Oke, Greenstein, and Gunn (1966) called the GO star BD + 17° 4708 a field horizontal-branch star. They determined its effective temperature to be 6000° K, and its surface gravity as log g = 3.0. In his study of field horizontal-branch stars, Newell (1969) found + 17° 4708 to be the reddest such star, and it occupied a critical position in his plot of 0_e vs. log g, serving to separate more clearly the groups he calls disk horizontal-branch and halo horizontal-branch stars. It is the purpose ofthis note to indicate that + 17° 4708 is a G subdwarf, possibly slightly evolved, rather than a field horizontal-branch star

Cohen, Judith G.

Greenstein, Jesse L.

Caltech Authors - Main

1152 NOTES FROM OBSERVATORIES 
(1968). The data indicate that the visual magnitude of 3C 273 was 
rather erratic with a total variation of about 0.1 magnitude. 
Observations of 3C 273 for the years 1968 (Burkhead and Parvey 
1968), 1969 (Burkhead 1969), and 1970 (this note) are presented in 
Figure 1. The errors of the observations can be estimated by the 
standard deviations, a, of the comparison stars from their accepted 
photoelectric values. These standard deviations are 
(tv = ±0.017, aB-v = ±0.028, (Tu-b = ±0.04 . 
It should be noted that the (U—B) color indices observed at 
McDonald Observatory (1969, 1970) are more negative than those 
observed in Bloomington. The hour angle of the 3C 273 observa- 
tions at McDonald was large and there may be some difficulty in 
the reduction techniques. However, (U—B) color indices equaling 
those obtained at McDonald have been measured locally. It is 
therefore believed that these color variations are real. 
REFERENCES 
Burkhead, M. S. 1969, Pub. A.S.P. 81, 691. 
Burkhead, M. S., and Parvey, M. I. 1968, Pub. A.S.P. 80, 483. 
THE NATURE OF BD +17° 4708 
JUDITH G. COHEN AND JESSE L. GREENSTEIN 
Hale Observatories 
Carnegie Institution of Washington 
California Institute of Technology 
Received June 4,1970 
Oke, Greenstein, and Gunn (1966) called the GO star BD + 17° 4708 
a field horizontal-branch star. They determined its effective tem- 
perature to be 6000° K, and its surface gravity as log g = 3.0. In his 
study of field horizontal-branch stars, Newell (1969) found 
+ 17° 4708 to be the reddest such star, and it occupied a critical 
position in his plot of 0e vs. log g, serving to separate more clearly 
the groups he calls disk horizontal-branch and halo horizontal- 
branch stars. It is the purpose of this note to indicate that + 17° 4708 
is a G subdwarf, possibly slightly evolved, rather than a field 
horizontal-branch star. 
NOTES FROM OBSERVATORIES 1153 
The effective temperature of +17° 4708 was determined by two 
independent methods, one involving the profile of Hy and the 
other the slope of the continuum. Two calibrated spectra were 
available taken with the 200-inch Hale telescope on baked Ila-O 
plates with a dispersion of 9.0 Â mm-1. The Hy profiles were 
measured for each wing of the line on each plate and then averaged, 
to give the profile shown in Figure 1. Also shown in Figure 1 is an 
Hy profile from a radiative equilibrium, LTE model obtained from 
computer programs written by Dr. S. E. Strom, Mr. R. L. Kurucz, 
and Dr. D. M. Peterson. It is clear that the Hy profile for the 
model with Teff = 6250° K, log g = 4.0, and Z/Z0 = 0.1 satisfactorily 
matches the observed stellar profile. 
AX (A) 
Fig. 1 — Mean, reflected Hy profile in BD + 17° 4708. Circles represent ob- 
served profile; crosses, calculated profile at Teff = 6250° K, log g = 4.0, and 
one-tenth solar metal abundance. 
Several spectrophotometric scans of the star were kindly made 
available by Dr. J. B. Oke, and an average of these is shown in 
Figure 2, where we have used the absolute calibration determined 
by Oke and Schild (1970). Because the star is only moderately 
metal deficient, it is necessary to correct the observed scan for the 
effects of Tne blanketing. This had not been done by Oke, Green- 
stein, and Gunn (1966). Therefore the fraction of the flux removed 
by the lines of the appropriate wavelength ranges was measured on 
1154 NOTES FROM OBSERVATORIES 
Fig. 2 — Spectrophotometric scans of continuum by Dr. J. B. Oke. Observed 
points (filled circles) are corrected for blanketing and plotted as open circles. 
The solid line is the predicted flux for the model with logg = 4.0; the dashed 
line that for log g = 3.5. The points below the Balmer limit require the higher 
surface gravity. 
the two plates, and the observed scan was corrected as shown in 
Figure 2. The effective temperature determined from the scan, 
Tett = 6250° K, agrees with that from the Hy profile, and hence there 
is little interstellar reddening. The inclusion of line-blanketing 
corrections forces one to conclude that the surface gravity must be 
greater than log g = 3.0, and is probably about log g = 4.0. Thus the 
