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

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LINE INTENSITIES .AND SPECTRAL TYPES IN B TYPE STARS  by  Charles Dudley Maunsell  A Thesis submitted i n P a r t i a l Fulfilment of the Requirements f o r the Degree of • MASTER OF ARTS i n the Department '  O  f  PHYSICS  The U n i v e r s i t y of B r i t i s h Columbia A p r i l , 1947  TABLE OF CONTENTS page General Spectral C l a s s i f i c a t i o n  1  -  Previous Investigations  3  Observational Material  5  E r r o r s i n S t e l l a r Spectrophotometry  7  Measurements of Line Intensity  ..  9  Spectral C l a s s i f i c a t i o n  16  Luminosity C r i t e r i a  20  C l a s s i f i c a t i o n of Stars  21  Concluding Remarks  24  Bibliography  27  TABLES  f  I  • ' Comparison of Measures from Good and Poor Plates  II  S t e l l a r Data and Intensity Measures  page 8 12  I I I Intensity Measures from Photometric Atlas  15  17  C l a s s i f i c a t i o n Ratios  19  V  Spectral Types and Luminosities by Others F L k  '  22  f o r Stars Measured .  I B S  following page  I  Typical Spectra  5  II  R e c t i f i e d Line P r o f i l e s  6  III Intensity Measures  15  IF  19  V  Classification Criteria Comparison of "Measured ' types with Previous . 1  .  Assignments  23  LIHS INTENSITIES AKD  SPECTRAL TYPES IB" B TYPE STARS.  by C h a r l e s Dudley  Maunsell  ABSTRACT Photometric measures of a b s o r p t i o n l i n e i n the s p e c t r a of f o r t y - f i v e B s t a r s are g i v e n .  intensities The  plates  were taken and measurements made at the Dominion A s t r o p h y s i c a l Observatory.  Graphs have been prepared showing the  s i t i e s p l o t t e d a g a i n s t the Henry Draper f o r the stronger l i n e s .  subtype  inten-  of the s t a r  U s i n g these i n t e n s i t y measurements,  those p u b l i s h e d by E . G. W i l l i a m s , and unpublished measures by R. II. P e t r i e , c r i t e r i a f o r determining s p e c t r a l 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 ted.  sugges-  A l s o , 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 w i t h  l u m i n o s i t y , a method of determining a b s o l u t e magnitudes i s suggested.  S p e c t r a l types and l u m i n o s i t i e s as determined  from  these c r i t e r i a are g i v e n f o r 133 B type s t a r s f o r which photom e t r i c measures of l i n e i n t e n s i t y are a v a i l a b l e .  ACKNOWLEDGMENTS  I would l i k e to acknowledge the kind help of Dr. J. A. Pearce, Dominion Astrophysicist, and the other members of the s t a f f 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 t h i s investigation during my work at the Observatory.  E s p e c i a l l y I wish to thank Dr. R. M. P e t r i e , who supervised  the work, f o r h i s many discussions of the problems involved, for the luminosity data he provided, and f o r permission to use his unpublished l i n e i n t e n s i t y 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 t h e i r main absorption features.  The spectral types are u s u a l l y 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  c h i e f l y on the degree of i o n i z a t i o n i n the s t e l l a r atmosphere and thus on i t s temperature.  The degree of i o n i z a t i o n i s indicated by  the  v a r i a t i o n i n i n t e n s i t y of the absorption l i n e s i n the spectrum.  As  the  temperature of the s t e l l a r atmosphere increases c e r t a i n l i n e s increase i n intensity, reach a maximum, and  then decrease.  The temperature at  which a l i n e shows i t s maximum depends on the excitation p o t e n t i a l of the lower l e v e l of the l i n e and.the i o n i z a t i o n p o t e n t i a l of the atom or ion.  These factors determine the r e l a t i v e number of atoms able to  absorb the l i n e observed.  This means that the atoms of high excitation  and i o n i z a t i o n potentials contribute most to the observed spectra the hottest  of  stars, while the l i n e s of low e x c i t a t i o n potential appear i n  the Coolest stars.  - 1 -  2.  In addition, i n each type  ;  a further c l a s s i f i c a t i o n can be made  on the basis of absolute magnitude or i n t r i n s i c luminosity intermediates and dwarfs.  into giants,  This difference i n luminosity i s only p a r t i a l l y  due to difference i n the s t e l l a r mass, while the c h i e f 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  surface gravity differences, cause differences i n the absorption of the stars.  In giants the absorption  to  spectra  l i n e s are sharper and the  inten-  s i t i e s of l i n e s due to m e t a l l i c ions are increased, while i n dwarfs the l i n e s are more d i f f u s e and those due to hydrogen and helium are much broadened due to Stark e f f e c t .  However, not a l l cases of d i f f u s e l i n e s  i n s t e l l a r spectra are due to luminosity e f f e c t s , since high r o t a t i o n a l v e l o c i t i e s of stars tend to produce dish-shaped l i n e p r o f i l e s as a r e s u l t of the integrated Doppler s h i f t over the s t e l l a r disk. An examination of a s t e l l a r spectrum as discussed above w i l l give the temperature and parameter system.  surface g r a v i t y to c l a s s i f y the star i n a  two  However, there i s also c e r t a i n evidence to indicate  that t h i s i s not s u f f i c i e n t d e f i n i t e l y to characterize a s t e l l a r atmosphere.  