Radial Velocity Variability of K Giants

1991 ◽  
Vol 130 ◽  
pp. 386-388
Author(s):  
Artie P. Hatzes ◽  
William D. Cochran
Keyword(s):  
Radial Velocity ◽  
Active Regions ◽  
Peak Amplitude ◽  
Short Term ◽  
Rotational Modulation ◽  
Surface Active ◽  
Radial Velocity Data ◽  
Long Term Variations ◽  
K Giants

AbstractAt McDonald Observatory we have been monitoring the relative radial velocities of a sample of K giants. The technique employed uses the telluric O2 lines near 6300 Å as a reference for measuring the stellar line shifts. We demonstrate that precisions of 10 m s−1 are possible with this technique. We present radial velocity data covering a 2 year time span for α Boo, α Tau, and β Gem. All of these stars show both long term variations (~ several hundred days) with a peak-to-peak amplitude of about 400 m s−1 and short term variations (~ few days) with a peak-to-peak amplitude of about 100 m s−1. The long term variations may be due to the rotational modulation of surface active regions whereas the short term variations may be indicative of pulsations.

scholarly journals A Transient Shock-Wave in the Shell of the Be Star HD 184279

1987 ◽  
Vol 92 ◽  
pp. 95-98
Author(s):  
D. Ballereau ◽  
J. Chauville
Keyword(s):  
Shock Wave ◽  
Radial Velocity ◽  
Emission Spectrum ◽  
Short Term ◽  
Balmer Series ◽  
Spectroscopic Observations ◽  
The Past ◽  
Be Star ◽  
Long Term Variations

HD 184279 (V1294 Aql) has presented in the past an emission spectrum on the first terms of the Balmer series, and shell absorptions on the hydrogen and neutral helium lines. Their variations have been reported by Merrill (1952), Merrill and Lowen (1953) and Svolopoulos (1975). Ballereau and Hubert-Delplace (1982) evidenced long-term V/R variations with an amplitude of ∼100 km s-1. Short-term photometric variations are irregular (Tempesti and Patriarca, 1976), while long-term variations are correlated with radial velocity (RV) of shell lines (Horn et al., 1982). Ballereau and Chauville (in preparation) extended the spectroscopic observations until 1984 and confirmed the pseudo-periodic variations, the last half-period ranging over 3.4 years (April 1, 1980-August 1, 1983).

scholarly journals The Long-term Variation in the RV Tauri Star U Mon

1995 ◽  
Vol 155 ◽  
pp. 409-410 ◽  
Author(s):  
Karen R. Pollard ◽  
P. L. Cottrell
Keyword(s):  
High Resolution ◽  
Light Curve ◽  
Radial Velocity ◽  
Tauri Star ◽  
Short Term ◽  
Instability Strip ◽  
Term Variation ◽  
Velocity Variations

The RV Tauri stars are semiregular pulsating variables located in the brightest part of the Cepheid II instability strip. They have a characteristic light curve of alternating deep and shallow minima. A subset of the RV Tauri stars (the RVb subclass) exhibit long-term (500 to 2600 day) light and radial velocity variations. Although it is well established that the short-term variations are due to pulsations, the long-term behaviour is not well understood.BVRI photometry and high-resolution spectra of U Mon (the brightest member of the RVb subclass) were obtained at the Mt John University Observatory (MJUO) between 1990 Aug and 1994 May. The light and colour curves obtained clearly show the long-term variation in U Mon (Fig. 1(a) and (b)). The reddest colours occur slightly later than the long-term minimum in the light curve. The short-term light and colour variations are ‘damped’ at the long-term minimum.

scholarly journals An ultra-short period rocky super-Earth orbiting the G2-star HD 80653

2020 ◽  
Vol 633 ◽  
pp. A133 ◽  
Author(s):  
G. Frustagli ◽  
E. Poretti ◽  
T. Milbourne ◽  
L. Malavolta ◽  
A. Mortier ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Thermal Emission ◽  
Earth Planet ◽  
Period Orbit ◽  
Short Period ◽  
Orbital Phase ◽  
Solar Type ◽  
Radial Velocity Data

Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample of such planets that have accurate and precise masses and radii, which also includes estimates of the level of irradiation and information about possible companions. Here we report a detailed characterization of a USP planet around the solar-type star HD 80653 ≡EP 251279430 using the K2 light curve and 108 precise radial velocities obtained with the HARPS-N spectrograph, installed on the Telescopio Nazionale Galileo. From the K2 C16 data, we found one super-Earth planet (Rb = 1.613 ± 0.071 R⊕) transiting the star on a short-period orbit (Pb = 0.719573 ± 0.000021 d). From our radial velocity measurements, we constrained the mass of HD 80653 b to Mb = 5.60 ± 0.43 M⊕. We also detected a clear long-term trend in the radial velocity data. We derived the fundamental stellar parameters and determined a radius of R⋆ = 1.22 ± 0.01 R⊙ and mass of M⋆ = 1.18 ± 0.04 M⊙, suggesting that HD 80653 has an age of 2.7 ± 1.2 Gyr. The bulk density (ρb = 7.4 ± 1.1 g cm−3) of the planet is consistent with an Earth-like composition of rock and iron with no thick atmosphere. Our analysis of the K2 photometry also suggests hints of a shallow secondary eclipse with a depth of 8.1 ± 3.7 ppm. Flux variations along the orbital phase are consistent with zero. The most important contribution might come from the day-side thermal emission from the surface of the planet at T ~ 3480 K.

Morphology and Pipeline Design Through a Dynamic Landfall Area: The Black Sea Pipeline Case

2002 ◽  
Author(s):  
Z. Chen ◽  
Marco Venturi ◽  
R. Bijker
Keyword(s):  
Sediment Transport ◽  
Environmental Impact ◽  
Black Sea ◽  
Morphological Changes ◽  
The Black Sea ◽  
Burial Depth ◽  
Short Term ◽  
Pipeline Route ◽  
Long Term Variations

The Blue Stream pipeline project is a gas transportation system for the delivery of processed gas from a gas station in the southern Russia across the Black Sea to Ankara, Turkey. The Turkish landfall of the offshore pipeline in the Black Sea is located near Samsun, see Figure 1 for the pipeline route. One of the main aspects of the design of pipeline through a morphologically dynamic area such as landfall is the required burial depth (Chen et al, 1998, 2001 and Bijker et al 1995). The burial depth is the result of an optimisation between: • safety of the pipeline (which often requires a large burial depth), and • environmental impact and trenching costs (a small burial depth means less dredging and less environmental impact). This paper presents a method of predicting the future extremely low seabed level in a morphologically dynamic landfall area, which is required to determine the burial depth of the pipeline. Both short term and long term coast evolution were assessed to quantify the expected lowest seabed level along the pipeline route in the landfall area during the pipeline lifetime of 50 years. The results were used to determine the required pipeline burial depth. The long term morphological changes originate from long term variations in the morphological system (e.g. river input), gradient in the longshore sediment transport and long term variations in the hydrodynamic conditions. The short-term morphological changes originate from beach profile variations due to cross-shore sediment transport as a result of seasonal and yearly variations in the wave and current conditions. Numerical modelling was applied to compute the longshore and cross-shore sediment transport rates and the resulting coastline evolution and cross-shore profile evolution. The longshore transport model was validated using the available data on the coastline changes in the past 20 years, which was derived from the satellite images. The 50-year lowest seabed level has been determined as the sum of the coastline retreat and the cross-shore evolution in the next 50 years.

Animal Protein and Rational Choice: Diet in the Eighteenth Century

2014 ◽  
Vol 44 (4) ◽  
pp. 427-452 ◽  
Author(s):  
Martin Bruegel ◽  
Jean-Michel Chevet ◽  
Sébastien Lecocq
Keyword(s):  
Eighteenth Century ◽  
Rational Choice ◽  
Choice Model ◽  
Meat Consumption ◽  
Short Term ◽  
Rational Choice Model ◽  
Elite Status ◽  
Changing Patterns ◽  
Long Term Variations

