Ground based photometry of potential navigation guide star

Courten, H. C.

Smith, L. L.

English

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https://ntrs.nasa.gov/search.jsp?R=19700001714 2020-03-12T04:56:21+00:00Z
IRM-430
GROUND BASED PHO'T'OMETRY OF
POTENTIAL NAVIGATION
GUIDE STARS
November 1968
--T -A1--V —AF• 11 — -S,w^a '- ^ a 7 --a J -
0 N70 -11 0 18
_	 (ACCt£SION NUMBER)
	 (TMRUI
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16 6, - lo (6 76)
(NASA CR C R TMX OR AD NUMUER)
	 (CATEGORY)
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1
I
1
ACKNOWLEDGMENTS
The authors wish to thank Mr. Lawrence T. Draper of the
Goddard Space Flight Center, National Aeronautics and Space
Administration; and Dr. Harold L. Johnson, Mr. Richard I. Mitchell,
and Mr. David Steinmetz of the Lunar and Planetary Laboratory,
University of Arizona, for their valuable assistance in this
project.
ii
ABSTRACT
There is a current need in space astronomy to calibrate ac-
curately the magnitude of the brighter stars used as navigation
guide stars in unfiltered tracking systems. In the past, these
magnitudes have always been computed from observed narrow-band
data, because there have been few direct observations with these
systems.
Photoelectric observations of bright stars have been made
using the Lunar and Planetary Laboratory 21-inch telescope and a
calibrated 1P21 phototube, unfiltered. The magnitude observed is
designated [m(S-4)] to indicate that an (S-4) photosurface
(1P21 phototube) was used. Calibration curves of [m(S-4) - V]
versus (B-V) were derived separately for the supergiant, giant,
and subgiant stars, where B and V are the blue and visual
photoelectric magnitudes. The curves for the supergiants and
giants in the region +0.1 < (B-V) < +1.2 are similar and quite
linear, while they differ by A[m(S-4) - V] ! 0.15 mag for
-0.3 < (B-V) < +0.1. Theoretical investigations show that the
(S-4) magnitude of a given star will vary for different 1P21
phototubes. It is concluded that calibration curves must be de-
rived separately for stars of different luminosity classes for
each detector system of interest.
A preliminary investigation has confirmed the validity of
both the Goddard Space Flight Center m(S-4) computer program
and the OAO-A2 guide star list.
iii
TABLE OF CONTENTS
Item	 Pie
Introduction ............................................... 	 1
Discussion ................................................. 	 2
Conclusions ................................................ 	 7
References ................................................. 	 S
iv
INTRODUCTION
There is a current need in
bration curves for the brighter
detector system. To date a few
star trackers on Aerobee rocket
veyor, and Orbiter spacecraft.
for broad-band systems, such as
space astronomy for stellar cali-
navigational stars in terms of the
stars have been observed by using
flights, and on the Mariner, Sur-
In the past, the calibration curves
an unfiltered 1P21 phototube, have
been computed from observational filter-band data. In order to
check these theoretical calculations, an observational photometric
program was attempted at a high altitude observatory using a cali-
brated 1P21 phototube. A preliminary report has already been pub-
lished (Ref. 1.). A complete reduction of all the data is given
in the present report.
i
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1
DISCUSSION
Photoelectric observations on stars brighter than 3.0 visual
magnitude (V) were obtained using the 21-inch telescope of the
Lunar and Planetary Laboratory, University of Arizona, in May and
October 1967. Because of the relatively poor observing conditions
in May, which were evidenced by large atmospheric extinction values,
only the October data is considered here.
Thirty stars were measured on the nights of October 12/13,
14/15, 15/16, and 1.6/17, 1967, using an unrefrigerated 1P21 photo-
multiplier tube (HR 145) operated at 700 volts. No filter_ was
used, and the field of view at the telescope focal plane was dia-
phragmed to one minute of arc. The phototube spectral response
was measured with the NBS Photodetector Spectral Response Console
at Grumman Aircraft Engineering Corporation on September 18, 1967.
This response is presented in Table I and includes the effect of
the two aluminum-coated telescope mirrors.
The standard operating procedure was to observe star plus
sky for 15 seconds, then sky for 15 seconds, and to repeat the
observations at least twice. A calibration lamp was observed for
each star observation to monitor the absolute sensitivity of the
system, and all data were recorded automatically on punch tape.
The time at both the beginning and end of each observation was
recorded, as were the amplifier gains. The magnitude observed is
designated [m(S-4)] to indicate that an (S-4) photosurface
(1P21 phototube) was used. The magnitude for a given star ob-
served through air mass X can be written as:
_	
25 10	
(Isr_ar+sky - Isky)	 (1)[m(S-4) ]X __ (star	 lamp ) - . g10	 (I	 - I	 )lamp dark
where
1
1
1
1
1
1	 2
Gstar is the gain used for the star measurement,
Glamp is the gain used for the calibration lamp
Imeasurement,
Tst-ar+sky is	 the measured intensity of the star+sky,
I is	 the measured intensity of the sky alone,
sky
Ilamp is the measured intensity of the calibration
' lamp, and
I(lark is the measured intensity of the dark current.
The stellar magnitude at the top of the atmosphere is given
by
I
	 [m(S-4)]0 = [ m ( S -4 )] X - k (S-4) X 	 (2)
where k (S-4) is the total atmospheric extinction coefficient.
The air mass X is given by
X = sec Z - 0.00.18167(sec Z-1) - 0.0028%5(sec Z-1)2
(3)
- 0.0008083(sec Z-1)3
and
sec Z = (sin q) sin 5 + cos ^p cos 5 cos h)- 1 	 (4)
where
D^	 is the latitude of the telescope (32° ?5' 0'.8 N),
s	 is the declination of the star, and
h	 is the hour angle of the star at the time of observation.
The expression for the air mass, Eq. (3), comes from Hardie
'	 (Ref. 2). It agrees with the expressions used by Young and Irvine
(Ref. 3) and Mitchell (private communication) to within 0.01 for
I3
X < 3.0	 anti to within
	
