Photoelectric photometry of star HD 11699

Chen, K.-Y.

English

NASA Technical Reports Server

.-. . 
. /  
PHOTOELECTRIC PHOTOMETRY OF HD 11 699 4* 
Kwan-Yu Chen 
Department of Physics and Astronomy 
University of Florida 
and 
** Cerro Tololo Inter-American Observatory 
+ * 
Contributions from the Cerro Tololo Inter-American Observatory, No. 000. 
** * 
Operated by the Association of Universities for Research in Astronomy, Inc., 
under contrast with the National Science Foundation. 
.3 
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https://ntrs.nasa.gov/search.jsp?R=19680004160 2020-03-12T11:42:25+00:00Z
. .  
ABSTRACT 
From observations on t h r e e  n ights ,  t h e  period of HD 116994 was found 
t o  be 0.1022623 day. 
c o l o r  curves.  The observed mean color i nd ices  are: B-V = M.393 and 
U-B = $0.137. The i n t r i n s i c  color i nd ices  are found t o  be: (B-V)o = 
4-0.270 and (U-B)o = 44.048. 
R = 1.4  Ro. The abso lu te  v i s u a l  magnitude is  estimated t o  be +2.0, which 
seems r e a l i s t i c  i n  view of t h e  i n t e r s t e l l a r  reddening and the pred ic t ions  
of t h e  pu l sa t ion  theory.  
Harmonic analyses were made of t h e  l i g h t  curves and 
Pulsa t ion  theory  y i e l d s  p 0.103 pa, a n d .  
r? 
'4' 
C 
.. 
I. INTRODUCTION 
The s t a r  HD 116994 (A5) = SA0 240869, i n i t i a l l y  chosen as a comparison 
s t a r  f o r  observing BV 513, was found t o  be a v a r i a b l e  a t  Cerro Tololo I n t e r -  
American Observatory on Apr i l  26-27, 1966. 
observed on t h e  following two nights and aga in  on May 2-3 with  HD 118014 
(AO) = SA0 240975 a s  t h e  comparison s ta r .  The apparent v i s u a l  magnitude 
It was then sys t ema t i ca l ly  
i s  l i s t e d  a s  8 . 7  f o r  both stars i n  t h e  Smithsonian Astrophysical Observatory 
S t a r  Catalog. 
IT.. OBSEXVAT'IONS AND W U C T I O N  OF DATA 
Observational da ta  i n  t h r e e  co lor - reg ions ,  uby, were obtained from a 
photometer wi th  standard UBV f i l t e r s  a t t ached  t o  t h e  No. 1 16-inch te lescope .  
An i n t e g r a t i n g  ampl i f i e r  was used, w i th  t h e  i n t e g r a t i n g  t i m e  set a t  20 sec. 
Each n i g h t ,  observations of t h e  comparison s tar  y ie lded  t h e  atmospheric 
e x t i n c t i o n  c o e f f i c i e n t s  and the  v a r i a t i o n s  of co lo r s  a s  l i n e a r  func t ions  
of a i r  mass. These va lues  were applied i n  t h e  reduct ion  of t h e  observed 
C! 
d a t a .  
and t h e  comparison s t a r ,  Am = m(var.) - m(comp.), co r rec t ed  f o r  d i f f e r e n t i a l  
The va lues  of t h e  d i f fe rence  i n  magnitude between t h e  v a r i a b l e  s ta r  
atmospheric e x t i n c t i o n ,  together w i th  t h e  t i m e  of v a r i a b l e  star obse<vation, 
a r e  l i s t e d  i n  Tables 1, 2 ,  and 3 f o r  y, b ,  and u r e spec t ive ly .  a 
Van den Bergh (1967) determined t h e  transformation equations t o  t h e  
UBV system f o r  t h e  observa t iona l  system used i n  h i s  photometry of g lobular  
C 
c l u s t e r s .  These equat ions ,  
. 
-2 - 
B-V = 0.998 (b-y) - 0.756 and 
U-B = 1.005 (u-b) - 0.985, 
were a l s o  used i n  t h i s  i nves t iga t ion ,  s ince  t h e  same observa t iona l  system 
was used by both au tho r s .  
v a r i a b l e  s t a r ,  cor rec ted  f o r  atmospheric e x t i n c t i o n ,  are l i s t e d  i n  Table 4 .  