For example, among the hottest  (Wolf-Rayet) and the coolest stars  there appear differences that can hardly be explained  except as v a r i a t i o n s  i n the abundance of various elements. Among the hottest stars are those of spectral types G and They are comparatively rare, -but owing to t h e i r great luminosity  B.  (a  consequence of t h e i r high temperature) they can be seen f o r large d i s t a n ces i n the galaxy.  For t h i s reason a knowledge of t h e i r motions proves  useful i n a study of the structure of the galaxy.  For t h i s to be of much  value a knowledge of t h e i r distances i s required.  These distances  can  3.  be obtained i f both the apparent and r e a l magnitudes of the stars are known.  To obtain c r i t e r i a f o r determining spectral types and these  absolute magnitudes was the object of the research upon which t h i s t h e s i s i s based.  PREVIOUS INVESTIGATIONS  The Harvard c l a s s i f i c a t i o n i s based on v i s u a l examination of low dispersion objective prism plates.  Most of the revised c l a s s i f i c a t i c n s  from various observatories such as Mount Wilson, V i c t o r i a , and the recent work of Morgan, Keenan, and Kellman  1  a t Yerkes are also based on  v i s u a l examination but of higher dispersion plates.  Of these, the  V i c t o r i a revised c l a s s i f i c a t i o n was made by J . A. Pearce l a r g e l y 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 l i n e i n t e n s i t i e s from spectrpphotometrie measures f o r 0 and B type stars.  These measurements by Williams comprise  about the only extensive l i s t of measured l i n e i n t e n s i t i e s i n the B type stars.  In addition, there are measurements of absorption l i n e i n t e n s i t y  f o r several stars made by Rudnick^ using a w i d e - s l i t photometer method. The application of t h i s method w i l l be discussed b r i e f l y l a t e r . There 1 . Morgan, Keenan and Kellman, An Outline of Spectral C l a s s i f i c a t i o n . 2 . E. G. Williams, Ap_." J . , 83_, 2 7 9 , 1 9 3 6 . 3.  Paul Rudnick, Ag. J . , 83_, 4 3 9 , 1 9 3 6 .  4.  have also been several l i s t s of hydrogen l i n e i n t e n s i t i e s published a few s p e c i a l studies of s p e c i a l stars.  and  These have not been referred to  further i n t h i s discussion owing to lack of information about systematic differences i n measurement between such values and those made at Dominion Astrophyslcal  the  Observatory.  Williams used the l i n e i n t e n s i t i e s obtained i n h i s i n v e s t i g a 1  t i o n to set up a c l a s s i f i c a t i o n  scheme based on measured l i n e i n t e n s i t i e s .  2 However, as discussed by Petrie  i n h i s investigation of the 0 type stars,  Williams' c r i t e r i a are based l a r g e l y on l i n e s of low i n t e n s i t y which are subject to large errors of measurement on low dispersion spectra.  Since  f o r a study of the f a i n t e r and more distant stars i t i s necessary to  use  low dispersion spectra and consequently spectra i n which the weaker i  l i n e s are obliterated, c r i t e r i a based on the most intense l i n e s i n the spectra have to be determined.  This i s also required by the f a c t that  many of these early type stars have shallow d i f f u s e lines, increasing d i f f i c u l t i e s of measurement.  the  In B type stars by f a r the, most intense  l i n e s are those of the Balmer series of hydrogen followed by the l i n e s of the d i f f u s e s i n g l e t 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 i s well known thatJboth  hydrogen ( c h i e f l y i n l a t e r subtypes) and helium ( e s p e c i a l l y i n earlysubtypes) are enhanced i n i n t e n s i t y i n dwarf and intermediate stars to Stark effect caused by intermolecular l i n e i s enhanced i n the giants.  due  e l e c t r i c f i e l d s , while the Mg  II  These f a c t s make, i t undesirable to use  the absolute i n t e n s i t i e s of any of the measured l i n e s f o r c r i t e r i a . This • i s discussed by W i l l i a m s , who comes to the conclusion that r a t i o s of 1  1.  E. a. Williams, A£.J_., 83_, 305,  2.  B. M. Petrie, J . R. A. S. C., .38,,  1936. 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« A l l 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 s l i t 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  follow ]  6.  mercury arc i s photographed with the c a l i b r a t i n g spectrograph spectrum appears next to the c a l i b r a t i o n .  so that i t s  For most reductions i n t h i s  work the c a l i b r a t i o n curve for A 4047 was used f o r the portion of the spectrum between  43933 and-  X 4144  f o r wavelengths between A 4267 and  and the c a l i b r a t i o n curve f o r  A 4575*  A 4358  A few of the oldest plates had  been calibrated with a tube sensitometer illumened by white l i g h t with a filter.  This impressed small spots of varying density on the p l a t e .  From  t h i s type of c a l i b r a t i o n only one mean c a l i b r a t i o n curve f o r a l l wavelengths on the plate could be  obtained.  To obtain the equivalent widths of the l i n e s measured, the usual p r a c t i c e 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 i n t e n s i t y record, the 2 semi-automatic intensitometer also described by Beals  was used.  Most of  the records were reduced i n two stages, the galvanometer d e f l e c t i o n  being  f i r s t reduced to a "log i n t e n s i t y " scale and on t h i s the l i n e of the continuous  spectrum was  drawn.  