PUBLICATIONS OF THE DAVID DUNLAP OBSERVATORY UNIVERSITY OF TORONTO
Volume II Number 18
ABSOLUTE ENERGY DISTRIBUTIONS FOR STARS OF SPECTRAL TYPES F, G AND K
GRETCHEX L. HAGEN AXD SIDNEY VAN DEX BERGH
1967 rORONTO, CANADA PRINTED AT THE UNIVERSITY OF TORONTO PRESS ABSOLUTE ENERGY DISTRIBUTION'S FOR STARS OF SPECTRAL TYPES F, G AND K
By Gretchen L. Hagen and Sidney van den Bergh
Abstract
Absolute energy distributions over the range 3600 < X < 4500 A. are given for 154 stars of spectral types F, G and K. The spectral energy distributions of these stars are compared to those of globular clusters and galaxies. Globular clusters are found to resemble metal-poor high-velocity stars. The spectral energy distributions of the nuclei of M31 and M32 are obviously composite. M32 appears to be either dwarf-enriched or moderately metal-poor.
The observations reported in this paper were obtained with a spectrum scanner which is located at the Cassegrain focus of the
74-inch telescope. The dispersing element of this instrument is a Bausch and Lomb replica reflection grating with 600 grooves per millimetre. The centre of its blaze is at X3750 in the second order, which was the order used. A refrigerated 1P21 photomultiplier was employed as a light detector. Tracings of a large number of stars covering the range 3600 < X < 4500 A. were available from previous observing programmes (van den Bergh 1963, 1966, and van den Bergh and Sackmann 196.")). All tracings were made at an effective resolution (spectral purity) of 20 A. Observations of early-type standard stars (Oke 1960) were used to transform the observed deflections to absolute energy units. The mean wave-length-dependence of atmospheric extinction was taken from van den Bergh and Henry (1962). It should be emphasized that the observations used for the present programme were originally made to measure narrow-band parameters. Such measurements do not require nights of the highest photometric quality. The accuracy of the results is therefore lower than that which could have been obtained in a programme devoted exclusively to studies of the spectral energy distributions of stars. The present study includes only those stars for which at least four tracings obtained during two or more nights were available. The average internal mean error of the combined data for each star is found to be 0.02 mag. at X4000, 0.03 mag. at X3800 and 0.04 mag. at X3600. Within the accuracy of the data these errors are found to be independent of apparent magnitude and spectral type.
470 480 Grctchen L. Hagen and Sidney van den Bergh
F6 ^ Absolute Energy Distributions 481
Typical tracings of stars are shown in figures 1 and 2 where the dashed line represents the adopted schematic continuum. Except near the G-band and the H7 and H<5 lines the adopted schematic continuum in the region X > 4000 A. coincides with the observed pseudo-con- tinuum. For X < 4000 A. the adopted schematic continuum represents the strongly smoothed mean of the actually observed pseudo-con- tinuum. The only reason for drawing the schematic continuum in this particular fashion is that it yields consistent and easily reproducible results.
For all of the programme stars the observed values of m(\ X), at
100 A. intervals along the schematic continuum, are given in Table I. In the table n is the number of tracings on which the tabulated values of ra(l/X) are based. Stars whose H.D. numbers are marked with an asterisk have spectral types which were determined by Mr. Peter Hagen using 74-inch spectra having dispersions of 33, 40 or GO A. mm. The spectral types for H.D. 208110 and H.D. 22211 are uncertain.* Figures 3 and 4 show sample plots of the schematic spectral energy distributions of stars of different spectral types and luminosity classes.
The data in Table I may be used to form monochromatic colour indices. For example a monochromatic colour index C(41-4o) can be defined by the equation
C(41-4f)) = w(l X)(4100) - m{\ 'A)(4500).