The observed co lor  i n d i c e s ,  B-V and U-B, of t h e  
111. LIGHT AND COLOR VARIATIONS 
The v a r i a t i o n s  of Am, as wel l 'as  B-V and U-B, are p l o t t e d  i n  F igures  
1, 2 ,  and 3 ,  each of which i s  f o r  a d i f f e r e n t  day. The r e l a t i o n ,  
A m  = A. + C L n  1 A s i n  n(2nt/P1 + yn) + Bn s i n  n ( m t / P 2  + $,)I ~ 
n=l  
was used t o  analyze each l i g h t  curve. For convenience, t was chosen t o  be 
C 
, t h e  h e l i o c e n t r i c  J u l i a n  Date minus 2439243.0. The parameters, inc luding  
t h e  per iod ,  P, were determined by using an i t e r a t i o n a l  l ea s t - squa re  method, 
and t h e  r e s u l t  i s  l i s t e d  i n  Table 5. The v a r i a t i o n s  of t h e  co lor  i nd ices  
a r e  represented by a t runca ted  Fourier series, 
C [a cos (2mt /P )  + b s i n  (2mt /P) ]  , n n Ki=O 
where p i s  0,1022623 day, t h e  average value of P 
and t h e i r  probable e r r o r s  are l i s t e d  i n  Table 6. 
The c o e f f i c i e n t s  a and b 1' 
I V .  INTERSTELLAR REDDENING 
C; The discrepancy between the observed co lo r  index and t h e  Henry Draper  
s p e c t r a l  type of t h e  s ta r  suggests t h a t  t h e r e  is i n t e r s t e l l a r  absorp t ion .  
-3 - i 
.n . The i n t r i n s i c  co lor  i nd ices  of HD 116994 (4" = 297'20'.8, b1' = 11°10'.2) 
were obtained from t h c  r e l a t i o n  between t h e  co lor  d i f f e rence ,  Q, and t h e  
co lor  index, (B-V)o, i n  t h e  UBV system f o r  stars of luminosity c l a s s  V 
I 
I given by Beclcer (1963). The r e l a t i o n  between t h e  co lo r  excesses, 
was a l s o  used. The values obtained are: (B-V)O = M.270 and (U-B) = M.048. 
0 
This cons ide ra t ion  seems t o  give an upper l i m i t  f o r  t h e  co lo r  excess,  E = 
( B  -VI 
0.12. 
0 8  If KD 118014 (4" = 296 29 .7, bl' = 9'39l.6) i s  considered t o  be an 
AC? I1 s t a r ,  t h e  values (B-V)O = M.01, (U-B)o = (-0.06), and Q = (-0.07), 
given by Johnson (1958), can be applied.  The observed co lo r  i n d i c e s ,  B-V = 
$0.123 and U-B = -0.029, g ive  t h e  ca l cu la t ed  va lue  of -0.062 f o r  Q, which C 
for t h i s  s tar  i s  t h e  
(B -VI 
agrees  wi th  t h e  quoted va lue .  
same as t h a t  f o r  t h e  v a r i a b l e  s t a r .  
The va lue  of E 
Color i nd ices  of t hese  two s t a r s  are p l o t t e d  i n  F igure  4. 
V . DISCUSSION 
The period P determined i n  Sec. 111, may be considered t o  be t h e  1' 
per iod  of bas i c  o s c i l l a t i o n .  
mined from t h e  t h r e e  l i g h t  curves, a r e  very similar, although t h e  c o e f f i c i e n t s  
The t h r e e  values of P independently d e t e r -  2' 
f o r  t h e  terms involv ing  P a r e  small. Hence P i s  considered t o  be t h e  per iod  2 2 
of modulation. The r a t i o  of t he  f i r s t  overtone per iod  t o  t h e  fundamental 
per iod  i s  found t o  be 0.768, using t h e  average va lues  0.1022623 and 0.33826 
f o r  p1 and p 
w i t h  two periods given by Christy (1966), t h e  pu l sa t ion  cons tan t  of t h e  
r e spec t ive ly .  Comparing t h i s  w i th  t h e  shor t -per iod  va r i ab le s  (- .- 2' 
1. 
