UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Line intensities and special types in B type stars Maunsell, Charles Dudley 1947-12-31

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
[if-you-see-this-DO-NOT-CLICK]
UBC_1947_A8 M38 L5.pdf [ 3.33MB ]
[if-you-see-this-DO-NOT-CLICK]
Metadata
JSON: 1.0085372.json
JSON-LD: 1.0085372+ld.json
RDF/XML (Pretty): 1.0085372.xml
RDF/JSON: 1.0085372+rdf.json
Turtle: 1.0085372+rdf-turtle.txt
N-Triples: 1.0085372+rdf-ntriples.txt
Original Record: 1.0085372 +original-record.json
Full Text
1.0085372.txt
Citation
1.0085372.ris

Full Text

LINE INTENSITIES .AND SPECTRAL TYPES IN B TYPE STARS by Charles Dudley Maunsell A Thesis submitted in Partial Fulfilment of the Requirements for the Degree of • MASTER OF ARTS in the Department ' O f PHYSICS The University of British Columbia April, 1947 TABLE OF CONTENTS page General Spectral Classification - 1 Previous Investigations 3 Observational Material 5 Errors in Stellar Spectrophotometry 7 Measurements of Line Intensity .. 9 Spectral Classification 16 Luminosity Criteria 20 Classification of Stars 21 Concluding Remarks 24 Bibliography 27 TABLES • ' - page I Comparison of Measures from Good and Poor Plates 8 f II Stellar Data and Intensity Measures 12 III Intensity Measures from Photometric Atlas 15 17 Classification Ratios 19 V Spectral Types and Luminosities for Stars Measured 22 by Others . F L k ' I B S following page I Typical Spectra 5 II Rectified Line Profiles 6 III Intensity Measures 15 IF Classification C r i t e r i a 19 V Comparison of "Measured1' types with Previous . . Assignments 23 LIHS INTENSITIES AKD SPECTRAL TYPES IB" B TYPE STARS. by Charles Dudley Maunsell ABSTRACT Photometric measures of absorption l i n e i n t e n s i t i e s i n the spectra of f o r t y - f i v e B stars are given. The plates were taken and measurements made at the Dominion Astrophysi- c a l Observatory. Graphs have been prepared showing the inten s i t i e s plotted against the Henry Draper subtype of the star f o r the stronger l i n e s . Using these i n t e n s i t y measurements, those published by E. G. Williams, and unpublished measures by R. II. P e t r i e , c r i t e r i a for determining spectral type from r a t i o s of the i n t e n s i t i e s of the stronger l i n e s are sugges ted. Also, from the v a r i a t i o n of Balmer l i n e i n t e n s i t y with luminosity, a method of determining absolute magnitudes i s suggested. Spectral types and luminosities as determined from these c r i t e r i a are given f o r 133 B type stars for which photo metric measures of l i n e i n t e n s i t y are available. ACKNOWLEDGMENTS I would like to acknowledge the kind help of Dr. J. A. Pearce, Dominion Astrophysicist, and the other members of the staff of the Dominion Astrophysical Observatory, including Dr. C. S. Beals, now. Acting Dominion Astronomer, who a l l kindly contributed information and suggestions on the conduct of this investigation during my work at the Observatory. Especially I wish to thank Dr. R. M. Petrie, who supervised the work, for his many discussions of the problems involved, for the luminosity data he provided, and for permission to use his unpublished line intensity measurements. LINE INTENSITIES AND SPECTRAL TYPES IN B TYPE STARS The spectra of stars are c l a s s i f i e d according to their main absorption features. The spectral types are usually defined by the Harvard c r i t e r i a and are named 0 , B, A, E, G, K, M, R, N, S, with subdivisions numbered from 0 to 9 i a most types. These types depend chiefly on the degree of ionization in the s t e l l a r atmosphere and thus on i t s temperature. The degree of ionization i s indicated by the variation in intensity of the absorption lines in the spectrum. As the temperature of the stellar atmosphere increases certain lines increase i n intensity, reach a maximum, and then decrease. The temperature at which a line shows i t s maximum depends on the excitation potential of the lower level of the line and.the ionization potential of the atom or ion. These factors determine the relative number of atoms able to absorb the l i n e observed. This means that the atoms of high excitation and ionization potentials contribute most to the observed spectra of the hottest stars, while the lines of low excitation potential appear i n the Coolest stars. - 1 -2. In addition, in each type; a further classification can be made on the basis of absolute magnitude or intrinsic luminosity into giants, intermediates and dwarfs. This difference i n luminosity i s only partially due to difference in the stellar mass, while the chief cause i s that the giant stars have much more tenuous atmospheres than the dwarfs and thus a greater surface area. The pressure differences, which are equivalent to surface gravity differences, cause differences i n the absorption spectra of the stars. In giants the absorption lines are sharper and the inten s i t i e s of lines due to metallic ions are increased, while in dwarfs the lines are more diffuse and those due to hydrogen and helium are much broadened due to Stark effect. However, not a l l cases of diffuse lines in s t e l l a r spectra are due to luminosity effects, since high rotational velocities of stars tend to produce dish-shaped line profiles as a result of the integrated Doppler shift over the stellar disk. An examination of a st e l l a r spectrum as discussed above w i l l give the temperature and surface gravity to classify the star in a two parameter system. However, there is also certain evidence to indicate that this is not sufficient definitely to characterize a st e l l a r atmos phere. For example, among the hottest (Wolf-Rayet) and the coolest stars there appear differences that can hardly be explained except as variations in the abundance of various elements. Among the hottest stars are those of spectral types G and B. They are comparatively rare, -but owing to their great luminosity (a consequence of their high temperature) they can be seen for large distan ces in the galaxy. For this reason a knowledge of