0.02
	 for	 X < 4.0.	 A given star is ob-
served at different air masses and a least-squares fit is made to
Eq.	 (2)	 to derive	 k(S-4)'	 Figure 1 presents the results 	 for the
night of October 12/13,
	
1967, where the values of
	 k	 ,	 de-(S-4)
termined for
	 19 stars, are plotted against the
	 (U-B)
	
color
(Ref.
	 4).	 The	 (U-B)	 color was used as the abscissa rather than
(B-V)	 in order to achieve a smoother relation.	 The quantities
U,	 B,	 and	 V	 are the ultraviolet, blue, and visual photoelectric
magnitudes.
	 The curve in Fig.
	 1 represents the mean extinction
for the night, and is used to derive
	
k (S-4)	 values for these
' stars either observed only once or with poorly determined extinc-
tion values.
	 It can be seen that 	 k (S-4)	 varies smoothly with
stellar color, and reaches a maximum value of
	 0.32	 for stars of
earliest spectral class
	 [(U-B) ti -1.01.
1 The zero point for the	 (S-4)	 magnitude system,	 [m(S-4)]= 0,
is defined for
	 ry. Lyrae	 (Vega).	 Values of	 (m(S-4)] 0	are deter-
, mined separately for each night, and a final mean value, weighted
by the number of nightly observations,
	
is calculated.	 Table II
presents the results for the
	
30 stars observed in October 1967.
The stars are listed by their bright star numbers
	 (B.S.)	 given
in Ref.	 5.	 The weighted probable errors
	 (p.e.)	 are also given,
along with the total number of observations
	