-4 - 
c 
fundamental mode, Qo, has a value of 0.0328. 
of the  mean dens i ty ,  p ,  of HD 116994 a s  0.103 pa. 
This e s t a b l i s h e s  t h e  value 
Using t h e  formula 
Qo 2 0.022 (R/Ra) 'l4(%/M) 1 /4 
of Chr i s ty ,  t h e  r a d i u s ,  R ,  i s  found t o  be 1.4 %, and t h e  mass, M, then  
would be 0.28 %, giv ing  a su r face  g r a v i t y ,  g, of 0.14 g o .  
Chr i s ty ' s  i n s t a b i l i t y  s t r i p  i n  t h e  log g d o g  T 
f o r  t h e  e f f e c t i v e  temperature, 
SO60 a t  log g = 3.59. 
Also, from 
plane,  t h e  boundary va lues  e 
a r e  found t o  be approximately 6500 and Te' 
Together wi th  t h e  r a d i u s ,  t h e  higher temperature 
gives MbOl = i-2.4, while t h e  lower temperature gives = i-3.4. 
McNamara (1965) gave t h e  r e l a t i o n  
= M.23 log  P + 0.473 (B-V)median 
f o r  dwarf Cepheids, fromwhich a value of 0.245 was obtained wi th  t h e  observed 
P1. The va lue  of (B-V) obtained i n  Sec. I V ,  agrees wi th  t h i s  computed 
(B -')med. 
v i s u a l  magnitude, 
0 '  
. I f  t h i s  v a r i a b l e  i s  considered t o  be dwarf Cepheid, t h e  absolute". 
can be  determined to be 3.4 from t h e  r e l a t i o n ,  
MV' 
M = - 3.33 log  P i- 2.96 (B-V) - 1.66 log (M/%) 4- 3.33 log Q + 3.34, 
V 
a l s o  given by McNamara. However, t h i s  abso lu t e  magnitude, combined wi th  
t h e  apparent magnitude and t h e  i n t e r s t e l l a r  absorp t ion ,  AV = 3 E (B-V) 9 gives 
a d i s t a n c e  of t h e  order of 100 parsecs.  It i s  d i f f i c u l t  t o  b e l i e v e  t h a t  
t h e r e  would be t h i s  amount of i n t e r s t e l l a r  absorp t ion  wi th in  such a d i s t ance .  
Unless t h e r e  i s  very l i t t l e  reddening of t h i s  s ta r ,  i t  i s  most probable 
t h a t  % = +2.0 which would place t h e  s ta r  a t  a d i s t ance  of 185 parsecs.  
L 
, 
-5 - 
The s i t u a t i o n  regard ing  reddening m i g h t  be r e a l i s t i c  i n  t h i s  case if it 
i s  compared with t h e  reg ion  of the Coalsack (AI' = 304O, bI1 = 0') , i n  
which t h e  photographic absorp t ion  ranges from 0.7 t o  2.4 a t  a d i s t ance  
of 174 parsecs (Rodgers 1960). Besides t h e  above problem wi th  t h e  absolu te  
magnitude and reddening i f  t h i s  s t a r  i s  considered t o  be a dwarf Cepheid, 
it i s  a l s o  pointed out  i n  t h e  l i t e r a t u r e  t h a t  t h e  amplitudes of t h e  l i g h t  
v a r i a t i o n s  i n  dwarf Cepheids are normally of t h e  order of 0.5 mag and 
l a r g e r ,  a s  compared with only 0.2 mag f o r  t h i s  s tar .  
4 
On t h e  o the r  hand, Danziger and Dickens (1967) gave da ta  f o r  s i x t e e n  
6 S c u t i  s t a r s ,  of which t h r e e  a r e  l i s t e d  as s p e c t r a l  type  A wi th  va lues  
of B-V of 0.25, 0.30, and 0.20. The a n a l y s i s  of t h e  l i g h t  curves of 
KD 116994 can a l s o  be compared w i t h  those  f o r  f i v e  6 S c u t i  s t a r s  repre- 
sen ted  by Leung and Wehlau (1967) i n  t h e  form, 
G 
Two po in t s  of d i f f e r e n c e  can be noted from t h e  comparison of t h e  c o e f f i -  
c i e n t s  i n  t h e  two i n v e s t i g a t i o n s :  
corresponding t o  t h e  period of basic o s c i l l a t i o n  are l a r g e r  f o r  HD 116994; 
and ( 2 ) ,  t h e  amplitudes corresponding t o  t h e  per iod  of modulation are much 
l a r g e r  f o r  t h e  6 S c u t i  s t a r s .  