The second stage consisted of transforming  the "log intensity" to a true intensity curve, keeping the spectrum at a height of 10 inches on the paper.  continuous  The s i x Pleiades s t a r s  were measured l a t e r and reduced i n only one stage d i r e c t l y to the true i n t e n s i t y , but with varying height of the continuous  spectrum.  The i n t e n s i t y of the absorption l i n e s was measured by drawing freehand a mean p r o f i l e among the i r r e g u l a r i t i e s due to grain e f f e c t i n the o r i g i n a l plate as shown i n Plate H . and the l i n e of the continuous  The area between t h i s p r o f i l e  spectrum was measured with a planimeter.  The planimeter readings were converted to the i n t e n s i t i e s of the l i n e s  I"!  cTsT Beals,  2.  C. S. Beals, J.R.A.S.C., _3j5,  M. N.,  96, 730,  1935. 44,  1944.  7.  i n equivalent Angstroms, i . e . the width of the l i n e of rectangular p r o f i l e and depth equal to the height of the continuous  spectrum which  would absorb the same t o t a l amount of energy from the continuous as the actual l i n e does.  spectrum  For l i n e s i n the wing of the hydrogen l i n e s the  residual i n t e n s i t y of the wing at the p o s i t i o n of the l i n e being measured was taken as the l e v e l of the continuous  spectrum f o r t h i s purpose.  In addition t o the i n t e n s i t y measures the apparent depth of the centre of the l i n e p r o f i l e was measured f o r the hydrogen and helium as a f r a c t i o n of the height of the continuous  lines  spectrum.  •  ERRORS IN STELLAR SPECTROPHOTOMETRY  S t e l l a r spectrophotometry i s not of extreme accuracy.  The  reasons f o r t h i s l i e i n the d i f f i c u l t i e s attendant upon the small l i g h t intensity received from the s t a r s .  In order to obtain spectra with a  reasonably short exposure only a short s l i t can be used i n the s t e l l a r spectrograph,  since the s t e l 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-  t i e s introduced by the random e f f e c t of plate graininess are of f a i r l y large magnitude. continuous tracing.  This effect causes uncertainties i n the p o s i t i o n of the  spectrum and of the mean p r o f i l e of the l i n e s as drawn on the In spite of the small length of s l i t , with good seeing the  s t e l l a r image i s too small to cover the whole s l i t length.  In order to  obtain even i l l u m i n a t i o n of the s l i t t h i s 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 w i l l have been exposed to different positions of the characteristic curve .of the plate used, while the microphotometer records an average blackening 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 i s such as to cause i t to l i e on the toe of the characteri s t i c 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  Hy  Line  Helium I  •r w i  ,7.0  Poor Plate Good Plates  D  D  w  0.75  8.5  0.75  5 . 8 ' 0.62  5.8  0.68  Mgll  4026  .  4009 • ¥ D  ;  0.44 0 . 2 2  1.40  O.46 2.14  0,' 42 0.16  1.03  a  (  ¥  '  D  4471 ¥  4481 ¥  D 0.57  0.71  38 0.9C 0 . 3 3  0.33  j  •  4  i i i I t  '  This example i s an extreme one, since the plate in error i s very noticeably poorly exposed, but a small amount of the same effect must remain in the spectra measured although i n a l l other cases apparently evenly exposed plates were used. On account of these almost irremediable errors in the spectrographic 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 f o r t h i s i s the fact that  many of the l i n e s are extremely d i f f u s e and hence t h e i r measured i n t e n s i t ies w i l l be very sensitive to errors i n drawing both the l e v e l of the continuous spectrum and the mean p r o f i l e . • In l a t e r type stars, where the l i n e s 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 d i f f u s e l i n e w i l l cause a large error i n the measured area.  MEASUREMENT OF LINE INTENSITIES  Table I I gives the measured l i n e i n t e n s i t i e s i n equivalent Angstroms.  For the Hydrogen l i n e s and stronger Helium I l i n e s the inten-  s i t y i s given i n the column headed W, while that headed D gives the r e l a t i v e depth of the centre of the l i n e .  The i n t e n s i t i e s 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 c o n s t e l l a t i o n name.  Then comes the  v i s u a l apparent magnitude, while the next three columns give the spectral type, f i r s t as assigned at Harvard by Miss Cannon and l i s t e d i n the Henry Draper Catalogue, then the V i c t o r i a Revised type, as given by J . A. Pearce from v i s u a l estimates, these measured i n t e n s i t i e s . 1^  1  and l a s t l y , types as determined  The next two columns give the absolute  Pub. D.A.O., v o l . 5 , No. 2 , 1 9 3 1 .  from  10.  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  l i n e was not noticeable on the tracing, a question mark that the presence of a s l i g h t absorption i s doubtful, while a blank means, i n general, that no detailed examination has been made.  