(n)	 for each star.
The mean probable error is
	
±0.01 mag,	 with the maximum being
±0.03 mag.	 Three stars
	 (B.S.	 1017,	 2294, and 2491)	 were ob-
served on only one night, and the
	 p.e.	 values are estimated as
an upper limit.
	 The	 UBV	 and spectral classification	 (Sp)	 data
lare from Johnson et al.
	 (Ref. 4) .
A color index [m(S-4) - V] is now derived for each star.
Figure 2 shows the observed stellar calibration curves for super-
giants (Ia, b), giants (II and III), and subgiants (IV and V);
1
4
11
the data was obtained by using an ui , filte.id 1P21 photomultiplier
tube (HR 143). The supergiants and giants foli-, the same linear
curve in the region +0.1 < (B-V) < +1.2. This is not surprising
since the effective wavelengths of [m(S-4)] and the B magnitude
are within 200 ^ of each other. The subgiant stars in the region
+0.1 < (B-V) < +0.5 are brighter in the ultraviolet (a < 3650 ^)
than the supergiants, and this results in a more negative (bluer)
color index [m(S -4) - V], that places the subgiant curve above
the supergiant curve. This situation is reversed in the region
-0.3 < (B-V) < +0.1, where the subgiant and giant stars are
fainter than the superglants in the ultraviolet. This produces
it separation between the two curves of ii[m(S-4) - V] = 0.15 mag
for a given (B-V).
It should be mentioned that the data of Fig. 2 have not been
corrected for the effect of interstellar reddening. As most super-
giants and giants are reddened to some degree, the calibration
curves should be considered as only approximate in the region
-0.3 < (B-V) < +0.1. A highly reddened star with observed (B-V)
-0.1 will not have the same [m(S-4) - V1 value as an unreddened
star with the same value of (B-V). Space reddening has little
effect on the stars in the region +0.1 < (B-NI) < 4. 1.2 as evi-
denced by linearity of the calibration curve.
The photomultiplier tube used in this study to obtain the
stellar data has a "blue shifted" spectral response relative to
normal 1P21 phototubes. dalculations made using the measured
stellar energy distributions of Kharitonov (Ref. 6) and Kharitonov
and t,nyazeva (Ref. 7) have indicated that Lhe bluest stars will
appear up to 0.15 mag brighter, and the reddest stars 0.20 mag
fainter when observed with phototubes with a "normal." response than
when observed with the "blue shifted" phot6tube H':: 145. (The zero
point for all magnitude systems is normalized to a Lyrae.) These
1
1
I
1
1
1
1
1
1
	 5
rmagnitude differences should be considered as only approximate, be-
cause extremely "rect shifted" or "blue shifted" 1P21 tubes will
produce even larger magnitude differences when compared to "normal"
1P21's (L. Draper, private communication).
A preliminary investigation, using the observed data in the
present report and Kharitonov's measured stellar curves, has shown
that all of the stars in the OAO-A2 guide star list are indeed
brighter than 2.0 mag [m(S-4)] for every OAO star tracker. This
is the spe;ified guide star limiting magnitude. While this does
not preclude the addition of a few more stars, it does confirm the
validity of the Goddard Space Flight Center [m(S-4)] computer
program.
6
CONCLUSIONS
It is concluded that the conversion between magnitude systems
such as the UBV and [m(S -41 systems must be handled with care.
The calibration must be obtained either by direct observation or
from theoretical. considerations for each detector system of inter-
est. The differences between the spectral responses in a given
generic family of phototubes can produce magnitude differences of
up to several tenths for a given star. A calibration curve must
be derived separately for the supergiant, giant, and subgiant stars,
as differences of up to 0.15 mag can exist between these stars for
a given (B-V).
7
1
1
I
REFERENCES
1.	 Smith, L. L. and Courten, H. C., "Bright Star Observations
Using an Unfiltered 1P21 Ph ototube," Grumman Research Depart-
ment Memorandum RM-406J, February 1963; Abstract published
in Astron. J., Vol. 73, p. S35, 1968.
"Photoelectric Reductions," in2 .	 Hardie, R. H. ,Stars and_
Stellar_ Systems, Vol. II; Astronomical Techniques, ed. by
	
1	 W. A. Hiltner, The University of Chicago Press, Chicago,Illinois, 1962.
3.	 Young, A. T. and Irvine, W. M., "Multicolor Photoelectric
Photometry of the Brighter Planets. I. Program and Procedure,"
Astron. J., Vol. 72, p. 945, 1967.
	
