at the Observatory. These photometric data have been combined with less extensive spectroscopic coverage, particularly of the decline phase of these stars. These have been supplemented by observations obtained at Mount Stromlo and Siding Spring Observatories for a radial velocity study. Significantly more spectroscopic observations are now being acquired with the development of a new medium resolution spectrograph at Mount John University Observatory. In this poster we will present recent photometric and spectroscopic results for a number of the RCB stars in our sample. This observational and analysis work can be used to provide further insight into the nature of these stars, their likely progeny and progenitors and the processes that are involved in the formation and evolution of the obscuring dust clouds which cause the decline phase.

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