their motions proves useful in a study of the structure of the galaxy. For this to be of much value a knowledge of their distances i s required. These distances can 3 . be obtained i f both the apparent and real magnitudes of the stars are known. To obtain c r i t e r i a for determining spectral types and these absolute magnitudes was the object of the research upon which this thesis i s based. PREVIOUS INVESTIGATIONS The Harvard classification i s based on visual examination of low dispersion objective prism plates. Most of the revised classificaticns from various observatories such as Mount Wilson, Victoria, and the recent work of Morgan, Keenan, and Kellman 1 at Yerkes are also based on visual examination but of higher dispersion plates. Of these, the Victoria revised classification was made by J. A. Pearce largely on plates with a dispersion of 30 Angstroms/mm. at H^, while that at Yerkes 2 was made with dispersion 125 A/mm., at HY . E. 6. Williams, using plates taken at Mount Wilson, obtained line intensities from spectrpphotometrie measures for 0 and B type stars. These measurements by Williams comprise about the only extensive l i s t of measured line intensities i n the B type stars. In addition, there are measurements of absorption lin e intensity for several stars made by Rudnick^ using a wide-slit photometer method. The application of this method w i l l be discussed b r i e f l y later. There 1. Morgan, Keenan and Kellman, An Outline of Spectral Classification. 2 . E. G. Williams, Ap_." J., 83_, 279, 1936. 3 . Paul Rudnick, Ag. J., 83_, 439, 1936. 4. have also been several l i s t s of hydrogen line intensities published and a few special studies of special stars. These have not been referred to further in this discussion owing to lack of information about systematic differences i n measurement between such values and those made at the Dominion Astrophyslcal Observatory. Williams 1 used the line intensities obtained in his investiga tion to set up a classification scheme based on measured line intensities. 2 However, as discussed by Petrie i n his investigation of the 0 type stars, Williams' c r i t e r i a are based largely on lines of low intensity which are subject to large errors of measurement on low dispersion spectra. Since for a study of the fainter and more distant stars i t i s necessary to use low dispersion spectra and consequently spectra in which the weaker lines are obliterated, c r i t e r i a based on the most intense lines i n the i spectra have to be determined. This i s also required by the fact that many of these early type stars have shallow diffuse lines, increasing the d i f f i c u l t i e s of measurement. In B type stars by far the, most intense lines are those of the Balmer series of hydrogen followed by the lines of the diffuse singlet and t r i p l e t series of helium and the l i n e of ionized magnesium at A 4481. However, i t is well known thatJboth hydrogen (chiefly in later subtypes) and helium (especially i n early- subtypes) are enhanced in intensity i n dwarf and intermediate stars due to Stark effect caused by intermolecular electric f i e l d s , while the Mg II line i s enhanced in the giants. These facts make, i t undesirable to use the absolute intensities of any of the measured lines for c r i t e r i a . This • i s discussed by Williams 1, who comes to the conclusion that ratios of 1. E. a. Williams, A£.J_., 83_, 305, 1936. 2. B. M. Petrie, J. R. A. S. C., .38,, 337, 1944. 5 line intensities give the best guide to average characteristics. 0BSER7ATI0NAL MATERIAL v The observational material for this program consisted of 82 . plates of 45 B type stars distributed among the Henry Draper catalogue ' ' B8,9 sub-types as: BO, 3 stars, Bl, 3 , B2,, 4 , B3, 12, B5^  9./B9, 5« All these plates were taken with the 73 inch telescope of the Dominion Astrophysical Observatory by various members of the staff. The majority of the plates were taken using the 1M spectrograph (i.e. the spectrograph was used in the one prism form and the medium focal length camera) with a dispersion of 30 Angstroms/mm. at H ^ , although a few were taken with higher dispersion. Some typical spectra are shown in plate I. On each plate a calibration was impressed in order to be able to determine the characteristic curve of the emulsion used. Most of the plates were calibrated by a calibrating spectrograph giving a series of * spectra of differing intensity. These intensity differences were obtained by use of a rotating step sector in front of the slit of the calibrating spectrograph. The majority of the plates used had the ratio of the intensity of successive steps such that the common logarithm of the ratio was 0.2, but for a few of the older plates the logarithm of the ratio was 0.3 (i.e. intensity ratio 2:1). Both of these enable separate calibration curves to be drawn at different wavelengths so that each section of the spectrum is reduced by use of the correct calibration curve for that section. To determine wavelengths in the calibration a PLATE I Typical Spectra f o l l o w ] 6. mercury arc i s photographed with the calibrating spectrograph so that i t s spectrum appears next to the calibration. For most reductions i n this work the calibration curve for A 4047 was used for the portion of the spectrum between 43933 and- X 4144 and the calibration curve for A 4358 for wavelengths between A 4267 and A 4575* A few of the oldest plates had been calibrated with a tube sensitometer illumened by white ligh t with a f i l t e r . This impressed small spots of varying density on the plate. From this type of calibration only one mean calibration curve for a l l wave lengths on the plate could be obtained. To obtain the equivalent widths of the lines measured, the usual practice of the observatory was used. This consists of f i r s t running the plates through the microphotometer described by Beals.