scholarly journals Li abundances and chromospheric activity of BY Dra type stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 343-344
Author(s):  
Tamara V. Mishenina ◽  
Caroline Soubiran ◽  
Valery V. Kovtyukh ◽  
Stanislav I. Belik
Keyword(s):  
Cross Correlation ◽  
Signal To Noise Ratio ◽  
Large Fraction ◽  
Ratio Method ◽  
Clear Correlation ◽  
High Signal ◽  
Echelle Spectrograph ◽  
Active Stars ◽  
Ionization Balance ◽  
Line Depth

AbstractAtmospheric parameters and Li abundances have been determined for 162 stars observed at high resolution, high signal to noise ratio with the ELODIE echelle spectrograph (OHP, France). Among them, about 70 stars are active stars with a large fraction of BY Dra type stars. For all stars, rotational velocities were obtained with a calibration of the cross-correlation function, effective temperatures by the line depth ratio method, surface gravities by the parallaxe method and by the ionization balance of iron. The frequency of stars with observed lithium is significantly higher in active stars than in non active stars. Among active stars, no clear correlation has been found between different indicators of activity for our sample stars, but some correlation of an index R′H K and vsini is observed.

scholarly journals A search for transiting planets in the β Pictoris system

2018 ◽  
Vol 615 ◽  
pp. A145 ◽  
Author(s):  
M. Mol Lous ◽  
E. Weenk ◽  
M. A. Kenworthy ◽  
K. Zwintz ◽  
R. Kuschnig
Keyword(s):  
Signal To Noise Ratio ◽  
Large Fraction ◽  
Young Star ◽  
High Signal ◽  
Data Set ◽  
Transiting Planets ◽  
Using Data ◽  
Exoplanet Systems ◽  
Transit Signals

Context. Transiting exoplanets provide an opportunity for the characterization of their atmospheres, and finding the brightest star in the sky with a transiting planet enables high signal-to-noise ratio observations. The Kepler satellite has detected over 365 multiple transiting exoplanet systems, a large fraction of which have nearly coplanar orbits. If one planet is seen to transit the star, then it is likely that other planets in the system will transit the star too. The bright (V = 3.86) star β Pictoris is a nearby young star with a debris disk and gas giant exoplanet, β Pictoris b, in a multi-decade orbit around it. Both the planet’s orbit and disk are almost edge-on to our line of sight. Aims. We carry out a search for any transiting planets in the β Pictoris system with orbits of less than 30 days that are coplanar with the planet β Pictoris b. Methods. We search for a planetary transit using data from the BRITE-Constellation nanosatellite BRITE-Heweliusz, analyzing the photometry using the Box-Fitting Least Squares Algorithm (BLS). The sensitivity of the method is verified by injection of artificial planetary transit signals using the Bad-Ass Transit Model cAlculatioN (BATMAN) code. Results. No planet was found in the BRITE-Constellation data set. We rule out planets larger than 0.6 RJ for periods of less than 5 days, larger than 0.75 RJ for periods of less than 10 days, and larger than 1.05 RJ for periods of less than 20 days.

scholarly journals SDSS-IV MaNGA: Bayesian analysis of the star formation history of low-mass galaxies in the local Universe

2020 ◽  
Vol 497 (4) ◽  
pp. 4753-4772
Author(s):  
Shuang Zhou ◽  
H J Mo ◽  
Cheng Li ◽  
Médéric Boquien ◽  
Graziano Rossi
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Signal To Noise Ratio ◽  
Large Fraction ◽  
Stellar Mass ◽  
Star Formation History ◽  
Radial Dependence ◽  
High Signal ◽  
Full Spectrum ◽  
Low Mass