In the case of l i n e depths, the  blank means that, although an i n t e n s i t y has been measured, the l i n 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 t h i s case, unless the two spectra coincide, the depth  measurement has no meaning. In Table I I I are given l i n e i n t e n s i t i e s of | 4 0 r i o n i s , 0(  B:8,  Lyrae, AO, and o< Cygni, A 2 , as determined by measuring with the p l a n i -  meter the p r o f i l e s published by ?filliams and H i l t n e r . *  The two  A type  stars were measured to see that the c r i t e r i a obtained would not be inconsistent with a smooth junction with the A type s t a r s . In addition to the stars measured i n t h i s program, there have also been used i n the discussion of r e s u l t s , measurements f o r 27 B stars made by R. M. Petrie, p a r t l y f o r t h i s program and p a r t l y i n h i s work on binary stars.  These measurements are mainly unpublished.  The measure-  ments given by Williams^ f o r 64 stars have also been, used, since a comparison of measures by the different measurers, III, f i g . 1,  as plotted i n Plate  indicate no serious systematic differences.  The values of l i n e i n t e n s i t i e s i n equivalent Angstroms from these three sources have been plotted against the Henry Draper for H, Hel, Mgll, and CII i n Plate I I I , f i g s . 2 , 3 , 5, 6 .  subtype  For hydrogen  i n f i g . 2 the mean of H Y and H/ has been plotted, f o r neutral helium 1. W. A. Hiltner and R.C. Williams, Photometric A t l a s of S t e l l a r Spectra. 2 . E. G. Williams, Ap. J . , 8J3, 279, 1936.  11  the mean of the four l i n e s A 4 0 2 6 , ^ 4471 (diffuse t r i p l e t s ) , and  \ 4388,  A4144 (diffuse s i n g l e t s ) , f o r ionized magnesium the l i n e  and f o r ionized carbon the l i n e  \ 1+267 has been plotted.  A.4481,  In f i g . 4 the  r a t i o of the sum of the i n t e n s i t i e s of the two singlet l i n e s to the sum of the i n t e n s i t i e s of the two t r i p l e t l i n e s has been shown.  Subtypes  4 , 6 , and 7 are missing from a l l graphs because they are not used i n the Henry Draper c l a s s i f i c a t i o n . The very large scatter shown i n a l l graphs i s partly due to poor c l a s s i f i c a t i o n .  This portion should be removed by the use of a  c l a s s i f i c a t i o n scheme based on measured l i n e i n t e n s i t i e s .  This w i l l not  remove a l l the scatter apparent on the diagrams, since there are v a r i a tions i n i n t e n s i t y i n each subtype, due to luminosity effects,  variations  due to errors i n measurement, e s p e c i a l l y of weak l i n e s , and probably also variations stars.  due to other natural differences between the i n d i v i d u a l  12.  TABLE I I - STELLAR DATA  HenryDraper Number  Appt. Mag..  Name  9531 Boss 340 10516 f Persei 11415 S Cassiopiae 17573 41 A r i e t i s 20315 30 Persei 20319 20365 29 Persei 20418 31 Persei 20809 Boss 767 21362 Boss 783 21428 34 Persei 0 Persei 23180 23324 Boss 855 23432 Boss 8 6 l 23441 +24°556 23753 Boss 872 23850 Boss 877 23950 25940 48 Persei 29763 f Tauri 30836 irh- Orionis 31237 77-5 Orionis 33328 X E r i d a n i 35039 22 Orionis 35411 7[ Orionis A 35468 X Orionis Orionis 35715 36267 A Orionis 36822 ^'Orionis 37742 y Orionis b r 37756 Boss 1 3 9 9 42560 £ Orionis 45542 -p" Geminorum 58715 P Canis Min. 109387 x Draconis 116658 <*Virginis 144217 B' S c o r p i i 149212 15 Draconis 155763 if Draconis 177756 \ Aquilae 180554 1 Vulpeculae 196867 << Delpnini 198667 5 Aquarii 202904 V Cygni 212120 2 Lacertae 1  v  5-77 4.19 3-44 3.68 5.38 6.02 5.30 5.08 5.30 • 5.64 4.67 3.94 5.63 5-85 6.46 5.51 3.80 5.92 ' 4.03 4.33 3-78 3-87 4.34 4.65 3.44 1.70 4.66 4.32 4.53 2.05 5.00 4.35 4.06 3.09 3.88 1.21 c 2.90 4.98 3.22 3.55 4.60 3.86 5.50 4.42 466  . Spectral 1 Meas'd ED MeasM Abs. Vict. Revd. Mag. B9 BOp B3 B8 B5 B9 B3 B3 B3 B5 B5 Bl B8 B8 B9 B8 BS B9 B3P B5 B3 B3 B2 B3 Bl B2 B2 B3 BO BO B3 B3 B5 B8 B5P B2 Bl B8 B5 B9 B5 B8 BS  33P B5  B8 B3.5 B7-5 B6 B7 B3  BOne B5s  -  B7n -  B3 B3 B3 B8nn B5 B2k  . -  -  -  -  B3e B5n  B2s B2s B3nk B3ns BOk jB2s B2 B4n BOssk BOnk 33  B3nn  B5ne  -  B5e B2 B2k  -  B8s  -  B5n . B3nek  B5  B4  1  B4 B5 B3.5 BO.5 B7 B7 B9 B7.5 B7 B9.5 B3 B3.5 B2 Bl Bl B1.5 Bl B2 Bl B5 BO. 5 BO Bl B3 B5 B8 B5 B2 B2.5 B9.5 B7.5 B9-5 B3-5 BS  B9.5  B2  B4.5  +2.3  -  -1.3 +1.1 +1.6 +1.4 -0.1 -1.2 -1.3 -1.8 -0.3 -2.8 +0.5 +1.7 +2.2 +0.3 -0.7 +1.1 -2.2 +0.9 -3.0 -2.8 -2.1 -1.5 -1.8 -2.0 -1.7 +0.1 -2.6 -4.7' -1.6 -0.5 -1.1 -0.4 -2.0 -2.9 -2.0 +2.9 -2.3 +1.9 -1.5 +1.3 +0.1 . -1.5 -0.8  Plates  2 2 2 2 2 1 1 1 1 1 2 2 2 2 2 2 2 2 1 1 2 2 2 2 2 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2  13.  TABLE I I (Cont'd)  INTENSITY MEASURES •  H.D. No,  Helium I  Hydrogen .  y(4340)  w 9531 10516  12.00  11415 17573 20315 20319 20365 20418 20809 21362 21428  5-84 10.44 9.29 9.80  23180  D .71  em  6.44 6 .19 6.52 7.02  .68  (4101)  ¥  D  11.28 em 5.80  .72  0.52  -  0.75 0.90  10.06  .72  11.20  .59 •.50  5.88  9-15  6.64 6.08 6.62  .62 .68 .64 • 70 .60 .51 • 56 • 53 .61  w  0.50  .11  1.15 1.02 0.92  .26  0.69  6. 60  3.49 9.58  • 52 .62  2.73 9.78  .50  1.04 1.07 '  .64  0.41  11.38 11.52  .70 .66  10.44  .71  23441  II.69 -  23753 23850  9.46 8.25  .59 .62  • 71 .61 .62  0.57 0.21  23950  10.62  •75  25940  4.77 8.40  em .61  7.80  3.92 3.96  • 54 .52  4.34 4.92  • 37 .64 2sp  3.59 3.19 3-83 4.66  29763 30836 31237 33328 35039 35411 35468 35715 36267 36822 37742 37756 42560  4.75  4.88 5.03 7.66 3.75 1.74 4.50  58715  6.64 7.12 9.20  109387 116658  4.28  144217 149212  II.69  45542  155763 177756 180554 196867 198667 202904 212120  6.02 4.35 5.68 10.79 5.76  IO.46 9.32 5.05 6.74  7.85 9.70 5.16  .72  em .63 • 56 .48 • 38  .62  .52 2sp  3-85 4.38 4.06  .52  .60  7.72  .60  .50  0.36 0.34 0.21 0.86 1.64 1.13  1.18 1.28 1.50 1.42 1.18  2.77  .46  1.45 0.89 1.29  .38  1.49  • 34  0.88  .51 .56  4.51 6.29 6.26  .51 .60  1.43  .55 .55 .44 2sp 2sp • 75 .62 .66 .56 • .68 .74 • 38 2sp  9.56 4.80  .58 .66 .48  3.52 5.37 13.20 6.42  11.36 5.67  10.28 8.96 5.02  6.80  .10  0.41 0.66  6.89  8.98  D  .33 .10 .10  • 51 .60  23324 23432  4026  4471  i  .65 .62  .54  .  