* To transform the microphotometer record to a true intensity record, the 2 semi-automatic intensitometer also described by Beals was used. Most of the records were reduced in two stages, the galvanometer deflection being f i r s t reduced to a "log intensity" scale and on this the line of the continuous spectrum was drawn. The second stage consisted of transforming the "log intensity" to a true intensity curve, keeping the continuous spectrum at a height of 10 inches on the paper. The six Pleiades stars were measured later and reduced in only one stage directly to the true intensity, but with varying height of the continuous spectrum. The intensity of the absorption lines was measured by drawing freehand a mean profile among the irregularities due to grain effect in the original plate as shown in Plate H. The area between this profile and the line of the continuous spectrum was measured with a planimeter. The planimeter readings were converted to the intensities of the lines I"! cTsT Beals, M. N., 96, 730, 1935. 2. C. S. Beals, J.R.A.S.C., _3j5, 44, 1944. 7. i n equivalent Angstroms, i.e. the width of the line of rectangular profile and depth equal to the height of the continuous spectrum which would absorb the same total amount of energy from the continuous spectrum as the actual line does. For lines in the wing of the hydrogen lines the residual intensity of the wing at the position of the line being measured was taken as the level of the continuous spectrum for this purpose. In addition to the intensity measures the apparent depth of the centre of the line profile was measured for the hydrogen and helium lines as a fraction of the height of the continuous spectrum. • ERRORS IN STELLAR SPECTROPHOTOMETRY Stellar spectrophotometry is not of extreme accuracy. The reasons for this l i e in the d i f f i c u l t i e s attendant upon the small lig h t intensity received from the stars. In order to obtain spectra with a reasonably short exposure only a short s l i t can be used in the st e l l a r spectrograph, since the stel l a r image, even with large telescopes; i s very small, about 0 . 4 mm. i n diameter. This allows only a small area of plate to be exposed and then be examined by the microphotometer. Thus the uncertaia- ties introduced by the random effect of plate graininess are of f a i r l y large magnitude. This effect causes uncertainties i n the position of the continuous spectrum and of the mean profile of the lines as drawn on the tracing. In spite of the small length of s l i t , with good seeing the stell a r image is too small to cover the whole s l i t length. In order to obtain even illumination of the s l i t this requires the guiding of the Rectified Line Profiles 8 telescope to be carried out so that the stellar image drifts along the length of the s l i t to expose each portion for the same time. If this has been imperfectly done, different portions along the s l i t of the spectrum will have been exposed to different positions of the characteristic curve .of the plate used, while the microphotometer records an average blacken ing of the spectrum. If the characteristic curve were perfectly straight this average would not affect the result, but i f the exposure of the weaker portion is such as to cause i t to l i e on the toe of the character istic curve a considerable error occurs. Table I illustrates the differences in readings of equivalent width and depth obtained between an unevenly exposed plate and the mean of two properly exposed plates of the same star (£ Cassiopiae). Table I Line Hy Helium I Mgll - 4009 • 4026 4471 4481 •r w i D w D (. ¥ D ¥ ' D ¥ D ¥ Poor Plate ,7.0 j 0.75 8 . 5 0.75 ; 0.44 0 . 2 2 1.40 O.46 2.14 0.57 0.71 Good Plates • 5 . 8 ' i i i 0.62 5.8 0 . 6 8 0,'442 0.16 1.03 a 38 0.9C 0 . 3 3 0 . 3 3 I t ' This example is an extreme one, since the plate in error is very noticeably poorly exposed, but a small amount of the same effect must remain in the spectra measured although in a l l other cases apparently evenly exposed plates were used. On account of these almost irremediable errors in the spectro graphic process a variation of 10$ in the measurements obtained is often 9. not considered extreme. In the measurement of the B type stars even larger errors are not surprising. One reason for this i s the fact that many of the lines are extremely diffuse and hence their measured intensit ies w i l l be very sensitive to errors i n drawing both the level of the continuous spectrum and the mean profile.• In later type stars, where the lines are deep and narrow, a small error i n height on the tracing w i l l produce only a small error i n the measured area, while a small error i n the case of a shallow diffuse line w i l l cause a large error in the measured area. MEASUREMENT OF LINE INTENSITIES Table II gives the measured line intensities i n equivalent Angstroms. For the Hydrogen lines and stronger Helium I lines the inten sity i s given in the column headed W, while that headed D gives the rel a  tive depth of the centre of the li n e . The intensities and depths as given are mean values i n the case where two plates were measured. The columns of the table give f i r s t the number the star i s given i n the Henry Draper Memorial Catalogue, followed by the constellation name. Then comes the visual apparent magnitude, while the next three columns give the spectral type, f i r s t as assigned at Harvard by Miss Cannon and li s t e d in the Henry Draper Catalogue, then the Victoria Revised type, as given by J. A. Pearce from visual estimates, 1 and lastly, types as determined from these measured intensities. The next two columns give the absolute 1^  Pub. D.A.O., vol. 5, No. 2 , 1931. 1 0 . magnitudes as determined from the measures and the number of plates of the star on which the measures are based, while the remaining columns give the actual measures. In the measures a dash (-) indicates that the line was not noticeable on the tracing, a question mark that the presence of a slight absorption i s doubtful, while a blank means, in general, that no detailed examination has been made. In the case of line depths, the blank means that, although an intensity has been measured, the lin e i s so diffuse and shallow that the depth observed i s unreliable. The note 2sp indicates that the star i s a spectroscopic binary with two similar spectra v i s i b l e . In this case, unless the two spectra coincide, the depth measurement has no meaning. In Table III are given line intensities of | 4 0 r i o n i s , B:8, 0( Lyrae, AO, and o< Cygni, A2 , as determined by measuring with the plani meter the profiles published by ?filliams and Hiltner.