ABSTRACT We measure the star formation histories (SFHs) of a sample of low-mass galaxies with M* < 109 M⊙ from the SDSS-IV MaNGA survey. The large number of IFU spectra for each galaxy are either combined to reach a high signal to noise ratio or used to investigate spatial variations. We use Bayesian inferences based on full spectrum fitting. Our analysis based on Bayesian evidence ratio indicates a strong preference for a model that allows the presence of an old stellar population, and that an improper model for the SFH can significantly underestimate the old population in these galaxies. The addition of near-infrared photometry to the constraining data can further distinguish between different SFH model families and significantly tighten the constraints on the mass fraction in the old population. On average more than half of the stellar mass in present-day low-mass galaxies formed at least 8 Gyr ago, while about 30 per cent within the past 4 Gyr. Satellite galaxies on average have formed their stellar mass earlier than central galaxies. The radial dependence of the SFH is quite weak. Our results suggest that most of the low-mass galaxies have an early episode of active star formation that produces a large fraction of their present stellar mass.

scholarly journals High Signal-To-Noise Ratio - the Spectroscopic Key to Algol Systems

1989 ◽  
Vol 107 ◽  
pp. 245-255
Author(s):  
Jocelyn Tomkin
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Signal To Noise Ratio ◽  
Large Fraction ◽  
High Signal ◽  
Signal To Noise ◽  
Algol System ◽  
Low Mass ◽  
Noise Ratio ◽  
Cno Abundances

AbstractThe usefulness of high signal-to-noise-ratio spectra for both radial-velocity and abundance studies of Algol systems is emphasised. It is shown that division by a hot star is a worthwhile step in pursuit of this objective. A preliminary analysis of high signal-to-noise-ratio, red and near-infrared, Reticon observations of R CMa shows that its primary has solar CNO abundances within the 0.3 dex observational error. The low-mass (0.17 m⊙) secondary of this Algol system must have lost a large fraction of its original mass. Some of this material would have been extensively processed during the secondary’s main-sequence lifetime and would therefore have had a highly non-solar CNO-abundance distribution. The lack of serious contamination of the primary’s abundances is consistent with most, but not all, plausible mass-transfer scenarios.

scholarly journals Nonradial pulsations in the open cluster NGC 3766

2009 ◽  
Vol 5 (S266) ◽  
pp. 518-521
Author(s):  
Rachael M. Roettenbacher ◽  
Ernest C. Amouzou ◽  
M. Virginia McSwain
Keyword(s):  
Signal To Noise Ratio ◽  
Large Fraction ◽  
Open Cluster ◽  
Spectroscopic Studies ◽  
High Resolution Spectroscopy ◽  
High Signal ◽  
Be Stars ◽  
B Stars ◽  
Be Star ◽  
Large Telescopes

AbstractNonradial pulsations (NRPs) are a proposed mechanism for the formation of decretion disks around Be stars. They are important tools to study the internal structure of stars. NGC 3766 has an unusually large fraction of transient Be stars, so it is an excellent location to study the formation mechanism of Be-star disks. High-resolution spectroscopy can reveal line-profile variations from NRPs, allowing measurements of both the degree, l, and azimuthal order, m. However, spectroscopic studies require large amounts of time with large telescopes to achieve the necessary high signal-to-noise ratio and time-domain coverage. On the other hand, multicolor photometry can be performed more easily with small telescopes to measure l only. Here, we present representative light curves of Be stars and nonemitting B stars in NGC 3766 from the CTIO 0.9m telescope in an effort to study NRPs in this cluster.

scholarly journals Chemical Composition of Planet-harboring Stars

2004 ◽  
Vol 202 ◽  
pp. 136-138
Author(s):  
G. Zhao ◽  
Y. Q. Chen ◽  
H. M. Qiu ◽  
S. K. Tang ◽  
Z. W. Li
Keyword(s):  
Chemical Composition ◽  
Signal To Noise Ratio ◽  
Giant Planet ◽  
Astronomical Observatory ◽  
High Signal ◽  
Chemical Abundance ◽  
Signal To Noise ◽  
Echelle Spectrograph ◽  
Abundance Patterns ◽  
High Metallicity

Based on the high-resolution, high signal-to-noise ratio spectra collected with the coudé echelle spectrograph attached to the 2.16m telescope at Beijing Astronomical Observatory, we determined the chemical abundance patterns for a sample of six planet-harboring stars. The result is used to investigate the connection between giant planet and high metallicity and to probe the influence of this process on other elements.