1.28 0.82  0.43 0.70  .17  .18  .13 .24 • 36 .09 .10 .05 .06 .07  .08  • 38 0.49 .12 0.60 .12 0.48 .10 1.14 1.24 0.97 O.58  .18 .48 .36  0.94 1.19 1.25  .07 .13 .26  0.22 0.48 0.23  0.48  0.33  .05  0.14  0.75 0.72 0.6l  .18 .19 .30  .34 .20  O.63  .29  0 . 4 4 .12 0.64 .17 0.53 .27 O.63 . 2 4  .50  0.86  .32  0.42  0.81 . 1 2  • 30  0.80 . 3 3  .09 .28  0.28 .08 0 . 3 2 .21  0 . 3 0 .11 O.76 . 2 6 0.70 .18  0.20 .07 0.89 .29 0.67 .18 0.23 .08  0.75 0.97 0.37  0.71  .21 .06 .26  0.45 0.26  •07  0.46 0.68  • 13  -  • 41  0.49  0.10  O.76 .08  .11  0.55 0.98 0.72  1.21  .12  .04  ?  .42  0.74  0.24 0.42 0.21  .14 • 30 .06 .08  0.09 .04  0.28  1.18  0.41  .09  0 . 2 5 .08 0 . 4 8 .15 0.70 .13 0.35 .09 0.42 .08 0.60 .18  .07  1.02  .18  0.84 0 . 5 0 • 23 0.10 0.18  .04  0.88  0.84 . 7 3 ' O.36 O.23 .75 1.25 •47  .24 .07  --  0.14 0.32  .15 .07 .10 .10 .10  1.31- • 3 9 1.24 .30 0.61 .16 0.33 .06  .17 .06  0.66  D  .24 0.17 . 0 5 0.15 . 0 6 0.06  .35 .29 .14 .08  0.33 0.30  0.12  .08  .40 .26  .18  .06  0.41 0.68 0.66  .43 1.18 0 . 8 6 .22 1.02 .38 0.57 .21  .18  0.34  .11  1.00 . 4 2  1.33  ¥  .20 .10  1.20 .32  0.53 0.34  D  0.74 0.64 0.46  1 . 0 3 • 41 0 . 5 0 .11 0.59 0.27 0.42  ¥  4144  • 31 .21 .26  • 37 .36  .08  0.77  .12  0.74 1.08  1.00 . 2 4  0.29  .67 .58  0.38  D  .19 .30  1.19 1.12 .78 •70  ¥  4388  0.19 0.48 0.59 0.07 0.18  .06  .09  0.14  .09  O.96 0.30 .07 0.20 .11 1 . 2 5 .28  0.58 0.27 0.12  .05  0.60 .15 0.04 0.08  0.75  .19  0.79  0.86  0.39  .12  0.47  .19  14.  TABLE I I (Cont) H.D. No.  INTENSITY MEASURES  He I Mg I I 4121 4481 4009  9531 .... 10516 0.42 11415 17573 20315 20319 • 20365 0 . 4 4 20418 0 . 2 1 •? 20809 •> 21362 21428 0 . 4 8 2318O 0 . 4 5 23324 23432 234U • 23753 •?' 23850 23950 25940 0 . 3 5 29763 0 . 4 3 30836 O.60 31237 0 . 4 7 33328 O.48 35039 0.57 0.48 35411 35468 0 . 5 7 35715 0 . 5 3 36267 0.18 36822 0.28 37742 0 . 0 7 37756 0 . 7 3 42560 0 . 4 9 45542 0 . 2 0 58715 109387 0.16 116658 0 . 4 0 144217 0 . 3 6 149212 155763 0 . 2 1 177756 180554 0 . 4 4 196867 198667 202904 0 . 5 5 212120 .0.22  -  -  -  0.24  -  0.09  ' -  0.14 0.25 ?  0.12 0.29 0.41 -  -  -  --  0.14  0.28  0.33 0.40 0.30 0.47 0.35 0.40 0.37 0.22 0.27 0.17 0.40 0.24 0.05  0.08 0.32 0.42  -  0.09  -  0.12  -  0.24 0.16  C II Call 4267 3934  (K) 0.22  0.43  -  0.33 0.29 O.58 O.40 0.31 0.31 0.21  flaw  0.31  0.18 0.34 0.57 0.26 0.31 0.29 O.36 0.39  0.28  0.31 0.29 0.22 0.32 0.22 0.32 0.15 O.26 0.20  -  0.39 0.33 0.44 0.42 O.29 0.26 0.28 0.54 0.25 0.39 0.38 0.41 0.39 0.29 0.35  Si II 4128 4131  0.20  0.22 0.19 0.14 ?'  0.18  -  0.26 0.11 0.14 0.49 0.24 0.14  0.13  0.08  0.09 0.04 0.18  0.10 0.08 0.13 0.13  0.18  0.18  0.10  0.19  0.04 0.14 0.14 0.10 0.07 0.10 0.14  0.09  0.12  0.04  0.06  0.18  0.18 0.17  0.18 0.25 0.34 0.13 0.29 0.24 0.28 0.13 0.12 0.06 0.24 ?  -  0.25  0.31 0.15 0.04 0.10 0.29 0.12 0.25 0.24 0.19 0.13 0.19 0.13 0.11  0.08  0.12 0.24 0.13 0.14 0.20 0.26 0.14 0.05 0.03  0.18  0.58 0.14 Q.l6 0.21  0.20 0.20  0.32 0.07 0.25  0.09  0.42  4089  0 II 4070 4072 4U7o  -  «?  0.04 0.22 0.23  S i IV  0.12 0.07 0.05 0.09  -  0.11  0.06  0.17  0.14  0.11  0.18  0.14 0.10 0.09 0.04 0.12  0.18 0.02 0.11  .10 .15 .06 .07 .08 .07 .11 .08  :o7  0.08  0.06 0.11 0.12 0.09 0.14  .23  .18  .12 .13 .10,  •ft  .09  47 .16  .18  0.08  .07  .06  .12  0.04 0.10  .'07  0.07 0.21 0.03 0.22 0.09  .13  .25  0.37 0.55 0.02 0.14 0.04  .19  •3?  .06" .07'  TABLE I I (Cont.)  H.D.No. •  -  9531 10516 20319 2318O 30836 31237 33328 35039 35411 35468 35715 36822 37742 37756 144217 149212 177756 196867  He II cm Hel 4553 4568 .4575 4116 3995 4097 4233 3920 4069 3927 4200 4542 SilV N i l  Si I I I  N U T F e l l CII  0.12 em  0.12  0.03 0.43 0.37 0.08 0.07 0.20 0.12 0.18 0.07 0.24 0.18  mm  0.13  0.28 0.25 0.16 0.21 0.08  0.35 0.20  0.06  0.22 0.04  0.08 0.11 0.12  0.04 0.22 0/08 0.21 0.28 0.1C  0.17- 0.05  0.35 0.45  ?  0.20  0.22  0.17  0.46  0.12  0.16 0.18 0.08  TABLE I I I - MEASUREMENTS FROM TRACINGS IN ATLAS H.D. No.  Name  34085 /3 Orionis 172167 ^ Lyrae 197345 o(Cygni< H.D. No.  34085 112167 197345  H.D. Type  Appt. Mag.  0.3  0.1  Hel  Hel  4121 Hel  0.37  0.22 0.03 0.03  0.17 0.04  4101  HY  HS  1.86 19.5 1.3 2.86  B8p AO A2p  4i44 4009  ^Equivalent  1.4340  2.02 14.7 3.04  Widths  4471 Hel  Hel  0.50 0.57 0.09 0.13 0.18 0.12  0.25  4267  4128  MgH.  Call  CII  Sill  0.53 0.26 0.90  O.63 O.16 0.78 0.14 0.60  0.23 0.33 0.06 0.35  Fell  4388  Hel  3933 4233  4481  4026  4131 Sill  0.32 0.05 0.34  0.04 '  PLATE IE  H.D. T y p e  To f o l l o w page 15  16.  SPECTRAL CLASSIFICATION  •|  With the exception of the work of W i l l i a m s , p r a c t i c a l l y a l l 1  c l a s s i f i c a t i o n s so f a r published of the B type stars are based on v i s u a l examination of plates of the s t e l l a r spectrum.  In t h i s category, f o r  example, f a l l the determinations of Miss Cannon f o r the Henry Draper catalogue which are based on the c r i t e r i a given i n the introduction t o the catalogue , the Y i c t o r i a Revised c l a s s i f i c a t i o n , by J . A.. Pearo% using 2  v i s u a l estimates of l i n e i n t e n s i t y 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 v i s u a l estimation methods enable an  experienced person to c l a s s i f y spectra r a p i d l y and f a i r l y consistently. However, such methods do not guarantee absolute agreement between d i f f e r ent observers, even when using the same plates as Tables I and I I given by 3 Williams and Edwards show.  