* The two A type stars were measured to see that the c r i t e r i a obtained would not be incon sistent with a smooth junction with the A type stars. In addition to the stars measured in this program, there have also been used i n the discussion of results, measurements for 27 B stars made by R. M. Petrie, partly for this program and partly i n his work on binary stars. These measurements are mainly unpublished. The measure ments given by Williams^ for 64 stars have also been, used, since a comparison of measures by the different measurers, as plotted in Plate III, f i g . 1, indicate no serious systematic differences. The values of line intensities i n equivalent Angstroms from these three sources have been plotted against the Henry Draper subtype for H, Hel, Mgll, and CII i n Plate III, f i g s . 2 , 3 , 5, 6 . For hydrogen in f i g . 2 the mean of H Y and H/ has been plotted, for neutral helium 1. W. A. Hiltner and R.C. Williams, Photometric Atlas of Stellar Spectra. 2 . E. G. Williams, Ap. J., 8J3, 279, 1936. 11 the mean of the four lines A 4 0 2 6 , ^ 4471 (diffuse t r i p l e t s ) , \ 4388, and A4144 (diffuse singlets), for ionized magnesium the line A.4481, and for ionized carbon the line \ 1+267 has been plotted. In f i g . 4 the ratio of the sum of the intensities of the two singlet lines to the sum of the intensities of the two tr i p l e t lines has been shown. Subtypes 4 , 6 , and 7 are missing from a l l graphs because they are not used in the Henry Draper classification. The very large scatter shown i n a l l graphs i s partly due to poor classification. This portion should be removed by the use of a classification scheme based on measured line intensities. This w i l l not remove a l l the scatter apparent on the diagrams, since there are varia tions in intensity i n each subtype, due to luminosity effects, variations due to errors i n measurement, especially of weak lines, and probably also variations due to other natural differences between the individual stars. 12. TABLE I I - STELLAR DATA Henry- Draper Number Name Appt. Mag.. . Spectral 1 Meas'd Abs. Mag. Plates ED Vict. Revd. MeasM 9531 Boss 340 5-77 B9 B8 +2.3 2 10516 f Persei 4.19 BOp BOne - - 2 11415 S Cassiopiae 3-44 B3 B5s B3.5 - 1 . 3 2 17573 41 Arietis 3 . 6 8 B8 - B7-5 +1.1 2 20315 30 Persei 5.38 B5 B7n B6 +1.6 2 20319 6 . 0 2 B9 - B7 +1.4 1 20365 29 Persei 5 .30 B3 B3 B3 -0.1 1 20418 31 Persei 5.08 B3 B3 B4 -1.2 1 20809 Boss 767 5.30 • B3 B3 B4 - 1 . 3 1 21362 Boss 783 5.64 B5 B8nn B5 -1.8 1 21428 34 Persei 4.67 B5 B5 1 B3 .5 -0.3 2 23180 0 Persei 3.94 Bl B2k BO.5 -2.8 2 23324 Boss 855 5.63 B8 . - B7 +0.5 2 23432 Boss 8 6 l 5-85 B8 - B7 +1.7 2 23441 +24°556 6 .46 B9 - B9 +2.2 2 23753 Boss 872 5.51 B8 - B7.5 +0.3 2 23850 Boss 877 v 3.80 BS - B7 -0.7 2 23950 5.92 ' B9 - B 9 . 5 +1.1 2 25940 48 Persei 4 . 0 3 B3P B3e B3 -2.2 1 29763 f Tauri 4 . 3 3 B5 B5n B3.5 +0.9 1 30836 irh- Orionis 3-78 B3 B2s B2 -3.0 2 31237 77-5 Orionis 3-87 B3 B2s Bl -2.8 2 33328 X Eridani 4 . 3 4 B2 B3nk Bl -2.1 2 35039 22 Orionis 4.65 B3 B3ns B1.5 - 1 . 5 2 35411 7[ Orionis A 3.44 Bl BOk Bl -1.8 2 35468 X Orionis 1.70 B2 jB2s B2 -2.0 2 35715 Orionis 4 . 6 6 B2 B2 Bl -1 .7 2 36267 A Orionis 4 . 3 2 B3 B4n B5 +0.1 2 36822 ^'Orionis 4 . 5 3 BO BOssk BO. 5 -2.6 2 37742 y Orionis br 2 .05 BO BOnk BO -4.7' 2 37756 Boss 1399 1 5.00 B3 33 Bl - 1 . 6 1 42560 £ Orionis 4.35 B3 B3nn B3 -0.5 2 45542 -p" Geminorum 4 . 0 6 B5 B5ne B5 -1 .1 2 58715 P Canis Min. 3 . 0 9 B8 - B8 -0.4 2 109387 x Draconis 3.88 B5P B5e B5 -2.0 2 116658 <*Virginis 1.21 c B2 B2 B2 -2.9 2 144217 B' Scorpii 2 .90 Bl B2k B2.5 -2.0 2 149212 15 Draconis 4 . 9 8 B8 - B 9 . 5 +2.9 2 155763 if Draconis 3.22 B5 B8s B 7 . 5 -2.3 2 177756 \ Aquilae 3.55 B9 - B9-5 +1.9 2 180554 1 Vulpeculae 4.60 B5 B5n B3-5 - 1 .5 2 196867 << Delpnini 3 .86 B8 - BS +1.3 2 198667 5 Aquarii 5.50 BS . - B9.5 +0.1 . 2 202904 V Cygni 4.42 33P B3nek B2 -1.5 2 212120 2 Lacertae 466 B5 B5 B4.5 -0.8 2 1 3 . TABLE II (Cont'd) INTENSITY MEASURES H.D. No, Hydrogen • . Helium I . y ( 4 3 4 0 ) i (4101) 4471 4026 4388 4144 w D ¥ D w D ¥ D ¥ D ¥ D 9531 12.00 .71 11.28 .72 0 . 5 2 . 1 0 0 .38 .12 0 .34 . 0 6 0 .12 10516 em em - 0 . 7 5 0 .74 - - 0 . 8 4 11415 5 - 8 4 . 6 8 5.80 .62 0 . 9 0 . 3 3 1 .08 • 38 0 .66 . 2 4 0 .50 • 23 17573 1 0 . 4 4 . 6 5 1 0 . 0 6 . 6 8 0 . 4 1 . 1 0 0 .49 .12 0.22 . 0 7 0 .10 20315 9 . 2 9 . 6 2 9 - 1 5 . 6 4 0 .66 .10 0 .60 .12 0 .48 0.18 20319 9 . 8 0 .72 11.20 • 70 0 . 5 0 .11 0 .48 .10 0 .23 0 .25 .08 20365 6 . 4 4 . 5 9 5.88 . 6 0 1 .15 . 2 6 1 .14 • 31 0 .74 . 2 0 0 .48 .15 20418 6 . 1 9 •.50 6 . 6 4 .51 1 .02 .17 1 .24 . 2 1 0 .64 .10 0.70 .13 20809 6 . 5 2 . 5 4 6 . 0 8 • 56 0 .92 .18 0 .97 . 2 6 0 .46 . 0 9 0 .35 . 0 9 21362 7 .02 • 51 6 . 6 2 • 53 0 .69 .13 O.58 .11 0 .41 .08 0 .42 . 0 8 21428 6 . 8 9 . 6 0 6. 60 . 6 1 1 .04 . 2 4 1 .20 . 3 2 0 .68 . 1 4 0 .60 .18 23180 3 . 4 9 • 52 2 .73 . 5 0 1 .07 ' • 36 1 .03 • 41 0 .66 • 30 0 .48 .24 23324 9 . 5 8 . 6 2 9 . 7 8 . 6 4 0 .41 . 0 9 0 .50 .11 0.28 . 0 6 0.17 . 0 5 23432 11.38 .70 1 0 . 4 4 . 7 1 0 .57 .10 0 .59 .15 0 .42 . 0 8 0.15 . 0 6 23441 11.52 . 6 6 I I . 6 9 - • 71 0 .21 . 0 5 0 .27 . 0 7 0 .14 . 0 4 0 . 0 6 23753 9 . 4 6 .59 8 . 9 8 .61 0 .36 . 0 6 0 .42 .10 0 .32 . 0 7 0 .09 .04 23850 8 . 2 5 .62 7 . 8 5 . 6 2 0 . 3 4 . 0 7 0.53 .10 0 .33 . 0 5 0 .14 . 0 4 23950 1 0 . 6 2 •75 9 . 7 0 .72 0.21 .08 0 .34 .10 ? 25940 4 . 7 7 em 5 . 1 6 em 0 .86 .19 1.00 . 2 4 0.75 .18 0 .44 .12 29763 8 . 4 0 .61 7.80 . 6 3 1 .64 . 3 0 1 . 3 3 . 3 2 0.72 .19 0 .64 .17 30836 3 . 9 2 • 54 3 . 5 9 • 56 1.13 • 37 1.00 . 4 2 0 . 6 l .30 0 .53 . 2 7 31237 3 . 9 6 . 5 2 3 . 1 9 .48 1.18 . 3 6 0 . 9 4 . 3 4 O . 6 3 . 2 9 O.63 . 2 4 33328 4 . 3 4 • 37 3 - 8 3 • 38 1.28 .18 1.19 . 