star is perhaps slightly evolved off the main sequence, which has a 
log g of 4.3 at this temperature. Unfortunately, our plates do not go 
below 3700 Â, so that we cannot correct the ultraviolet fluxes. 
Because the continuum is heavily obscured by lines, including the 
Balmer series, below 4000 Â the first few blanketing corrections are 
too small. The excess flux in the red is probably due to 1 ackwarm- 
ing. A similar effect in the red was observed with broad-band 
photometry by Johnson, MacArthur, and Mitchell (1968). 
NOTES FROM OBSERVATORIES 1155 
A second method of determining the surface gravity is through 
the use of the ionization equilibrium of iron. Equivalent widths of 
approximately 75 lines were measured and abundances were ob- 
tained using the method described in Cohen (1968). However, 
recent laboratory measurements of the gf values for Fei by Garz 
and Kock (1969) have revealed not only a change in the absolute 
normalization from the values of Corliss and Warner (1964), but 
also an error which depends on the excitation potential of the 
upper level of the lines. We have so corrected all the Fe i gf values, 
as a function of the excitation potential of the upper level. It is not 
yet clear whether a correction should be applied to the Fen 
transition probabilities, and hence we cannot use the ionization 
equilibrium of iron to accurately deduce the surface gravity. We 
find, however, that the observed equivalent widths yield abund- 
ances of Cri and Crn, of Tii and Tin, and of Fei (using new gf 
values) and Fen (using approximately scaled gf values) which are 
within 0.2 in the log of each other, when the model (6250, 4.0, 
0.1) is used. The star has an abundance of iron a factor of 10 lower 
than that of the sun; calcium, titanium, and magnesium appear to 
be deficient by a somewhat smaller factor, as often occurs in metal- 
poor stars. 
A further argument that T-17° 4708 is not a field horizontal-branch 
analog is based on its spatial velocities U, V, and W. The values 
given by Eggen (1964), assuming that the star is a GO subdwarf 
with My = 4.6, are ( + 252, —270, +43 km sec-1) respectively. 
If the star were a field horizontal-branch star, it would have My = 0.5 
to 1.5, and its space velocities would become incredibly large. 
One would then be surprised that the star is only moderately metal 
deficient, because of the high correlation of 8(U—B) with space 
motion. 
In résumé, we have redetermined the atmospheric parameters of 
the star BD +17° 4708. Evidence from a scan corrected for line 
blanketing, from the line spectrum, and from kinematic considera- 
tions, leads us to conclude that the star is a slightly evolved GO 
subdwarf, with a metal deficiency of approximately a factor of 10, 
rather than a field analog of the horizontal-branch stars in globular 
clusters. 
1156 NOTES FROM OBSERVATORIES 
We thank Professor Oke for the use of his scans, and for helpful 
discussion. We are grateful to Dr. Strom, Mr. Kurucz, and Dr. 
Peterson who wrote many of the computer programs used in this 
investigation. One of us (J.G.C.) gratefully acknowledges the 
support of a National Science Foundation traineeship. 
REFERENCES 
Cohen, J. G. 1968, Ap.J. 154, 179. 
Corliss, C. M., and Warner, B. 1964, Ap. J. Suppl. 8, 395. 
Eggen, O. J. 1964, Royal Obs. Bull No. 84. 
Garz, T., and Kock, M. 1969, Astr. and Ap. 2, 277. 
Johnson, H. L., MacArthur, J. W., and Mitchell, R. I. 1968, Ap. J. 152, 
465. 
Newell, E. B. 1969, Dissertation, Australian National University. 
Oke, J. B., Greenstein, J. L., and Gunn, J. 1966, in Stellar Evolution, R. F. 
Stein and A. G. W. Cameron, eds. (New York: Plenum Press), p. 399. 
Oke, J. B., and Schild, R. E. 1970, Ap.]. 161, 1015. 
NOTE ON THE LIGHT VARIATION OF 
GAMMA CORONAE BOREALIS 
R. TIPPETS AND S. K. WILCKEN 
Department of Physics and Astronomy 
Brigham Young University 
Received July 27,1970 
Percy (1970) has recently published some photometric observa- 
tions of y Coronae Borealis indicating a light amplitude of 0*^05 in 
yellow light in a period of approximately 0^03. Fernie (1969) had 
concluded earlier that the star may be a 8 Scuti variable of short 
period on the basis of 16 scattered observations. 
Observations of y CrB made in yellow light, relative to 0 CrB, 
were obtained on July 7 and July 12, 1970 with the 24-inch reflect- 
ing telescope of Brigham Young University. A refrigerated 1P21 
photomultiplier and five ten-second integrations per observation 
were used. The differential magnitudes in the sense of 6 CrB minus 
y CrB are displayed in Figure 1. Small differential magnitude cor- 
rections for atmospheric extinction have been applied to the data 
points. 


Nature of BD + 17° 4708

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Nature of BD + 17° 4708

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