A more serious d i f f i c u l t y l i e s i n the fact  that an inexperienced observer cannot take the c l a s s i f i c a t i o n c r i t e r i a given and expect to produce r e s u l t s 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 v i s u a l method are  that i t i s almost impossible to use the same v i s u a l c r i t e r i a f o r plates of a l l dispersions, hence introducing inconsistencies, and that errors are introduced by the usual d i f f u s e l i n e s (often caused by r o t a t i o n a l e f f e c t s ) , by poor exposure, and by luminosity e f f e c t s , since they cannot be 1. 2. 3. 4.  v i s u a l l y estimated with p r e c i s i o n . E. G. Williams, Ap_. J . , 83_, 305, 1936. Harvard Annals, 9 1 , Z, 1918. E. S. Williams ancT D. L. Edwards, M. N., 98 , 4 6 7 , 1938. Morgan, Keenan, Kellman, An Outline of S t e l l a r C l a s s i f i c a t i o n .  17.  A c l a s s i f i c a t i o n scheme based on measured l i n e i n t e n s i t i e s should be f r e e from these disadvantages since i t i s based on objective measures of the l i n e i n t e n s i t i e s , which should be the same f o r a l l observers, rather than on subjective estimation which w i l l c e r t a i n l y 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  of t h i s type, but,  1  provide an objective scheme  as discussed above, i t i s c h i e f l y based on measurements  of weak l i n e s which are d i f f i c u l t to measure accurately on low  dispersion  spectra, e s p e c i a l l y . i f the l i n e s are at a l l diffuse i n character. Theoretically  a. c l a s s i f i c a t i o n scheme based on r a t i o s of  i n t e n s i t i e s of l i n e s due  the  to the same element i n d i f f e r e n t stages of i o n i z -  ation would give a good i n d i c a t i o n of temperature since i t should be independent of abundance e f f e c t . l i n e s due  to S i l l , S i I I I , and  For example, since i n B type spectra  S i l V appear, i t should be possible to base  a c l a s s i f i c a t i o n on the r a t i o s S i l l / S i l l l and  SiHI/SilV.  However,"  t h i s does not appear very p r a c t i c a l since the l i n e s are of low  intensity, .  and hence are unsuitable because of the e f f e c t of accidental errors i n . measurement. Another possible t h e o r e t i c a l  c l a s s i f i c a t i o n could be based on 2  extension of the argument suggested by Goldberg d i f f u s e singlets to the diffuse t r i p l e t s of Hel. Plate H I ,  for the r a t i o of  the  However, as shown i n  figure 4, the measured results show considerable v a r i a t i o n  t h i s r a t i o within one  in  spectral subtypej together with a f l a t maximum f o r  the mean values i n the early subtypes.  Further consideration also shows  that even on a t h e o r e t i c a l basis curve of growth effects and 1. E. G. Williams, Ap_. J., 83_, 310, 193°. 2. Leo Goldberg, Ap_. J., 89_, 623, 1939.  the l i n e  an  18.  broadening due to Stark effect would complicate the r a t i o and prevent i t s p r a c t i c a l use. The outstanding v a r i a t i o n i n B type spectra i s the increase i n i n t e n s i t y of the l i n e s of the Balmer series of hydrogen with decreasing temperature.  The hydrogen l i n e s also increase so much i n i n t e n s i t y with  decreasing luminosity that they can only be used f o r type c r i t e r i a i f the absolute magnitude i s already reasonably well known. Hence i t appears that a p r a c t i c a l scheme w i l l have to be based on r a t i o s of.the l i n e s of highest intensity, i . e . those of hydrogen, h e l ium, and ionized magnesium.  The greatest change i n r a t i o s between sub-  types occurs i n the case where one member of the r a t i o i s increasing i n i n t e n s i t y with advancing type, while the second i s decreasing.  Since the  hydrogen and magnesium l i n e s increase i n i n t e n s i t y with decreasing temperature, while the helium l i n e s f i r s t increase i n i n t e n s i t y , then reach a maximum and decrease, the, obvious r a t i o s to t r y are those of hydrogen to helium and magnesium to helium.  However, since both hydrogen and helium  l i n e s are enhanced i n dwarfs, although hydrogen to a greater extent, while the magnesium l i n e i s enhanced i n the giants, i t i s obvious that one r a t i o w i l l not be suitable f o r a i l luminosity groups.  Hence a f i n a l  c l a s s i f i c a t i o n cannot be assigned u n t i l the luminosity has been determined, S i m i l a r l y to obtain the correct luminosity a knowledge of the spectral type i s required (see next section).  However, the c r i t e r i a a r e 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 v i s u a l examination of the spectrum or otherwise) enables a f i n a l determination to be reached f a i r l y r a p i d l y . The r a t i o s suggested as suitable f o r type c r i t e r i a are given  19  i n Table I? and plotted i n Plate IV, figures 7 and 8.  The r a t i o H/Hel  i s the r a t i o of the mean i n t e n s i t y i n equivalent Angstroms of to the mean intensity of the Hel l i n e s  A4471,  A4026,  \h3&8, and A 4144.  \448l to the mean of  The r a t i o Mgll/Hel i s the r a t i o of the M g l l l i n e the four Hel l i n e s .  