2 0 0.81 .12 0 .55 .11 35039 4 . 9 2 . 6 4 4 . 6 6 .62 1 .50 . 4 8 1 . 2 5 . 5 0 0 .86 . 4 2 0 .98 • 41 35411 4 . 7 5 2 s p 3 - 8 5 1 .42 1.18 0 .74 0 .72 35468 4.88 . 5 2 4 . 3 8 . 5 2 1 .18 .36 1.21 . 4 3 0.75 • 30 0.80 . 3 3 35715 5 . 0 3 2 s p 4 . 0 6 1 .45 1 .18 0.97 0 . 4 9 36267 7 .66 . 6 0 7 .72 . 6 0 0 .89 .18 0 .86 .22 0.37 . 0 9 0.28 .08 36822 3 . 7 5 .50 2.77 . 4 6 1 .29 . 4 0 1 . 0 2 . 3 8 0.71 . 2 8 0 .32 .21 37742 1.74 . 3 8 1 .49 • 34 0.88 .26 0 .57 . 2 1 0 .30 .11 0 .20 . 0 7 37756 4 . 5 0 .51 4 . 5 1 .51 1 .43 . 3 5 1.31- • 39 O.76 . 2 6 0 .89 . 2 9 42560 6 . 6 4 .56 6 . 2 9 . 6 0 1.28 . 2 9 1 .24 . 3 0 0 .70 .18 0.67 .18 45542 7 .12 .55 6 . 2 6 . 5 8 0.82 .14 0.61 .16 0 .45 •07 0 .23 . 0 8 58715 9 . 2 0 .55 9 . 5 6 . 6 6 0 .43 . 0 8 0 .33 . 0 6 0 .26 0.10 . 0 6 109387 6 . 0 2 . 4 4 4 . 8 0 . 4 8 0 .70 .18 0 .41 .12 0 .46 • 13 0 .19 116658 4.28 2 s p 3 . 5 2 1.19 0.88 0 .68 0 .48 144217 4 . 3 5 2 s p 5 . 3 7 1.12 1 .02 O.76 0 .59 149212 II . 6 9 • 75 1 3 . 2 0 .78 0 .29 .08 0 .24 . 0 8 - 0 .07 155763 5 . 6 8 . 6 2 6 . 4 2 •70 0 .33 .17 0 .42 .21 0.14 . 0 9 0 .18 . 0 9 177756 1 0 . 7 9 . 6 6 11.36 .67 0 . 3 0 . 0 6 0.21 . 0 6 - 180554 5 . 7 6 . 5 6 • 5 . 6 7 .58 0 .84 .18 O.96 . 2 6 0.58 .12 0 .60 .15 196867 IO.46 . 6 8 10.28 .73 ' O.36 . 0 7 0 .30 . 0 7 0 .27 . 0 5 0 . 0 4 198667 9 . 3 2 . 7 4 8 . 9 6 .75 O.23 .13 0 .20 .11 0.12 0 .08 202904 5 . 0 5 • 38 5 . 0 2 •47 1 .25 . 2 6 1 .25 .28 0 .75 .19 0 .79 .19 212120 6 . 7 4 2 s p 6.80 0.77 0 .86 0 .39 0.47 14. TABLE II (Cont) INTENSITY MEASURES H.D. No. He I Mg I I C II Ca l l Si II S i IV 0 I I 4009 4121 4481 4267 3934 4128 4131 4089 4070 4072 4U7o (K) - 9531 0 .43 0 . 2 2 0.13 0 . 0 8 10516 .... - - - 11415 0.42 0 . 2 4 0 .33 0 .20 0 .26 0.09 0.10 17573 - - 0 . 2 9 0.11 0 . 0 4 0 . 0 8 20315 - 0.09 O.58 0.14 0.18 0.13 - 20319 • - ' - O.40 0.49 0.18 0.13 20365 0 . 4 4 0.14 0.31 0 .22 0 . 2 4 20418 0.21 0.25 0 .31 0.19 0.14 0.18 0.18 20809 •? ? 0.21 0.14 «? 21362 •> 0.12 flaw ?' 0 . 0 4 21428 0 . 4 8 0.29 0.31 0.18 0 . 2 2 2318O 0.45 0.41 0.18 0 . 2 3 0.10 0 . 0 4 0.11 .19 .13 .23 23324 - - 0 . 3 4 0.18 0.17 0.14 23432 - - 0.57 0.31 0.12 0 .14 2 3 4 U • - - 0.26 0.15 0.07 0.10 23753 - - 0.31 0 . 0 4 0 . 0 5 0.07 23850 •?' - 0.29 0.10 0.09 0.10 23950 - - O.36 0.29 0.19 0.14 25940 0.35 0.14 0.39 0.18 0.12 29763 0 .43 0.28 0.28 0.25 0.25 0 . 0 9 0.12 30836 O.60 0 . 3 3 0.31 0 . 2 4 .15 .10 .18 31237 0 .47 0 .40 0.29 0 . 3 4 0.19 0 . 0 4 0.06 0 . 0 6 .06 .07 .12 33328 O.48 0 . 3 0 0.22 0.13 0.13 .07 .08 .13 35039 0.57 0.47 0.32 0.29 0.19 .11 .08 .10, 35411 0.48 0.35 0 . 2 2 0 . 2 4 0.13 0.17 • f t 35468 0.57 0.40 0.32 0 . 2 8 0.11 :o7 .09 35715 0.53 0.37 0.15 0.08 0.18 47 36267 0.18 0 .22 O.26 0.13 0.12 0.14 0.11 36822 0.28 0.27 0 .20 0.12 0 . 2 4 0.37 .25 .16 .18 37742 0.07 0.17 - 0 . 0 6 0.13 0.55 37756 0.73 0 .40 0.39 0.14 0.08 .07 .06 .12 42560 0.49 0 .24 0 .33 0 . 2 4 0 . 2 0 45542 0 . 2 0 0 . 0 5 0 .44 ? 0.26 0 . 0 2 0 .07 58715 - - 0 . 4 2 - 0.14 0.14 0 .21 109387 0.16 0.08 O.29 0 . 0 5 0 . 0 4 0 . 0 3 116658 0.40 0.32 0 .26 0 . 0 3 0 . 0 4 •3? 144217 0.36 0 . 4 2 0.28 0 .25 0.10 .'07 . 0 6 " . 0 7 ' 149212 - - 0 . 5 4 0 . 5 8 0.14 0 .22 155763 0.21 0 .09 0.25 0 . 0 9 0.14 0.10 0.09 177756 - - 0.39 Q . l6 0 .09 0.08 180554 0.44 0.12 0 .38 0.18 0.21 0 . 0 4 0 . 0 6 196867 - - 0.41 0.42 0.12 0.11 198667 - - 0.39 0.32 0.18 0.12 202904 0.55 0 . 2 4 0 . 2 9 0.20 0.07 0 . 0 2 0 . 0 9 212120 .0.22 0.16 0 . 3 5 0 . 2 0 0.25 0.11 0 .14 TABLE II (Cont.) H.D.No. Si III SilV N i l NUT F e l l CII c m 4069 Hel He II • - 4553 4568 .4575 4116 3995 4097 4233 3920 3927 4200 4542 9531 0.12 10516 em 20319 0.12 2318O 0.03 30836 0.06 0.35 0.35 31237 0.43 0.37 0.22 0.20 0.45 33328 0.08 0.07 0.04 35039 0.20 0.12 mm 0.08 35411 0.18 0.07 - 0.13 0.11 35468 0.24 0.18 0.12 35715 0.04 0/08 36822 0.28 0.25 0.16 0.22 0.21 37742 0.28 0.1C 0.22 0.46 0.17 0.12 37756 0.20 144217 0.21 0.08 0.17- 0.05 ? 0.16 149212 177756 0.18 196867 0.08 TABLE III - MEASUREMENTS FROM TRACINGS IN ATLAS H.D. No. Name H.D. Type Appt. Mag. ^ E q u i v a l e n t Widths 1.4340 HY 4101 H S 4471 Hel 4026 Hel 4388 Hel 34085 172167 197345 /3 Orionis ^ Lyrae o(Cygni< B8p AO A2p 0.3 0.1 1.3 1.86 19.5 2.86 2.02 14.7 3.04 0.50 0.09 0.18 0.57 0.13 0.12 0.25 0.04 ' H.D. No. 4i44 Hel 4009 Hel 4121 Hel 4481 MgH. 3933 C a l l 4233 F e l l 4267 CII 4128 S i l l 4131 S i l l 34085 112167 197345 0.37 0.22 0.03 0.03 0.17 0.04 0.53 0.26 0.90 O.63 0.78 O.16 0.14 0.60 0.23 0.33 0.06 0.35 0.32 0.05 0.34 PLATE IE H.D. T y p e To follow page 15 1 6 . SPECTRAL CLASSIFICATION •| With the exception of the work of Williams 1, practically a l l classifications so far published of the B type stars are based on visual examination of plates of the ste l l a r spectrum. In this category, for example, f a l l the determinations of Miss Cannon for the Henry Draper catalogue which are based on the c r i t e r i a given i n the introduction to the catalogue 2, the Yictoria Revised classification, by J. A.. Pearo% using visual estimates of line intensity and based on c r i t e r i a as yet unpublished, a scheme given by E. G-. Williams and D. L. Edwards,^ and that given by Morgan, Eeenan, and Kellman.^ These visual estimation methods enable an experienced person to classify spectra rapidly and f a i r l y consistently. However, such methods do not guarantee absolute agreement between differ ent observers, even when using the same plates as Tables I and II given by 3 Williams and Edwards show. A more serious d i f f i c u l t y l i e s in the fact that an inexperienced observer cannot take the cla s s i f i c a t i o n c r i t e r i a given and expect to produce results agreeing with those obtained by those who l a i d down the c r i t e r i a . Other objections to the visual method are that i t i s almost impossible to use the same visual c r i t e r i a for plates of a l l dispersions, hence introducing inconsistencies, and that errors are introduced by the usual diffuse lines (often caused by rotational effects), by poor exposure, and by luminosity effects, since they cannot be visually estimated with precision. 