IIA Library  

Stellar rotation (Record no. 10727)

MARC details
000 -LEADER
fixed length control field 07986nam a2200241Ia 4500
003 - CONTROL NUMBER IDENTIFIER
control field IN-BaIIA
005 - DATE AND TIME OF LATEST TRANSACTION
control field 20211109150031.0
008 - FIXED-LENGTH DATA ELEMENTS--GENERAL INFORMATION
fixed length control field 211028s9999 xx 000 0 eng d
040 ## - CATALOGING SOURCE
Transcribing agency IIA Library
080 ## - UNIVERSAL DECIMAL CLASSIFICATION NUMBER
Universal Decimal Classification number 043:524.3-54
Item number MAT
100 ## - MAIN ENTRY--PERSONAL NAME
Personal name Mathew, Annamma
9 (RLIN) 18296
Relator term Author
245 #0 - TITLE STATEMENT
Title Stellar rotation
Remainder of title effects of rotation on colours and line Indices of stars
Statement of responsibility, etc. Annamma Mathew
Medium [Ph.D Thesis]
260 ## - PUBLICATION, DISTRIBUTION, ETC.
Place of publication, distribution, etc. Bangalore
Name of publisher, distributor, etc. Indian Institute of Astrophysics
Date of publication, distribution, etc. 1993
300 ## - PHYSICAL DESCRIPTION
Extent xi,137p
502 ## - DISSERTATION NOTE
Degree type Doctor of Philosophy<br/>
Name of granting institution Indian Institute of Astrophysics, Bangalore
Year degree granted 1993
520 ## - SUMMARY, ETC.
Summary, etc. The effect of rotation on colours and line indices of stars has been a subject of<br/>some controversy, though not actually apprecia.ted as such. Empirica} calibra.tions<br/>of broad band and narrow band indices available in the literature have all been<br/>carried out without taking rotation effects into account. (e.g. u v b y and (ß<br/>by Crawford 1978, 1979). The discordant results in this field until 1970 have<br/>been nicely summarised by Collins (1970). The basic reason, that rotation effects<br/>on colours and line indices of stars could not be established firmly, seems to be<br/>due to the smallness of the effect at. ll10dprte rotational velocities. Further, the<br/>effects on observed indices by other such as duplicity, chemical peculiarity,<br/>evolutionary effects and variable interstellar extinction appear to have introduced<br/>a large uncertainity in the determination of rotation effects.<br/>The problem is further complicated by the fact that the effects are a function<br/>of the mass of the stars. Theoretical work especially by Collins and his collaborators<br/>shows that each index is affected differently and very large effects shoud<br/>be observable for the A stars even for moderate rotational velocities. Also, there<br/>is no observable parameter which is not affected by rotation. The problem gets<br/>further confounded by the fact that only V sin. i is observable and there appears<br/>to be no way of determinging l' and i independantly.<br/>We decided therefore to take an approach that would take care of most of<br/>these complications. We eliminated, in each duster, known Be stars, double-lined<br/>binaries and dose visual binaries with Δm<2.0 magnitudes. Only luminosity<br/>dass IV and V stars are considered. Differences between duster and duster would<br/>also not affect the final results as each cluster is analyzed independently . B and<br/>A spectral type stars were analysed independently. For each cluster, two colour<br/>indices were plotted against each other second order polynomial fit was<br/>derived. The observed minus computed (O-C) residuals in each index was determined<br/>and plotted against. Vsin i. These rotation effects determined are relative<br/>a:o both indices are affected by rotation. As interstellar extinction also reddens the stars, the Alpha Persei Cluster<br/>was analysed using both observed and dereddened indices. It, was found that<br/>for Alpha Persei, where non-uniformity of extinction is not large, both reddened<br/>and dereddened indices lead to similar results. However, as suggested by Gray and<br/>Garrison, we used the observed indices for other clusters as dereddening procedures<br/>for A-stars are based on an assumed calibration which may be in error due to<br/>rotational reddening.<br/>Evolutionary effects will introduce a scatter if the cluster members are not<br/>coeval. This is evident from our results for the Scorpio-Centaurus association.<br/>Here the Upper Scorpius members which are younger than the Lower Centaurus<br/>and Upper Centaurus subgroups were found to be separated in all diagrams of<br/>colour excess due to reddening versus V sin i diagrams. Also the scatter for Upper<br/>Scorpius was large where the interstellar extinction is highly non-uniform. The<br/>Upper Centaurus and Lower Centaurus group which are unreddened, consisting<br/>mostly of B2 and B3 type-stars show the reddening effect due to rotation in perfect<br/>agreement with theoretical predictions by Collins & Sonneborn (1977) for stars in<br/>the similar mass range.