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An Apparent Dependence of the Apex and Velocity of Solar Motion, as Determined from Radial Velocities, Upon Proper Motion. C. D. Perrine. Author information.
Table of contents

Not Available Late-type stars and magnetic activity. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.

Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data. Radial velocities have beendetermined for B8-F2 stars, being new. The catalogue contains entries yielding an average detection rate of Inaddition to count rates, source detection parameters, hardness ratios,and X-ray fluxes we also list X-ray luminosities derived from Hipparcosparallaxes. Catalogue also available at CDS via anonymous ftp tocdsarc. We have derived the stellar ages from fivedifferent age estimators: the location in the HR diagram compared totheoretical isochrones, the rotational velocity, the strength ofchromospheric calcium emission lines, the stellar metallicity, and theirspace velocity.

New calibrations consistent with recent theoreticalisochrones are provided for the last four indicators. For hot stars,isochrones are the best indicator, while stellar rotation is best forcool stars. However, many stars require in fact a combination ofdifferent methods to properly bracket their actual age.

ASTR 5610 (Majewski) Lecture Notes

We also discussthe uncertainties involved, in particular those in using isochrones, andwe find that these uncertainties are often underestimated in theliterature. Chromospheric models for late A-type stars The chromospheres of alpha Aql Altair and alpha Cep Alderamin areinvestigated. Different semi-empirical model atmospheres areconstructed, and the predicted spectra are compared to the observationsof the hydrogen Lyman-alpha line IUE and carbon both neutral andionized multiplets GHRS-HST. Provisional referencemodels are proposed for alpha Aql. The lower emission of alpha Cep withrespect to alpha Aql is better explained by a difference of column massthan by a difference of temperature.

For both stars, therelatively narrow dips of the C ii emission feature cannot be of stellarorigin, owing to the fast rotation, but of interstellar absorptionnature. The catalogue contains entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes.

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The catalogue isalso available in electronic form via anonymous ftp tocdsarc. The determinations are based onnarrow and wide band photometric data obtained for this purpose, andtake into account previously published narrow-band measures oftemperature. Regression coefficients are given for relations between thedetermined temperatures and the photometric parameters B2-V1 , b-y and B-V , corrected for interstellar extinction through use ofHipparcos parallaxes. A correction for the effect of metallicity on thedetermination of integrated flux is proposed. The importance of aknowledge of metallicity in the representation of derived temperaturesfor Class V, IV and III stars by empirical functions is discussed andformulae given.

An estimate is given for the probable error of eachtemperature determination. These observations are part of a study of the onset ofmagnetic surface activity along the main sequence. Values for theeffective temperature, surface gravity and interstellar reddening havebeen obtained from a comparison of the observed Walraven colours withtheoretical values.


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Are metallic A-F giants evolved AM stars? If this hypothesis is right, Am and metallic A-FIII starsneed to have the same rate of binaries and a similar distribution ofvsin i. From our new spectroscopic data and from vsin i and radialvelocities in the literature, we show that it is not the case. Themetallic giant stars are often fast rotators with vsin i larger than kms -1 , while the maximum rotational velocity for Am stars is about kms Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques.

The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects.

ASTR , Majewski [SPRING ]. Lecture Notes

The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method IRFM using the large sample of comparison stars.

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However,there is also evidence for somewhat significant differential effects. These include an average systematic shift of 2. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata.

Table 1 and 2 are only available in the electronic form of thispaper The Angular Momentum of Main Sequence Stars and Its Relation to Stellar Activity Rotational velocities are reported for intermediate-mass main sequencestars it the field.

We analyze these rotation rates for a dependence on bothmass and age. We compare the average rotation speeds of the field starswith mean velocities for young stars in Orion, the Alpha Persei cluster,the Pleiades, and the Hyades. Less massive stars in the range betwee n1. The magnetic activity implicated in the rotational spindown ofthe Sun and of similar stars during their main sequence lifetimes mus ttherefore play only a minor role in determining the rotation rates ofthe intermediate mass stars, either because a solar-like dynamo is weakor absent, or else the geometry of the magnetic field is appreciablyless effective in removing angular momentu m from these stars.