1. E. G. Williams, Ap_. J., 83_, 305, 1936. 2 . Harvard Annals, 91 , Z, 1918. 3 . E. S. Williams ancT D. L. Edwards, M. N., 98 , 4 6 7 , 1938. 4 . Morgan, Keenan, Kellman, An Outline of Stellar Classification. 17. A classification scheme based on measured line intensities should be free from these disadvantages since i t i s based on objective measures of the line intensities, which should be the same for a l l observers, rather than on subjective estimation which w i l l certainly vary from observer to observer and probably from time to time for the same observer. The c r i t e r i a advanced by Williams 1 provide an objective scheme of this type, but, as discussed above, i t i s chiefly based on measurements of weak lines which are d i f f i c u l t to measure accurately on low dispersion spectra, especially.if the lines are at a l l diffuse in character. Theoretically a. classification scheme based on ratios of the intensities of lines due to the same element in different stages of ioniz- ation would give a good indication of temperature since i t should be independent of abundance effect. For example, since in B type spectra lines due to S i l l , SiIII, and SilV appear, i t should be possible to base a classification on the ratios S i l l / S i l l l and SiHI/SilV. However," this does not appear very practical since the lines are of low intensity, . and hence are unsuitable because of the effect of accidental errors i n . measurement. Another possible theoretical classification could be based on an 2 extension of the argument suggested by Goldberg for the ratio of the diffuse singlets to the diffuse t r i p l e t s of Hel. However, as shown in Plate HI, figure 4, the measured results show considerable variation i n this ratio within one spectral subtypej together with a f l a t maximum for the mean values in the early subtypes. Further consideration also shows that even on a theoretical basis curve of growth effects and the line 1. E. G. Williams, Ap_. J., 83_, 310, 1 9 3 ° . 2 . Leo Goldberg, Ap_. J., 89_, 623, 1939. 18. broadening due to Stark effect would complicate the ratio and prevent i t s practical use. The outstanding variation in B type spectra i s the increase in intensity of the lines of the Balmer series of hydrogen with decreasing temperature. The hydrogen lines also increase so much in intensity with decreasing luminosity that they can only be used for type c r i t e r i a i f the absolute magnitude is already reasonably well known. Hence i t appears that a practical scheme w i l l have to be based on ratios of.the lines of highest intensity, i.e. those of hydrogen, hel- ium, and ionized magnesium. The greatest change i n ratios between sub types occurs in the case where one member of the ratio i s increasing i n intensity with advancing type, while the second i s decreasing. Since the hydrogen and magnesium lines increase in intensity with decreasing tempera ture, while the helium lines f i r s t increase i n intensity, then reach a maximum and decrease, the, obvious ratios to try are those of hydrogen to helium and magnesium to helium. However, since both hydrogen and helium lines are enhanced in dwarfs, although hydrogen to a greater extent, while the magnesium line i s enhanced in the giants, i t i s obvious that one ratio w i l l not be suitable for a i l luminosity groups. Hence a f i n a l classification cannot be assigned u n t i l the luminosity has been determined, Similarly to obtain the correct luminosity a knowledge of the spectral type is required (see next section). However, the criteriaare such that a successive approximation method w i l l work to give both spectral type and luminosity. Hence an assumption of a prelimim ry type or luminosity (by visual examination of the spectrum or otherwise) enables a f i n a l determination to be reached f a i r l y rapidly. The ratios suggested as suitable for type c r i t e r i a are given 19 in Table I? and plotted in Plate IV, figures 7 and 8. The ratio H/Hel is the ratio of the mean intensity in equivalent Angstroms of and K$ to the mean intensity of the Hel lines A4471, A4026, \h3&8, and A 4144. The ratio Mgll/Hel is the ratio of the Mgll li n e \448l to the mean of the four Hel lines. The H/Hel ratio was given greater weight in the early subtypes where the Mgll line i s weak. The line depths measured along with the intensities have not been used for classification purposes because of the fact that the recor ded effect i s not due wholly to the true line depth but is considerably modified by the spectrograph in redistributing the light in the spectrum by diffraction effects. This varies with the spectrograph used so that c r i t e r i a including such material could not be used on spectra taken with a variety of spectrographs with different dispersions. TABEE IV - SUGGESTED TYPE CRITERIA Ratio H/Hel Ratio Mgll/Hel Type Giants Intermediates Dwarfs Giants Intermediates . and Dwarfs BO 2.0 3.6 • 3.6 0.44 0.10 Bl 2.4 4.. 4 4.4 0.48 0.16 B2 2.8 5.0 • . 5.0 0.52 0.22 B3 3-4 6.0 r 6.6 0.58 0.30 B4 4.0 8.6 9-8. 0.64 0.44 B5 4.4 12.0 13.6 0.74 0.62 B6 4.8 16 19 0.92 • . 0.86 B7 5.6 21 26 1.2 1.12 B8 6.4 26 36 1.6 1.4 B9 8.0 40 60 3.0 ' 2 . 