Figure 5 shows a plot of the observations of the colour index C(41-45) versus C(38-45) for main sequence stars (dots) and subgiants (crosses). Binaries and metal-poor stars with ultraviolet excess 8(U-B) > 0.10 have not been plotted. Figure G shows that such metal-poor stars
(dots) lie above the monochromatic colour-colour curve for stars of normal metal abundance. Using the wave-length dependence of interstellar reddening given by Whitford (1958) and the globular cluster reddening values given by van den Bergh (1967) it is possible to obtain the monochromatic intrinsic colour indices of globular clusters (\an den Bergh and I [enry
H.D.208110. Peter Hagen classifies this star as (i() IV, MI with the following comments: (1) the star rotates very slowly. (2) the standards available .it D.D.O. in this region are not complete. (3) Sr II (X4077) is very sharp and indicates a much higher luminosity than given by other criteria. (4) Ca II (X4227) gives an earlier spectral class than do the II lino.
I I.I ). 22211. The spectral type is uncertain because all the lines appear to lie rotationallj broadened to an extent which may be inconsistent with the classification of t".u III. 482 Gretchen L. Hagen and Sidney van den Bergh
1962). In figure 6 the intrinsic colours so obtained are plotted as crosses. The figure shows that globular clusters fall in the same region of the monochromatic two-colour diagram as do high-velocity stars.
Monochromatic intrinsic colours of the nuclear regions of A 1 31 and M32 were derived by assuming a reddening EB-v = 0.12. The
positions of A 1 31 and A 1 32 in figure 6 suggest that their spectral energy
3600 3800 4000 4200 4400 \
Fig. 3—Comparison of the absolute energy distributions of the following main sequence stars: H.D. 58946 (FO), H.D.34411 (GO) and H.D.75732 (KO). Absolute Energy Distributions is:; distributions are composite. Table II shows that the combination GO Y + K2 III (with the G star contributing one third of the light at A4500) gives a reasonably good representation of the spectral energy distribution of the nucleus of M31 over the range 3600 < X < 4500 A.
It should be emphasized that this type of synthesis is not unique. Nevertheless the data suggest that stars near the main-sequence turn-oft
3600 3800 4000 4200 4400 \
Fig. 4—Comparison of the absolute energy distributions of H.D.20630 (('.-"> Y and H.D.27022 (Go III). 484 Gretchen L. Hagen and Sidney van den Bergh
0.5 Absolute Energy Distributions 485
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486 Gretchen L. Hagen and Sidney van den Hergh
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X l~ 3 3. -T 3 01 OI — CD COCO '0 t- X 3. 3: 3. — l> OI 1^ Tf ~ c3 — ro ro _ 3. -r 3 -r 3. -tozt- t -t O. L7 C ro CD I- 3 3. — 3 X — t- ~ ~f ir. y_ — CO 3- 01 — -T i0 rO X 3. 01 01 01 -t iO C3 CD t^ X 3 3 ro CD I- I- 3. XX CD — "O iO 1^ t~ 3. -T 'O SCNNN X X'00 00 OC X X X X 3. 3. 3. 3. 3 3. 3. 3 3 3 3; — — 01 OI _ „ „ ^ „ _ „ _^ „ „ —OIOIOIOI O101010101 01010101 Absolute Energy Distributions 491 TABLE II Comparison of the intrinsic spectral energy distribution of the nucleus of M31 with a composite of H.D.109358 = /3 CYn (GO V) and H.D. 140573 = a Ser (K2 III). In the model one third of the light at 4500 A. is contributed by dwarfs. X 492 Gretchen L. Hagen and Sidney van den Bergh strengths in M31 and M32 it may be necessary to assume that some of the giants in the nucleus of M32 are metal-poor objects in which CX is weak. Some of the tracings used in this investigation were obtained by are also due Inge J. Sackmann, W. E. Greig and R. C. Henry. Thanks for classifications of a number of to J. Peter Hagen, Jr. providing MK programme stars. Generous financial support was provided by the .National Research Council, Ottawa. References Bergh, S. van den. 1963, Astron. J., vol. 68, 413; 1966, "Spectral Classification and Multi-colour Photometry," I.A.I". Symposium Xo. 24. (Academic Press, London) p. L32; 1967, Astron. J., vol. 72 (in press). Bergh, S. van den and Henry, R. C. 1962, D.D.O.Pub., vol. 2, 281, no. 10. Bergh, S. van den and Sackmann, I. J. 1965, Astron. J., vol. 70, 353. Oke, J. B. I960, Ap. J., vol. 131, 358. Whitford, A. E. 1958, Astron. J., vol. 63, 201.