<br/>We have established firmly the rotation effects for various mass ranges by<br/>analysing a large number of clusters for which sufficient data. was available. As<br/>the predicted effects are a function of the mass, we analysed all clusters grouping<br/>them into three mass ranges corresponding to the spectral type ranges BO-B3, B5-<br/>B9 and A3-FO. The predicted indices for these ranges by Collins and his co-workers<br/>were analysed the same way as we did our observational data,.<br/>In our analysis of the theoretically derived indices we did not assume any<br/>distribution in V or i. Instead, for each value of i (30 0 , 45°, 60° and 90 0 ) we<br/>took sixteen values corresponding to w=O.2, 0.5, 0.8 and 0.9 for the mass range<br/>corresponding to the spectral types from BO-B3, B5-B9 and A3-FO and derived<br/>the rotation effects in different planes (such as ß, Cl; ß (u-b) etc.). We found<br/>that the rotation effects determined from observed data points for clusters, very<br/>closely matched the predictions for the various mass ranges. When this work<br/>was almost completed, Collins, Truax & Cranmer (1991) published the results of<br/>extensive model atmosphere calculations applicahle to rotating early-type stars.<br/>These indices were also analysed the same way as we did f01' Collins and Sonneborn<br/>(1977) models. On an av('rage tll<' predicted theoretical rot.ation effects of the two<br/>models does not difFer apprcciahly. This work establishes very firmly, for t.he first.<br/>time, that. not only rotation effects can be discerned from observa.tions but. also<br/>that the agreement. is good with t,heoretical predictions of Collins & Sonneborn<br/>(1977) and Collins, Tmax & Cranmer (1991) for rigidly rotating stars.<br/>We derived ZRZAMS by two methods. In the first mf'thod we derived the ZRMS of each cluster using observed slopes of rotation effects. These were superposed<br/>to derive ZRZAMS. Similarly theoretical corrections for each star were made<br/>to derive ZRMS for each cluster. These were superposed to derive the ZRZAMS<br/>as derived from theoretical predictions (for i=600 ). The two sets were found to<br/>agree with each other. The absolute magnitudes were corrected only using theoretical<br/>predictions. The ß, Mv relation for ZRZAMS derived by us is in excellent<br/>agreement with the values for the lower envelope of B-stars in the ß, Mv plane<br/>derived by Crawford (1978). This is as expected since the slow rotators in such a<br/>plane would lie along the blue envelope. We have established for the first time the<br/>empirical zero rotation zero age values for the intermediate band indices u v b y<br/>and Hß.<br/>The most dramatic result tha.t we ha.ve obtained is tha.t the blue straggler<br/>phenomenon in young galactic clust.ers can be completely interpreted in terms of<br/>rotation effects in colour magnitude diagrams at least in the large majority of<br/>clusters with ages less than or equal to Hyades.<br/>The effect of rotation on observed colours of stars was considered as a possible<br/>cause for the observed position of blue stragglers in star clusters. We find that<br/>the observed blueness of the blue stragglers which are intrinsic slow rotators, in<br/>the B7-A2 type range can easily be accounted for by such effects. The reddening<br/>caused by rotation shifts the ent.ire cluster main sequence away from the zero<br/>rotation main sequence leaving the slow rota.tors behind. The rotation effect in<br/>(u - b)o index reaches a maximum in the B7 - AO spectra.l type range where all<br/>the slowly rotating blue stragglers are also concentrated. It is also therefore not<br/>surprising that the majority of these A-type stragglers are found to be CP stars.
650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM
Topical term or geographic name entry element Astronomy and Astrophysics Thesaurus
650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM
Topical term or geographic name entry element Stellar Interior
9 (RLIN) 12840
650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM
Topical term or geographic name entry element Stellar Rotation
9 (RLIN) 10198
700 ## - ADDED ENTRY--PERSONAL NAME
Personal name R. Rajmohan
Relator term Supervisor
9 (RLIN) 48851
856 ## - ELECTRONIC LOCATION AND ACCESS
Uniform Resource Identifier <a href="http://prints.iiap.res.in/handle/2248/133">http://prints.iiap.res.in/handle/2248/133</a>
Link text Click Here to Access eThesis
942 ## - ADDED ENTRY ELEMENTS (KOHA)
Koha item type Thesis & Dissertations
Source of classification or shelving scheme Universal Decimal Classification
Holdings
Withdrawn status Lost status Source of classification or shelving scheme Damaged status Not for loan Home library Current library Shelving location Date acquired Full call number Barcode Date last seen Price effective from Koha item type
    Universal Decimal Classification     IIA Library-Bangalore IIA Library-Bangalore General Stacks 27/07/1993 043:524.3-54/ MAT 11638 05/11/2021 27/07/1993 Thesis & Dissertations

Powered by Koha