0 e o r 3 0 2 0 '0 PL AT EE? Fig. 7 Classification fatfo I - yjfe. A Giants B Inter mediates C Dwarfs gio il 'i2. i3 <f iS" i 6 - i7 ,8 glflio ,1 ,2 • 3 A ,5 ,6 ,7 ,8 ,3 Fig. 8 C l a s s i f i c^t ior , R a t i o IE -jgf 10 J I I Absolute Magnitude _j l i i i L J L -+ To f o l l o w -oage 19 2 0 . LUMINOSITY CRITERIA The main effect of luminosity apparent in a B type s t e l l a r spectrum is the very large increase i n the strength of the hydrogen lines due to Stark effect. To enable luminosities to be determined from the measurements of this program i t was necessary that the stars originally used have known absolute magnitudes. As the results obtained are to be used to study galactic structure, i t is desirable to use distance c r i t e r i a obtained independently of consideration of galactic structure. The absol- 1 ute magnitude c r i t e r i a used by Williams were based on distances determined by measurement of the intensity of the K lines due to interstellar calcium, which in turn he calibrated against distances determined from galactic motions. Tne stars chosen for this program were largely those whose dis tances were known from non-spectroscopic c r i t e r i a . These included stars with known trigonometric parallaxes of greater than 0" .010 and other stars whose parallax could be computed from group or cluster motions. For most of the stars used Dr. R. M. Petrie computed absolute magnitudes from this data and in a few cases gave the magnitude as determined from 2 the K line intensity by using the relationship given by Evans. For the six Pleiades stars the absolute magnitudes were kindly calculated by 3 Dr. J. A. Pearce, using the cluster parallax as calculated by him . The material used i s naturally rather weak in the giant stars, since they are. rarer and on the average are at a much greater distance and hence there are very few i n the region close to the sun to which the 1. E.G. Williams, Jp_. J., 83_, 326, 1936. 2 . J. W.-Evans, Ap_. J., 275, 1941. 3 . J.A. Pearce, JRASC.40, 143,1946. 2 1 . choice of stars with relatively large trigonometric parallax restricts the distance. x By using the absolute magnitudes as obtained above a plot (Plate IV, figure 9) of total absorption of the hydrogen lines against absolute magnitude was made. Tnis was used to evaluate the"measured" luminosities given. CLASSIFICATION OF STARS The system of classification as developed above has been . applied to the stars measured, the results being included in Table I I , and to the stars measured by Williams and by Petrie, for which the results are given in Table V. This table i s arranged similarly to the f i r s t columns of Table I I . In the last column of Table V i s indicated by a W or a P whether the intensities used were measured by Williams^" or by Petrie. 2 The correlation between the measured type and the H.D. type and that between the measured type and the Victoria Revised type are shown in Plate V. The general tendency seems to be for the measured type to be somewhat earlier than the visual estimates. This i s reasonable, since the frequent diffuseness of the lines, tending to obliterate the weak lines, makes the spectrum appear later on visual examination. 1. E. G. Williams, Ap. J., 8%, 2 ? 9 , 1936. 2'. R. M. Petrie, unpublished. 22. TABLE V - TYPES FOR STARS MEASURED BY OTHERS. H.D. . No. . Name Appt. Mag; . Spectral Type Meas'd Abs. Mag. Meas^  urer. H.D. Vict. Revd. Meas^ 358 o< Andromedae 2.15 AOp BS . -1.1 P 698 +57°28 7.08 B5 - B5 . 5 - 3 . 5 P 886 Y Pegasi 2.87 B2 . B2ss Bl - 2 . 0 W I 4 8 6 TV Cassiopeiae var B9 , - B8 +2.7 P 3360 J Cassiopeiae 3.72 B3 B2sk B2 - 2 . 0 w . 4180 0 Cassiopeiae 4.70 B2 B5n B3 . - 2 . 6 w 4727 •p Andromedae 4.42 B 3 B5s B4 0.0 - p ; 5394 y* Cassiopeiae 2.25 BOp BOnne BO. 5 w 13854 Boss 507 6.42 Blp BOsk BO - 4 . 0 . ¥ 14134 Boss 519 6.66 BO B2sk B2 - 5 . 5 W 21291 Boss 781 4.42 B9P - B9 - 5 . 3 ¥ 22928 b Persei 3.10 B5 . B8n B4.5 -1 .8 W 23480 Boss 865 4.25 B5 B7n B6 - 0 . 6 ¥ 24398 J Persei 2.91 Bl Bis B2 - 4 . 9 W 24534 X Persei var BOp BOnne BO - ¥ 24760f 6 Persei f 8.1 - B9 +6 ¥ 25833 •330785 6.61 B3 B3k B3 - 0 . 4 P 28446b 1 earn b ' 5.86 Bl B2nk Bo - 2 . 7 ¥ 28446f I Cam f 6.61 Bl BOsk BO. 5 -1 .8 W 29376 +70676 6 .89 B5 B5k B3 - l . l P 32343 Boss 1195 5.31 B3P B3e B3 - 1 . 8 W 32630 7\ Aurigae 3.28 B3 B3 B2.5 - 2 . 7 W 34085 (3 Orionis 0.34 B8p - B7 - 5 . 7 w 34333 (3 Tauri Bl ' - B2 - 2 . 7 . p 35497 1.78 BS - B5.5 -1.1 ¥ 36371 X Aurigae 4.88 Bl B3ss B2 - 5 . 4 ¥ 36862 X 1 Orionis f 5.56 0e5 Bisk •' BO - 0 . 1 ¥ 37128 £ Orionis 1.75 BO BOk BO.5 -5 .2 Iff 37202 J Tauri 3 .00 B3P B3e B3 +1.6 ¥ . 38771 ^ Orionis 2.20 BO BOk BO. 5 - 5 . 2 W 39698 Boss 1464 5.89 B2 B3 BO.5 -1 . 6 ¥ 40111 Boss 1475 4.90 B2 BO BO - 3 . 1 - ¥ 4 1 H 7 yc 2 orionis 4.71 B2p^ B2ssk ' BO - 6 . 3 ¥ 41534 Boss 1517 5.64 B3 B3 Bl +0.1 W 44701 r3° 1413 6.58 B5 B5n B3.5 - 0 . 8 P 44743 (#Canis Ma 1 .99 Bl Blss Bl - 3 - 8 ¥ 58050 +150 1564 6.37 B3 B3e B3 -1 . 7 W 74280 7\ Hydrae 4.32 B3 B5n B1.5 -1.5 ¥ 87737 7\Leonis 3-58 AOp . - B4 - 3 . 1 W 87.901 c< Leonis 1.34 B8. B6n B7 - 0 . 7 w 89688 Boss 2748 6.53 B3 B3 ' S B1.5 " -1.5 ¥ 91316 p. Leonis 3.85 BOp BOsk BO. 5 - 4 . 9 W 93521 +38° 2179 6.89 B3. B3nn BO - 2 . 4 ¥ L00600b 90 Leonis b 6 i 0 B3 . B3 B3 0.0. ¥ L00600f | 90 Leonis f 7 . 3 B3 fi5 B5 +0.1 ¥ 2 3 TABLE V (Cont.) TYPES FOR STARS MEASURED BY OTHERS H.D. No. Name Appt. Mag. Spectral Type Meas'd Abs... Mag. Meas urer H.D. Vict. Revd. Meas'd 120315 t\ Ursae Ma 1.91 B3 B3n B3 +0.7 ¥ 136175 U Coronae Bor var B8 B3 B5 +1.6 P 139892 & G C 7 3 5 2 b 5 . 0 7 B8 B8n B5.5 +2.7 P 147394 -fr Herculis 3 . 9 1 B5 B7s B3.5 +0.7 ¥ 148184 X Ophiuchi 4 . 8 5 B3 B3e BO -2.6 W 148479 cA Scorpii f 6 . 5 A 3 B2.5 +1 W 149438 V Scorpii 2.91 B0 Bis BO. 5 -2.2 ¥ 149757 H Ophiuchi 2.70 BO BOnnk B2 -4.2 W 149881 +14°3086 6 . 5 9 B2 B2k BO -3.2 W 156247 U Ophiuchi var BS • B5nk B3-5 -0.5 P 156633 A. Herculis var B3 B3 B3 -0.2 P 160762 1 Herculis 3 - 7 9 B3 B3s B3 - 3 . 6 w 162732 Boss 4514 6 . 4 3 BS - B9 0.0 ¥ 164353 Boss 4548 3 . 9 2 B5p B8s B6 - 5 . 0 ¥ 169454 6.8 BO B2 - 5 . 4 ¥ 175227 DI Herculis var A B5 B4 - 0 . 9 P 180939 RS Vulpeculae var B3 - B5 0.0 P 185507 C Aquijae 5.17 B3 B3 Bl -0.1 P 187811 Boss 5068 4 . 9 1 B3 B5ne B2.5 -1.1 ¥ 190603 Boss 515O 5 . 6 9 BO BOssk BO -5.8 W 190967 7 . 9 2 B3 BO - 3 . 3 P 192422 + 3 8 ° 3 9 5 6 7.10 B2 BOsk BO - 4 . 7 W 193536 +45 G 3139 6.28 Bl B2k Bl -1.2 P 194279 +4004150 7 . 0 5 BO BOsk BO - 5 . 5 ¥ 197911 7 . 9 B5 - B2.5. -3.0 • P 198478 Boss 536I 4 . 8 9 B2 B2sk Bl - 5 . 9 ¥ 198846 Y Cygni var B2 08nnk Bl ' -3.2 P 199081 Boss 5375 4 . 6 8 B3 B3k B3 +1.3 P 199140 + 2 7 o 3 9 0 9 6 . 4 4 B3 Bis B2.5 -4.0 P 200120 Boss 5410 4 . 8 6 BOp B3nne B3 -0.4 ¥ 204172 Boss 5512 5 - 8 4 BO BOk. BO -4.0 ¥ 205021 fl Cephei 3 . 3 2 Bl Bl BO. 5 -1.6 ¥ 206165 Boss 5563 4 . 8 7 B2p B2sk B1.5 - 5 . 3 208185 +62°1992 7 - 7 B3 - Bl -0.2 ¥ 208392 +6102216 7.10 B 3 B3nnk Bl -1.5 ¥ 208947 +6501691 6.28 B3 B3k Bl +0.8 212455 + 5 5 ° 2 7 5 6 8 . 4 B2 - B3-5 -5.0 Iff 212571 7T Aquarii 4 . 