Analysis of the account books of the convent school of Saint-Cyr between 1688 and 1788 reveals the causes of the institution's changing patterns of meat consumption. Although a rational-choice model can explain short-term variations in the school's diet, economic variables alone are not sufficient to explain its long-term variations, as evolving tastes began to infiltrate Saint-Cyr's traditional, aristocratic diet. The unintended side effect of this development was to improve nutrition, which the school managed to do without running afoul of claims to elite status.

scholarly journals Ambiguities in the classification of Cochin Estuary, West Coast of India

2013 ◽  
Vol 10 (3) ◽  
pp. 3595-3628 ◽  
Author(s):  
A. Shivaprasad ◽  
J. Vinita ◽  
C. Revichandran ◽  
N. T. Manoj ◽  
K. V. Jayalakshmy ◽  
...  
Keyword(s):  
Data Sets ◽  
Dry Period ◽  
Cochin Estuary ◽  
Short Term ◽  
Classification Schemes ◽  
Biological Features ◽  
High Runoff ◽  
Long Term Variations

Abstract. Cochin Estuary is a unique complex system along Indian coastline with a widespread area at the upstream. The fluctuations in salinity are of extreme kind ranging from entirely riverine to entirely saline. The high runoff months are characterized by monsoonal spells causing intense flushing. During the peak dry period, the runoff is less but steady providing a stable environment. River runoff is controlled by short term variations rather than long term variations. Using large comprehensive data sets, an attempt is made to evaluate several classification schemes for the estuary. The existing methods proved to be insufficient to represent the real salient features of this typical estuary. Arguments are also presented to illustrate the confusion in the names by which the estuary is commonly known. Therefore, a new nomenclature is proposed as "Cochin Monsoonal Estuarine Bay" embodying the physiographic, hydrographic and biological features of the estuary.

Variations in amplitude and time course of inhibitory postsynaptic currents

1986 ◽  
Vol 56 (5) ◽  
pp. 1424-1438 ◽  
Author(s):  
D. Gardner
Keyword(s):  
Time Constant ◽  
Decay Time ◽  
Time Course ◽  
Decay Time Constant ◽  
Peak Amplitude ◽  
Short Term ◽  
Presynaptic Neuron ◽  
Inhibitory Postsynaptic Currents ◽  
Postsynaptic Currents

In order to examine the relative contributions of changes in amplitude and time course to synaptic plasticity, variations in peak amplitude and time constant of decay have been analyzed from inhibitory postsynaptic currents (PSC) recorded in voltage-clamped Aplysia buccal ganglia neurons. In these cells, synaptic currents with single time constant decay can be recorded with low noise under well-controlled space clamp. Over a population of 36 neurons, duration was more narrowly distributed than amplitude, but each varied. The coefficient of variation (CV) was 0.21 for decay time constant (tau) and 0.87 for peak conductance (g peak). Population variances are larger than can be accounted for by such variables as temperature and noise amplitude, suggesting that functional modifications alter each of these determinants of synaptic effectiveness over the long term. Recordings of up to several hundred PSC in each of 16 neurons show that both PSC amplitude and time course recorded in a single cell can vary independently over short time spans. Decay remained single exponential as time course changed. CV for tau averaged 0.11; CV for g peak was 0.19. Variability of tau was not an artifact of amplitude; CV was relatively uncorrelated with current amplitudes or sample size. Smoothing and adding excess noise to each individual PSC of a set produced only small changes to CV, showing that variability was not an artifact of noise. Several specific manipulations of the presynaptic neuron altered both PSC amplitude and time course. Tetanic stimulation of the presynaptic neuron produced short-term potentiation of both amplitude and time course of subsequent PSCs. Peak amplitude was increased by 80%; tau by 12%. Reducing interspike intervals from 10 to 1 s produced habituation of both amplitude and time course, with g peak decreasing by 35 to 40% and tau by 10%. Conditioning DC depolarization of the presynaptic neuron enhanced PSC amplitude with little effect on decay time constant. Although short-term plastic changes affect PSC amplitude more than duration, each is alterable. Parallel changes in both can synergistically alter synaptic charge transfer, and therefore efficacy. Similar mechanisms may produce larger long-term differences seen between neurons.

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