scholarly journals Solar-like oscillations in η Boo

1995 ◽  
Vol 10 ◽  
pp. 337-338
Author(s):  
H. Kjeldsen ◽  
T. Bedding
Keyword(s):  
Power Spectrum ◽  
Equivalent Width ◽  
Window Function ◽  
The Sun ◽  
Optical Telescope ◽  
La Palma ◽  
Balmer Lines ◽  
Width Measurements ◽  
A New Technique ◽  
Low Dispersion

We have observed evidence for p-mode oscillations in the G0 IV star η Boo (V = 2.68). This represents the first clear evidence of solar-like oscillations in a star other than the Sun. We used a new technique in which we measure fluctuations in the temperature of the star via their effect on the equivalent width of the Balmer lines. The observations were obtained over six nights with the 2.5 m Nordic Optical Telescope on La Palma and consist of 13000 low-dispersion spectra. The upper part of Fig. 1 shows the power spectrum of the equivalent-width measurements (the inset shows the window function).

scholarly journals Asteroseismology from Equivalent Widths: A Test of the Sun

1998 ◽  
Vol 185 ◽  
pp. 375-378
Author(s):  
C.U. Keller ◽  
J.W. Harvey ◽  
S.C. Barden ◽  
M.S. Giampapa ◽  
F. Hill ◽  
...  
Keyword(s):  
Equivalent Width ◽  
The Sun ◽  
Low Resolution ◽  
Balmer Lines ◽  
Width Measurements ◽  
Low Amplitude

Kjeldsen et al. (1995) reported a probable detection of solar-like, low-amplitude p-mode oscillations in η Bootes using equivalent width measurements from low-resolution spectra of hydrogen Balmer lines. However, this detection has not been confirmed so far. Indeed, there is no confirmed detection of p-mode oscillations in a solar-like star using the equivalent width technique or any other approach (Bedding 1998).

scholarly journals Hunting for Stellar Coronal Mass Ejections

2016 ◽  
Vol 12 (S328) ◽  
pp. 198-203
Author(s):  
Heidi Korhonen ◽  
Krisztián Vida ◽  
Martin Leitzinger ◽  
Petra Odert ◽  
Orsolya Eszter Kovács
Keyword(s):  
Time Series ◽  
Coronal Mass Ejections ◽  
Detection Probability ◽  
Open Clusters ◽  
Occurrence Rate ◽  
Archival Data ◽  
The Sun ◽  
Late Type ◽  
Optical Telescope ◽  
Balmer Lines

AbstractCoronal mass ejections (CMEs) are explosive events that occur basically daily on the Sun. It is thought that these events play a crucial role in the angular momentum and mass loss of late-type stars, and also shape the environment in which planets form and live. Stellar CMEs can be detected in optical spectra in the Balmer lines, especially in Hα, as blue-shifted extra emission/absorption. To increase the detection probability one can monitor young open clusters, in which the stars are due to their youth still rapid rotators, and thus magnetically active and likely to exhibit a large number of CMEs. Using ESO facilities and the Nordic Optical Telescope we have obtained time series of multi-object spectroscopic observations of late-type stars in six open clusters with ages ranging from 15 Myrs to 300 Myrs. Additionally, we have studied archival data of numerous active stars. These observations will allow us to obtain information on the occurrence rate of CMEs in late-type stars with different ages and spectral types. Here we report on the preliminary outcome of our studies.

scholarly journals Abundance of Primordial Black Holes in Peak Theory for an Arbitrary Power Spectrum

2020 ◽  
Author(s):  
Chul-Moon Yoo ◽  
Tomohiro Harada ◽  
Shin’ichi Hirano ◽  
Kazunori Kohri
Keyword(s):  
Mass Spectrum ◽  
Power Spectrum ◽  
Environmental Effect ◽  
Window Function ◽  
Radial Coordinate ◽  
Primordial Black Holes ◽  
Scale Invariant ◽  
Curvature Perturbation ◽  
Arbitrary Power ◽  
Nonlinear Relation