6 4 Blp Blnnek Bl - 3 . 9 ¥ 213420 Boss 5810 4 . 5 4 B3 B3k BO. 5 -1.6 ¥ 216014 + 6 4 ° 1 7 1 7 6 . 8 3 B3 BOk BO. 5 -1.1 P 218066 B5 . - B2 -2.1 P 221253 Boss 6046 4.N89 B3 B3k B2 0.0 P 224151 Boss 6 l 4 2 6 . 0 5 BO BOk BO.5 -3.8 ¥ 228911 B3 BO +0.5 P 24. CONCLUDING REMARKS The progress of this research has shown that satisfactory c r i t e r i a for determination of spectral types and luminosity from photo metrically measured line intensities can be obtained. The results above give suggested numerical values for these c r i t e r i a and record some types and luminosities determined by their use. Since the reduction and i measurements for thirty-nine of the forty-five stars for which line inten sities are given took the greatest part of a four-month summer assistant- ship at the Dominion Astrophysical Observatory, i t i s obvious that, unless a more rapid method of obtaining intensities can be found, an application of this method to any large body of material would prove impracticable because of the time involved. However, a considerable increase in speed can be obtained by restricting the spectral regions measured to the lines being used for classification. A further saving of time can be made by reducing the microphotometer tracings to true intensity records by only one stage instead of the two stages used for most of this material. Owing to the relatively large probability of error in the measurements from a single plate i t i s not advisable to measure only one plate of a star, but a system by which only four lines i n each stellar spectrum are measur ed should prove about as satisfactory, as the system here suggested. The four lines suitable for this purpose are Hy at 4340, the Hel diffuse singlet at A4388, the Hel diffuse t r i p l e t at ^4471, and the Mgll line at A 4481. These have the advantage that they a l l l i e in a short region of 25. the spectrum, and hence one calibration curve w i l l prove sufficient to reduce the microphotometer record for a l l the lines. Use of this scheme would make very l i t t l e change in the intensity ratios for spectral type since in general the two hydrogen lines are of approximately equal inten sity and similarly for the two helium singlets and the two triple t s . Since the process of reduction of intensity records i s so time-consuming i t i s natural to consider the possibility of taking read ings of line intensiti es directly from the plate as was done by Rudnick."'" This method consists of using a photometer with a wide s l i t so that the complete width of the line being examined f a l l s inside the s l i t . The galvanometer deflection caused by the amount of light f a l l i n g on the sensitive element of the photometer can be read visually and by the use of suitable calibration the equivalent widths can be determined directly. The d i f f i c u l t i e s in this method l i e in the large variation in width of the spectral lines being measured, the relatively small depths of many of them, and the fact that the reading obtained i s not directly proportional to the equivalent width and behaves in such a manner that the difference from proportionality varies with the shape of the li n e . It i s obvious that the relative effect produced by an absorption line of given equivalent width i s approximately inversely proportional to the effective width of the analyzing s l i t of the photometer. Thus in a spectrum with sharp lines, a comparatively narrow s l i t can be used and the light transmitted through the photographic plate w i l l be significantly more than that through a similar length of the continuous spectrum. Hence an accurate reading can easily be obtained. However, because of the large number of diffuse l i n e stars, the minimum width of the analyzing s l i t w i l l be that which TI Paul Rudnick, Aj>. J., 83_, 439, 1936. 26. w i l l include a 10 Angstrom length of the spectrum. If the maximum depth of the center of the line i s only about 5% of the continuous spectrum as i n the case of many of the lines measured, the change between the absorption by the portion of the plate including the line and that of a portion including only continuous spectrum w i l l be very small, of the order of 2 or 3%« Since the errors inherent in the method (plate grain, etc.) w i l l be related to the tcbal amount of light transmitted by the plate while the reading desired w i l l be the difference between two such quantities, the result w i l l have a considerable probability of error. This does not exhaust the d i f f i c u l t i e s of this method, since to include the total width of the hydrogen lines (including the wings due to Stark effect) would require about 50 or 60 Angstroms of spectrum to be examined at once. For these reasons i t seems that the most practical system for obtaining line intensities for classification purposes i s that described above, using only four lines and making reductions i n only one step. BIBLIOGRAPHY Beals, C. s., M. N., ^6, 730, 1935-. J. R. A. s. c., 38, 44, 1944. Cannon, Miss A., Harvard Annals, 91, 1, 1918. Evans, J. W., Ap. J. ,__93_, 275, 1941. Goldberg, Leo, Ap.J., §2, 623, 1939. Hiltner, W. A., and Williams, R. C., Photometric Atlas of Stellar Spectra, Ann Arbor,1946. Morgan, W. W., Keenan, P. C. and Kellman, H., An Outline of Stella r Classification, i n An Atlas of Stellar Spectra, Chicag 1943. Pearce, J. A., Pub. D.A.0.,_5_, No. 2, 1931. J.R.A.S.C., 40, 139, 1946. Petrie, R. M., J.R.A.S.C., ^8, 337, 1944. Rudnick, Paul, Ap. J., 83_, 439, 1936. Williams, E. G., Ap.J., 8_2, 279, 1936. Ap.J., 83_, 305, 1936. Williams, E. G. and Edwards, D. L., M.N., 98, 467, 1938. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Country Views Downloads
China 11 3
United States 9 0
Belgium 3 0
Spain 2 0
Austria 1 0
Thailand 1 0
City Views Downloads
Shenzhen 9 3
Ashburn 7 0
Leuven 3 0
Beijing 2 0
Madrid 2 0
Unknown 1 15
Vienna 1 0
Redmond 1 0
Mountain View 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}
Download Stats

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0085372/manifest

Comment

Related Items