and K$  The H/Hel r a t i o was given greater weight i n the early  subtypes where the Mgll l i n e i s weak. The l i n e depths measured along with the i n t e n s i t i e s have not been used f o r c l a s s i f i c a t i o n purposes because of the f a c t that the recorded e f f e c t i s not due wholly to the true l i n e depth but i s considerably modified by the spectrograph by d i f f r a c t i o n effects.  i n r e d i s t r i b u t i n g the l i g h t i n the spectrum  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 v a r i e t y of spectrographs with d i f f e r e n t dispersions.  TABEE IV - SUGGESTED TYPE CRITERIA  Ratio H/Hel  Type Giants  Intermediates  Ratio Mgll/Hel  Dwarfs  Giants  3.6  0.44  0.10  4.4  0.48  0.16  Intermediates . and Dwarfs  BO  2.0  3.6  Bl  2.4  4.. 4  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 •  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  •  . 0.86  eo  PL AT EE? r  Fig. 7  ClassificationfatfoI A  Giants  B  Inter mediates  C  Dwarfs  Fig. 8  yjfe.  C l a s s i f ic^tior, R a t i o IE  -jgf  30  2 0  '0  gio  il 'i2. i3 <f iS" i 6 - i7 , 8 glflio  ,1 ,2 • 3  ,5 ,6 ,7 ,8 ,3  A  10  J  I  Absolute M a g n i t u d e _j l i  I -+  i  i  L  J  L  To f o l l o w -oage 19  20.  LUMINOSITY CRITERIA  The main e f f e c t of luminosity apparent i n a B type s t e l l a r spectrum i s the very large increase i n the strength of the hydrogen l i n e s due to Stark e f f e c t .  To enable luminosities to be determined from the  measurements of t h i s program i t was necessary that the stars o r i g i n a l l y used have known absolute magnitudes.  As the results obtained are to be  used to study g a l a c t i c structure, i t i s desirable to use distance c r i t e r i a obtained independently  of consideration of galactic structure. 1  ute magnitude c r i t e r i a used by Williams  The absol-  were based on distances determined  by measurement of the i n t e n s i t y of the K l i n e s due to i n t e r s t e l l a r calcium, which i n turn he c a l i b r a t e d against distances determined from g a l a c t i c motions.  Tne stars chosen for t h i s program were l a r g e l y those whose d i s -  tances were known from non-spectroscopic  criteria.  These included s t a r s  with known trigonometric parallaxes of greater than 0 " . 0 1 0 and  other  stars whose parallax could be computed from group or c l u s t e r motions. For most of the stars used Dr. R. M. P e t r i e computed absolute magnitudes from t h i s data and i n a few cases gave the magnitude as determined from  2 the K l i n e i n t e n s i t y by using the r e l a t i o n s h i p given by Evans. For the s i x Pleiades stars the absolute magnitudes were kindly calculated by 3  Dr. J. A. Pearce, using the cluster p a r a l l a x as calculated by him . The material used i s n a t u r a l l y rather weak i n 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.  21.  choice of stars with r e l a t i v e l y large trigonometric parallax r e s t r i c t s the distance.  x  By using the absolute magnitudes as obtained above a plot (Plate IV, figure 9) of t o t a l 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 c l a s s i f i c a t i o n as developed above has been . applied to the stars measured, the results being included i n Table I I , and to the stars measured by Williams and by Petrie, f o r which the results are given i n Table V.  This table i s arranged similarly to the f i r s t  columns of Table I I . In the l a s t 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 V i c t o r i a Revised type are shown i n 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 l i n e s , tending to obliterate the weak lines, makes the spectrum appear l a t e r 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.  358  698  886 I486  3360 4180 4727 5394 13854 14134  ;  21291 22928 23480 24398 24534 24760f 25833 28446b 28446f 29376 32343 32630 34085 34333 35497 36371 36862 37128 37202 38771 39698 40111 41H7 41534 44701 44743 58050 74280  Appt. Mag;  . Name o< Andromedae  2.15  7.08  +57°28  Y Pegasi TV Cassiopeiae J Cassiopeiae Cassiopeiae •p Andromedae y* Cassiopeiae Boss 507 Boss 519 Boss 781 b Persei Boss 865 J Persei X Persei 6 Persei f  2.87  var  3.72  4.70  0  4.42  2.25 6.42  6.66 4.42 3.10 4.25  2.91  var  •330785  1 earn b I Cam f  '  +70676  Boss 1195 7\ Aurigae (3 Orionis (3 Tauri X Aurigae X Orionis f £ Orionis J Tauri ^ Orionis Boss 1464 Boss 1475 yc orionis Boss 1517 1  2  r 3 ° 1413  (#Canis Ma +15  0  1564  7\ Hydrae 7\Leonis c< Leonis Boss 2748 p. Leonis  87737 87.901 89688 91316 93521 +38° 2179 L00600b 90 Leonis L00600f | 90 Leonis  b  f  8.1 6.61 5.86 6.61 6.89  H.D.  -  B5  B2 . B9 B3  B2  B3  BOp Blp BO  , -  B2sk B5n B5s BOnne BOsk B2sk  Bl BOp  B8n B7n Bis BOnne  B3  B3k  B5 B5  .  -  Bl Bl  B2nk BOsk B5k B3e  B5  B3  '-  BS  Bl  B3ss Bisk •' BOk B3e BOk  Meas^ urer.  BS .  -1.1  B5.5  -3.5  P P  BO B3P BO  4.71  B2p^  B2 B3  5.64 6.58  B5  1.99  Bl  B3 B3  AOp  B8.  B3 '  B3  BOp B3.  B3 B3  Bl B8 B2 B3 . B4 BO. 5 BO B2 B9 B4.5  B6 B2 BO B9 B3 Bo BO. 5 B3 B3  .  BOsk B3nn  B3 fi  5  -4.0  +6  .  ¥ W  ¥  W  ¥ ¥ P ¥  -0.4 -2.7 -1.8  W  -l.l  P W W  -5.7  -5.4 -0.1 -5.2 +1.6 -5.2 -1.6 -3.1  -6.3 +0.1 -0.8 -3-8 -1.7 -1.5 -3.1 -0.7 -1.5 -4.9 -2.4 0.0. +0.1  w p w ¥ W  -  B5.5  BO. 5 BO B3 B5  w .  -1.8 -0.6 -4.9  -2.7 -1.1  S B1.5 "  P  -5.5 -5.3  B2.5  B7 B2  W  -2.0 +2.7 -2.0 -2.6 0.0  -1.8 -2.7  B2 BO BO.5 B3 BO. 5 B3 BO.5 BO BO B2ssk ' BO Bl B3 B5n B3.5 Blss Bl B3e B3 B5n B1.5 . B4 B6n B7  0e5  B2  7.3  B2ss  -  B9P  5.89 4.90  6.37 4.32 3-58 1.34 6.53 3.85 6.89 6i0  Vict. Revd.  