'	 4	 Johnson H. L. Mitchell K. I. Iriate. B. and Wisniewski
W. Z., "UBVRIJ KL Photometry of the Bright Stars," Communications
	
1	 of the Lunar and Planetary Laboratory, Vol. 4, No. 63, p. 99, 1966.
5. Hof f left, D., Catalogue & 6r- LIIL Stars, Yale University Observa-
tory, New Haven, Connecticut, 1.964.
6. Kharitonov, A. V., "Extra-Atmospheric Spectrophotometric
	
'	 Standards," Sov. Astron - A. J.
-
, Vol. 7, p. 258, 1963.
7. Kharitonov, A. V. and Knyazeva, L. N., "Absolute Spectral Energy
Distribution for 10 Type B5-M2 Stars," Sov. Astron - A. J.,
Vol. 11 2 p. 598, 1963.
1
1	
9
1
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iiii
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Table I
SPECTRAL RESPONSE DATA FOR
PROGRAM 1P21 _PHOTOTUBE JHR 1.45
T(A)
P
^\(,`	 ) Rt
3000 0 56 58.7
31 5.9 57 51.1
32 19.6 58 43.6
33 32.5 59 31.1
34 44.7 6000 17.7
35 56.1. 61 9.2
36 66.4 62 4.8
37 75.4 63 2.8
38 82.2 64 1.6
39 88.3 65 1.1
4000 93.1 66 0.7
41 96.8 67 0.4
42 98.2 68 0.2
43 99.2 69 0.2
44 100.0 7000 0.1
45 99.9 71 0.1
46 99.4 72 0
47 98.4 73 0
48 97.0 74 0
49 95.4 75 0
5000 94.2
51 91.8
52 87.5
53 81.2
54 73.8
55 66.2
tResponse includes effect of two aluminum-coated telescope mirrors.
9
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PQ	 44 ,e :4 u AQ =	 U W GO	 ^ < w x ^4
r- M O^ OCR N U'1 Lr) 00 Q1 1-- N ^O Url In r-1 M "t 00
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.	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .
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1	 i	 1	 1	 1	 I	 1
r-1 't o0 O -,t O M N M N oo ^ O O -t N ^ N
r-1	 ^o In 00 O N r-4 00 r-I N O O O -,t r-4 ir1
.	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .
O	 G	 O O O O O O O O O O O ^-+
1	 1	 1	 I	 1	 1
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N N H N O O O H r--I N N	 '" ' * O N N
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00 Lr) r--I Cr OG In O r-4 00 Lr) Lr) In Lr) N N
r-4 M N M rl O O 1 r--1 M r1 e-a r--I r-a 1-1 O M M -r4
@ 1 1J
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Q H p4 H pG F-i H : Pa J-4 H x S-+
x w w u 114 wa w FQ-+ ¢ o o H O U C7 U C7 U O Q v
a a a aa a a a w w w w w^ ¢ ¢ u ¢ ¢ pq u as as u <^ ¢ ¢ pa c7
^4Ur1 r-1 r- r-4 rte. 00 M O r+ 0,1% -t r-I r-+ O cr1 M Lr) O
r-1 r-I r-1 M Ifl O r-1 O1 CT N O ON N ON CT ^t O O pO'N O N ^t r^ t\ r- r- Oo O N -t -,t 00 O\ % D r- ( a
r-I r-1 r-I r--I "-4 r--1 r-1 rl N N N N N N ^ ^,C +-
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Ground based photometry of potential navigation guide stars

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