In either case, the micrometer will determine the speed. If it is desired that the comparison spectrum be that of hydrogen or other gas, the current from a Ruhmkorff coil passed through a Pliicker tube containing the gas may form the light source. The arc spectrum of iron, titanium, or other metal, which does not utilize the coil and jar, has its advantages, and is preferred by many observers.

We have referred to one or two of the larger problems of the stellar system which we hope soon to solve from radial velocity data. Before planning extensive structures, such as 22 It should not be inferred that the light from an electric arc or spark is merely a temperature effect. There concerns us the question of what celestial objects are available for radial velocity observation. We shall pass in hasty review the chief types of stellar and other spectra, explaining briefly the possibilities and limita- tions of each type, for our present purposes.

The number of bodies visible in our great telescopes is of the order of one hundred million; and many more, perhaps twice this number, can be recorded photographically by existing instruments. It is a thesis of great value that all celestial bodies — the nebuls, the bright stars, and the invisible bodies — are related products of a system of sidereal evolution.

The general course of the evolutionary process, as applied to the principal classes of celestial bodies, is thought to be fairly well known.

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We think we are able to group these classes, with little chance of serious error, in the order of their effective ages. Fraunhofer's discovery of the dark lines in the solar spectrum has already been referred to. To his genius also we owe the first studies of stellar spectra. He recognized clearly, in , that there are different types of stellar spectra. Im Spectrum vom Lichte des Sirius vermochte ich nicht, in dem Orange und in der gelben Farbe fixe Linien wahrzunehmen ; im Griinen dagegen ist ein sehr starker Streifen zu erkennen, und zwei andere ungemein starke Streifen sind im Blauen, die keiner der Linien vom Planetenlichte ahnlich zu seyn scheinen; wir haben ihren Ort mit dem Micrometer bestimmt.

Castor giebt ein Spectrum, welches dem des Siriiis gleicht; der Streifen im Griinen hat, dee schwachen Lichtes ungeachtet, Intensitat genug, dass ich ihn messen konnte, und ich fand ihn genau an demselben Orte wie beim Sirius, Die Streifen im Blauen konnte ich zwar erkennen, doch war das Licht nicht stark genug, um ihren Ort zu bestimmen.

Introduction

Secchi 's spectroscopic survey of the sky, about , which included an examination of the spec- tra of many hundreds of stars down to the sixth magnitude, led him to a remarkable classification of stellar spectra, which was exceedingly useful to students of the stars during the succeeding third of a century. Ich sah die Linie D sehr gut; sie ist genau an dem Orte wie bei Planetenlicht. Capella giebt ein Spectrum, in welchem sich an den Orten D und b dieselben fixen Linien zeigen als in dem aus Sonnen- licht.

Das Spectrum von Beteigeuee enthalt zahlreiche fixe Linien, die bei guter Luft scharf begranzt sind, und wenn es gleich beim ersten Anblick keine Aehnlichkeit mit dem Spectrum der Venus zu haben scheint, so finden sich doch genau an den Orten, wo bei Sonnenlicht D und b sind, auch in dem Spectrum dieses Fizsternes ahnliche Linien. Im Spectrum von Procyon erkennt man mit Muhe einige Linien, und nicht so deutlich, dass man mit Sicherheit ibren Ort bestimmen konnte. Ich glaube im Orange an dem Ort D eine Linie gesehen zu haben.

The spectra of all these stars consist of an almost uniform prismatic series of colours, interrupted only by four very strong black lines. Of these black lines the one in the red is coincident with the solar line G of Fraunhofer; another, in the blue, coin- cides with the line F; the other two are also in the Sun's spectrum, but they have no prominent place. For the purposes of these lectures, we may describe Secchi's system very briefly, as follows : Type I.

This type includes the so-called white stars, whose spectra are relatively rich in blue and violet light, such as Sirius, VegUy Regulus and the stars in the Big Dipper a UrscB Majoris excepted. This type of spectrum is characterized by strong absorption lines of hydrogen and the essential absence or scarcity of metallic lines. Half of the bright stars, more or less, are of Type I. Type II. Huggins, and also lately by myself "Stars of this first type are very numerous, and embrace almost one- half of the visible stars of the heavens.