AOp  5.31 B3P 3.28 B3 0.34 B8p Bl  1.78 4.88 5.56 1.75 3.00 2.20  Meas'd Abs. Meas^ Mag.  . Spectral Type  .  w p ¥ ¥ ¥  Iff  ¥ . W  ¥ - ¥ ¥  W  P ¥ W  ¥ W w ¥ W ¥  ¥ ¥  23  TABLE V (Cont.) TYPES FOR STARS MEASURED BY OTHERS H.D. No.  120315 136175 139892 147394 148184 148479 149438 149757 149881 156247 156633 160762 162732 164353 169454 175227 180939 185507  Name  t\ Ursae Ma U Coronae Bor  1.91  &  GC7352  -fr X cA V H  5.07  Herculis Ophiuchi Scorpii f Scorpii Ophiuchi  193536  b  +14°3086  U Ophiuchi A. Herculis 1 Herculis Boss 4 5 1 4 Boss 4 5 4 8 DI Herculis RS Vulpeculae  C Aquijae 187811 Boss 5068 Boss 515O 190603 190967 192422  Appt. Mag. H.D.  var  3.91 4.85 6.5  2.91 2.70 6.59  var var  3-79 6.43  3.92  6.8  var var 5.17 4.91 5.69  7.92 +38°3956  7.10  +45 3139 +4004150  7.05  G  6.28  194279 197911 198478 198846 199081  Boss 5 3 6 I Y Cygni Boss 5375  4.89  199140  +27 3909 o  200120 Boss 5410 204172 Boss 5512 205021 fl Cephei Boss 5563 206165 208185 +62°1992  7.9  221253 224151  Boss Boss  228911  6046 6l42  +2.7  Bis BOnnk B2k  B0 BO B2 BS  • B5nk  B3  B3  B3  BS B5p BO A B3  B3 B3  B3s  -  B8s  -  B5  B3  B5ne  BO  BOssk  B2 Bl BO  BOsk B2k BOsk  B3  B5  -  B3 BOp BO Bl B2p  5-84  3.32 4.87  7-7  6.28  4. 89 N  6.05  B3  B3 B3  B2 Blp  B3 B3 B5 B3  BO B3  B5  B2.5  6.44 4.86  8.4 4.64 4.54 6.83  +64°1717  B5.5 B3.5 BO  B3k  +55°2756  216014 218066  +0.7 +1.6  B3  212455 213420  B3  4.68  208947  7T Aquarii Boss 5810  B3n B3 B8n B7s B3e  B2sk 08nnk  7.10  212571  B5 B3 A3  Meas'd Abs... Mag.  B2 B2  var  +6102216 +6501691  208392  B3  B8 B8  Spectral Type Meas'd Vict. Revd.  Bis B3nne  BOk. Bl B2sk  -  B3nnk B3k  -  Blnnek  B3k  BOk  . B3k  BOk  BO. 5 B2 BO B3-5  B3 B3  +0.7  -2.6  +1 -2.2 -4.2 -3.2  -0.5 -0.2 -3.6  0.0  B9  B6  -5.0  B2 B4  -0.9  -5.4  B5  Bl  B2.5  BO BO BO Bl BO  -3.3 -4.7  -1.2 -5.5  B2.5.  Bl Bl ' B3 B2.5  B3 BO BO.  5  B1.5  Bl Bl Bl  B3-5  Bl BO. 5 BO. 5 B2 B2 BO.5  BO  0.0 -0.1 -1.1 -5.8  -3.0  -5.9 -3.2 +1.3 -4.0 -0.4 -4.0 -1.6 -5.3  -0.2 -1.5  +0.8  -5.0 -3.9  -1.6  -1.1 -2.1 0.0  -3.8 +0.5  Measurer  ¥ P P  ¥  W W  ¥  W W P P  w ¥ ¥ ¥  P P P  ¥  W P W P  ¥  • P  ¥ P P P  ¥ ¥ ¥ ¥ ¥ Iff ¥ ¥ P P P  ¥  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 photometrically measured l i n e 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 l i n e intens i t i e s are given took the greatest part of a four-month summer assistantship 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 i n speed can be obtained by restricting the spectral regions measured to the lines being used for c l a s s i f i c a t i o n .  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 r e l a t i v e l y large probability of error i n 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 s t e l l a r spectrum are measured should prove about as satisfactory, as the system here suggested. four lines suitable for t h i s purpose are Hy at singlet at A 4481.  A4388,  The  4340, the Hel diffuse  the Hel diffuse t r i p l e t at ^4471, and the Mgll l i n e at  These have the advantage that they a l l l i e i n 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 t h i s scheme  would make very l i t t l e change i n the intensity ratios for spectral type since i n general the two hydrogen lines are of approximately equal intens i t y and similarly for the two helium singlets and the two t r i p l e t s . Since the process of reduction of intensity records i s so time-consuming i t i s natural to consider the p o s s i b i l i t y of taking readings of l i n e i n t e n s i t i es d i r e c t l y 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 l i n e 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 v i s u a l l y and by the use of suitable calibration the equivalent widths can be determined d i r e c t l y . The d i f f i c u l t i e s i n this method l i e i n the large variation i n width of the spectral lines being measured, the r e l a t i v e l y small depths of many of them, and the fact that the reading obtained i s not d i r e c t l y proportional to the equivalent width and behaves i n such a manner that the difference from proportionality varies with the shape of the l i 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 i n a spectrum with sharp lines,  a comparatively narrow s l i t can be used and the l i g h t 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 e a s i l y 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.  I f the maximum depth  of the center of the l i n e 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 l i n e 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 i n the method (plate grain, etc.) w i l l be related to the tcbal amount of l i g h t 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 f o r obtaining l i n e intensities for c l a s s i f i c a t i o n 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, Evans, J . W., Ap. J. ,__93_,  1918.  275, 1941.  Goldberg, Leo, Ap.J., §2, 623,  1939.  H i l t n e r , W. A., and Williams, R. C., Photometric Atlas of S t e l l a r  Spectra, Ann Arbor,1946. Morgan, W. W., Keenan, P. C. and Kellman, H., An Outline of S t e l l a r C l a s s i f i c a t i o n , i n An Atlas of S t e l l a r Spectra, Chicag  1943. Pearce, J . A., Pub.  D.A.0.,_5_,  No.  2, 1931.  J.R.A.S.C., 40, 139,  1946.  P e t r i e , 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.  

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