Photobleaching of fura-2 and its effect on determination of calcium concentrations

1987 ◽  
Vol 253 (4) ◽  
pp. C613-C618 ◽  
Author(s):  
P. L. Becker ◽  
F. S. Fay
Keyword(s):  
Spectral Properties ◽  
Signal To Noise Ratio ◽  
Large Error ◽  
Ratio Method ◽  
High Signal ◽  
Excitation Spectra ◽  
Excitation Light ◽  
Fura 2 ◽  
Dye Decomposition ◽  
Total Fluorescence

This study was performed to determine the effect of photobleaching on the spectral properties of the calcium-sensitive fluorescent dye fura-2. Fura-2, whether in cells or in calibrating solutions, was found to be bleached when exposed to excitation light. In contrast to the widely held belief, photobleaching altered the spectral properties of the dye. Decomposition of the excitation spectra of partially bleached fura-2 solutions revealed an intermediate that is still fluorescent and is not sensitive to calcium over the same range as fura-2, but which can bind calcium in the millimolar range. The presence of this intermediate violates one of the assumptions on which the ratio method of calibration is based; that is, that the only fluorescent species present are the calcium-bound and the free anion forms of fura-2. Thus, if photobleaching occurs, the ratio method will not give accurate calcium concentration values. We calculate that as little as an 8% loss of total fluorescence intensity is sufficient to produce a large error. Photobleaching of fura-2-loaded cells and fura-2 containing calibrating solutions can be minimized by reducing the oxygen concentration and by reducing the excitation light intensity. Strategies are presented to help maintain a high signal-to-noise ratio in fura-2 fluorescence detection systems, despite a lower excitation intensity so that photobleaching, and the resulting inaccuracies in calculated [Ca2+], can be largely avoided.

scholarly journals Comparison of Terrestrial and Lunar Time Scales by Giant Pulsar Impulses

2021 ◽  
Vol 65 (11) ◽  
pp. 1136-1144
Author(s):  
A. E. Rodin ◽  
V. V. Oreshko ◽  
V. A. Fedorova
Keyword(s):  
Time Scales ◽  
Cross Correlation ◽  
Arrival Time ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
The Moon ◽  
Recording Equipment ◽  
Giant Pulses ◽  
Cross Correlation Analysis ◽  
Pulse Arrival

Abstract We have developed a model for the time delay of pulse arrival between stations on the Moon and Earth. Comparison of the lunar and terrestrial time scales is proposed to be carried out by comparing the arrival time moments of giant pulses from pulsars. A method for such a comparison has been developed based on the cross-correlation analysis of the received pulses. Using the example of giant pulses from the pulsar PSR 0531+21, we showed that the error of comparing scales in the case of a high signal-to-noise ratio reaches a sub-discrete level and, thus, is determined by the reception band of the recording equipment.

scholarly journals Multiple stellar systems

1986 ◽  
Vol 118 ◽  
pp. 441-442
Author(s):  
A. Duquennoy ◽  
M. Mayor
Keyword(s):  
Radial Velocity ◽  
Small Amplitude ◽  
Cross Correlation ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Correlation Technique ◽  
Multiple Systems ◽  
Triple Systems ◽  
The Cross

A spectroscopic survey of visual binaries with known orbital elements has been carried out with the radial velocity scanner CORAVEL at the Haute-Provence Observatory, since 1977, (Baranne, Mayor, Poncet, 1979). This survey of more than 100 visual systems, selected from Dommanget's catalogue (1967) (see also a new edition 1982) was first devoted to the determination of stellar masses. Several multiple systems were detected and have permitted also a study of the structure of triple systems. We have detected and measured in particular a class of triple systems with radial velocity variations of small amplitude. Taking advantage of the high resolution and high signal-to-noise ratio accessible with the cross-correlation technique, such small amplitude radial velocity curves are sometimes derived only through the change of width and shape of the cross-correlation function. Let us recall that the cc-function of a SB2 (or SB3) system is only the weighted sum of the individual cc-functions (Mayor, 1985). This property of the cross-correlation combined with the linearity of the detector allow a very simple analysis of blended dips. The full width at half depth of the cross-correlation dip is about FWHD = 16 km/s (in absence of noticeable rotation). Analysis of blended systems allows a good determination of the two individual velocities if the difference |vr1 -Vr2| is equal or larger than about 0.15 *FWHD (about 2 km/s).