Abstract We modify the procedure to estimate PBH abundance proposed in Ref. [1] so that it can be applied to a broad power spectrum such as the scale-invariant flat power spectrum. In the new procedure, we focus on peaks of the Laplacian of the curvature perturbation △ ζ and use the values of △ ζ and △ △ ζ at each peak to specify the profile of ζ as a function of the radial coordinate while the values of ζ and △ ζ are used in Ref. [1]. The new procedure decouples the larger-scale environmental effect from the estimate of PBH abundance. Because the redundant variance due to the environmental effect is eliminated, we obtain a narrower shape of the mass spectrum compared to the previous procedure in Ref. [1]. Furthermore, the new procedure allows us to estimate PBH abundance for the scale-invariant flat power spectrum by introducing a window function. Although the final result depends on the choice of the window function, we show that the k-space tophat window minimizes the extra reduction of the mass spectrum due to the window function. That is, the k-space tophat window has the minimum required property in the theoretical PBH estimation. Our procedure makes it possible to calculate the PBH mass spectrum for an arbitrary power spectrum by using a plausible PBH formation criterion with the nonlinear relation taken into account.

scholarly journals Precise Radial Velocity Measurements with a Cassegrain Spectrograph, I: Wavelength calibration

1999 ◽  
Vol 170 ◽  
pp. 63-67
Author(s):  
I. V. Ilyin ◽  
R. Duemmler
Keyword(s):  
High Resolution ◽  
Radial Velocity ◽  
Cross Correlation ◽  
Time Dependent ◽  
Instrumental Effects ◽  
Velocity Measurements ◽  
Echelle Spectrograph ◽  
Optical Telescope ◽  
La Palma ◽  
Observational Strategy

AbstractWe briefly describe the instrumental effects which affect the accuracy of the radial velocity measurements. We have implemented several methods to correct for the instability effects and improve the accuracy of the measurements. These include modifications of the observational strategy and a time-dependent wavelength solution as well as a discussion of the error of the offset from cross-correlation. These methods are applied to observations obtained with the high resolution échelle spectrograph SOFIN mounted at the Cassegrain focus of the alt-azimuth 2.56-m Nordic Optical Telescope, La Palma, Canary Islands.

scholarly journals Some aspects of the calculation of Balmer lines in the sun and stars

2002 ◽  
Vol 387 (2) ◽  
pp. 595-604 ◽  
Author(s):  
C. R. Cowley ◽  
F. Castelli
Keyword(s):  
The Sun ◽  
Balmer Lines

scholarly journals Oscillations in the Sun with SONG: Setting the scale for asteroseismic investigations

2019 ◽  
Vol 623 ◽  
pp. L9 ◽  
Author(s):  
M. Fredslund Andersen ◽  
P. Pallé ◽  
J. Jessen-Hansen ◽  
K. Wang ◽  
F. Grundahl ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Quality Data ◽  
Scaling Relations ◽  
The Sun ◽  
Average Amplitude ◽  
Echelle Spectrograph ◽  
High Quality ◽  
Data Set ◽  
High Quality Data ◽  
High Cadence

Context. We present the first high-cadence multiwavelength radial-velocity observations of the Sun-as-a-star, carried out during 57 consecutive days using the stellar échelle spectrograph at the Hertzsprung SONG Telescope operating at the Teide Observatory. Aims. Our aim was to produce a high-quality data set and reference values for the global helioseismic parameters νmax, ⊙ and Δν⊙ of the solar p-modes using the SONG instrument. The obtained data set or the inferred values should then be used when the scaling relations are applied to other stars showing solar-like oscillations observed with SONG or similar instruments. Methods. We used different approaches to analyse the power spectrum of the time series to determine νmax, ⊙: simple Gaussian fitting and heavy smoothing of the power spectrum. We determined Δν⊙ using the method of autocorrelation of the power spectrum. The amplitude per radial mode was determined using the method described in Kjeldsen et al. (2008, ApJ, 682, 1370). Results. We found the following values for the solar oscillations using the SONG spectrograph: νmax, ⊙ = 3141 ± 12 μHz, Δν⊙ = 134.98 ± 0.04 μHz, and an average amplitude of the strongest radial modes of 16.6 ± 0.4 cm s−1. These values are consistent with previous measurements with other techniques.

Quantifying SEM Resolution and Performance

1998 ◽  
Vol 4 (S2) ◽  
pp. 276-277
Author(s):  
David C Joy ◽  
Edgar Völkl
Keyword(s):  
Electron Microscope ◽  
Power Spectrum ◽  
Frequency Content ◽  
Signal To Noise ◽  
Transmission Electron ◽  
Width Measurements ◽  
And Performance ◽  
Set Up ◽  
Imaging Performance ◽  
Automated Line

The ability to reliably and quickly determine the resolution of the scanning electron microscope (SEM) is highly desirable becauseonly then can the level of performance which is being achieved be compared to that which was anticipated or specified. Further, in activities such as automated line width measurements, or in telemicroscopy, the ability to quantify the imaging performance provides the remote operator with the necessary information to monitor, document, and optimize the instrument set-up. However, compared to the equivalent task on the transmission electron microscope (TEM) an analysis of SEM performance is hampered by poor signal to noise ratios, and the absence of ideal ‘white noise’ samples.The two dimensional Fourier power spectrum of an image provides a readout of the frequency content of the information present in the micrograph. From an analysis of the power spectrum the highest spatial frequency transferred in the image can then be determined and hence the resolution of the micrograph can be specified.

Calculation of Equivalent Widths via an Interactive Display Device

1971 ◽  
Vol 11 ◽  
pp. 192-193
Author(s):  
Daniel A. Klinglesmith
Keyword(s):  
Computer Program ◽  
Equivalent Width ◽  
The Other ◽  
Display Device ◽  
Main Program ◽  
Interactive Display ◽  
Width Measurements ◽  
The Continuum ◽  
Light Pen

AbstractThis paper describes a computer program used to compute equivalent widths via an IBM 2250 attached to an IBM 360/75J.The measurement of stellar equivalent widths is a long tedious procedure and the final results depend to a large extent on where the stellar continuum is drawn. Therefore, a method which permits the continuum to be redrawn and the equivalent width remeasured quickly is desirable. An interactive CRT display device is an ideal instrument for allowing an astronomer to adjust the continuum level and the other parameters that are involved in equivalent width measurements. The display device discussed in this paper is an IBM model 2250 used in conjunction with a IBM 360/75J.The “2250” consists of a 12 inch (30 cm) square CRT display tube plus a 32 function key box, an alphanumeric keyboard and a light pen which can be pointed at any illuminated spot on the screen. Thus, there are 34 interrupts that can be sensed by the program controlling the “2250”. The program that has been used communicates with the astronomer via messages and questions displayed on the CRT screen. The main program remains in a wait state until one of the 34 possible interrupts occurs, whereupon it branches to the designated subroutine and executes the procedures necessary to satisfy the interrupt.

A NEW TECHNIQUE FOR THE STUDY OF SCATTER PROPAGATION IN THE TROPOSPHERE

1957 ◽  
Vol 35 (8) ◽  
pp. 823-830 ◽  
Author(s):  
J. H. Chapman ◽  
W. J. Heikkila ◽  
J. E. Hogarth
Keyword(s):  
Power Spectrum ◽  
Communication System ◽  
Carrier Frequency ◽  
Signal To Noise Ratio ◽  
Signal Strength ◽  
Noise Power ◽  
Signal To Noise ◽  
A New Technique ◽  
Conventional Signal ◽  
Noise Power Density

The power spectrum of the fluctuations in received signal strength on a near-optical U.H.F. circuit has been measured. The sidebands associated with these fluctuations can overlap the information-carrying sidebands of a communication system. When this happens, these sidebands must be taken into account in determining the signal-to-noise ratio of the system. In other words, the fluctuations then have the characteristics of noise, and therefore they are called propagation noise in the present paper. Experiments at a carrier frequency of 500 Mc. have shown that the propagation noise power density usually varies with sideband frequency ƒ (measured from the carrier) as 1/ƒ2, for f in the range 0.1 to 10 c.p.s. Departures from this law have been observed in the regions near 0.1 c.p.s. and 10 c.p.s. The measurement of the power spectrum directly offers several advantages over the conventional signal strength recording method, and these are discussed herein.

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