scholarly journals The Absolute Dimensions and Masses of IQ Persei

1985 ◽  
Vol 111 ◽  
pp. 389-389
Author(s):  
Claud H. Lacy
Keyword(s):  
Cross Correlation ◽  
Main Sequence ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Apsidal Motion ◽  
Orbital Elements ◽  
Photometric Observations ◽  
The Absolute ◽  
Motion Period ◽  
Absolute Dimensions

High signal-to-noise ratio spectrometric observations of the large light-ratio eclipsing binary IQ Per (B7 + A2) have been obtained with the coudé Reticon spectrograph of the 2.7 m reflector at McDonald Observatory. Absorption lines of the secondary are seen at the 4481 Å MgII line and the 4549 Å TiII + FeII blend. Radial velocities of both components have been measured by cross-correlation techniques and spectroscopic orbits have been computed. The fitted orbits have an eccentricity (0.075 ± 0.007) that is consistent with the photometric orbit of Hall, Gertken and Burke (1970). Young's (1975) “provisional” estimate of K2 is about 14% too small. Absolute dimensions and masses have been computed from Hall et al.'s (1970) photometric orbit and the new spectroscopic orbit. Additionally, V-R photometric observations obtained by M. Frueh at McDonald Obs. have been analysed by Popper with light curve synthesis techniques (WINK and EBOP). The relative radii of the new photometric orbits differ by less than 2% from the previous orbits, and the other orbital elements also show excellent agreement. The absolute dimensions and masses are (3.51 ± 0.04m⊙, 2.46 ± 0.04 R⊙) for the primary and (1.73 ± 0.02m⊙, 1.50 ± 0.03 R⊙) for the secondary. Both stars are near the zero-age main sequence. The value of ω has changed significantly between the epoch of Hall, Gertken, and Burke's (1970) observations and my own due to apsidal motion. The apsidal motion period is estimated to be in the interval 90 ≤ τ ≤ 180 yr.

scholarly journals Direction of Arrival Estimation Using Two Hydrophones: Frequency Diversity Technique for Passive Sonar

Sensors ◽  
2019 ◽  
Vol 19 (9) ◽  
pp. 2001 ◽  
Author(s):  
Peng Li ◽  
Xinhua Zhang ◽  
Wenlong Zhang
Keyword(s):  
Cross Correlation ◽  
Signal To Noise Ratio ◽  
Estimation Algorithm ◽  
Time Delay Estimation ◽  
High Signal ◽  
Frequency Diversity ◽  
Spectral Density Matrix ◽  
Processing Gain ◽  
The Cross ◽  
Diversity Technique

The traditional passive azimuth estimation algorithm using two hydrophones, such as cross-correlation time-delay estimation and cross-spectral phase estimation, requires a high signal-to-noise ratio (SNR) to ensure the clarity of the estimated target trajectory. This paper proposes an algorithm to apply the frequency diversity technique to passive azimuth estimation. The algorithm also uses two hydrophones but can obtain clear trajectories at a lower SNR. Firstly, the initial phase of the signal at different frequencies is removed by calculating the cross-spectral density matrix. Then, phase information between frequencies is used for beamforming. In this way, the frequency dimension information is used to improve the signal processing gain. This paper theoretically analyzes the resolution and processing gain of the algorithm. The simulation results show that the proposed algorithm can estimate the target azimuth robustly under the conditions of a single target (SNR = −16 dB) and multiple targets (SNR = −10 dB), while the cross-correlation algorithm cannot. Finally, the algorithm is tested by the swell96 data and the South Sea experimental data. When dealing with rich frequency signals, the performance of the algorithm using two hydrophones is even better than that of the conventional broadband beamforming of the 64-element array. This further validates the effectiveness and advantages of the algorithm.

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