(1) t h e  amplitudes of t h e  v a r i a t i o n s  
F i n a l l y ,  a comparison w i t h  p Pup (F6 IS), a 6 S c u t i  v a r i a b l e  wi th  
a period of 0.141 day, can be made. Ponsen (1963) inves t iga t ed  p Pup and 
found a near -s inusoida l  b lue  l i g h t  curve wi th  an  amplitude of 0.127 mag, 
and a (B-V) curve wi th  an  amplitude of 0.03 mag which i s  s i m i l a r  i n  shape 
t o  t h a t  of HI) 116994'. 
Ponsen found t h a t  i t s  indiv idua l  l i g h t  curves seem t o  show small systematic 
dev ia t ions  from t h e  mean curve.  Danziger and Kuhi (1966) found t h e  amplitude 
N o  secondary per iod  was found f o r  p Pup, although 
. of li&t v a r i a t i o n  (4566 A) t o  be 0.15 mag. 
and (B-V) i s  not apparent from t h e  comparison of t h e i r  0 curve with Ponsen's 
(B-V) curve. 
A l i n e a r  r e l a t i o n  between 8 r e 
e 
I n  view of t h e  l ack  of accurate spectroscopic work on HD 116994, t h e  
I 
I question of whether t h i s  s t a r  i s  a 6 S c u t i  v a r i a b l e  o r  a dwarf Cepheid cannot 
e 
be answered d e f i n i t e l y  a t  t h i s  time. 
s t a r  and p Pup, i t  i s  suggested tha t  HD 116994 could be a counterpar t  of 
p Pup but of e a r l i e r  s p e c t r a l  type.  
However, from t h e  s i m i l a r i t y  of t h i s  
- 
I n  t h i s  ca se ,  t h e  abso lu te  magnitude 
of HD 116994 might w e l l  be of the order of 4-0.5, which g ives  a d i s t ance  
o f  370 parsecs.  This would probably account s u c c e s s f u l l y  f o r  t h e  reddening, 
b u t ,  l i k e  p Pup, i t  would no t  f i t  n e a t l y  i n  t h e  p i c t u r e  of present  pu l sa t ion  
theory .  
The author would l i k e  t o  thank D r .  A .  G. Smith, then Acting Direc tor  
of Cerro Tolo lo  Inter-American Observatory, f o r  h i s  encouragement and support  
of t h i s  i n v e s t i g a t i o n .  The a s s i s t ance  rendered by h i s  s t a f f  both on t h e  
mountain and i n  La Serena are very much apprec ia ted .  
g r a t e f u l  t o  D r .  F.  B. Wood f o r  supplying l i b r a r y  ma te r i a l  t o  i d e n t i f y  t h e  
The author i s  a l s o  
. I  
v a r i a b l e ,  t o  D r .  S .  van den Bergh f o r  sending h i s  manuscript p r i o r  t o  i t s  
pub l i ca t ion ,  and t o  D r .  R .  B. Carr f o r  h i s  a s s i s t a n c e  i n  using t h e  IBM 709 
computer. 
This work could not have been done without t h e  f i n a n c i a l  support of 
t h e  Nat iona l  Aeronautics and Space Administration and t h e  National Science 
Foundation. Their a s s i s t a n c e  i s  g r e a t l y  apprec ia ted .  
. -7 - 
REFERENCES 
Becker, W .  1963, Basic AsCronomical Data, ed. K.  Aa. Strand (Chicago: 
Univers i ty  of Chicago P r e s s ) ,  p p .  241-261. 
c 
Bergh, S .  van den 1967, A .  J .  72, 70-81. 
Chr i s ty ,  R .  F .  1966, Annual Review of  Astronomy and 'Astrophysics Vol. 4, 
e\ 
ed .  L .  Goldberg (Palo Alto:  Annual Reviews, Inc .) , pp.  353-392. 
Danziger, I. F .  and Dickens, R .  F .  1967, Ap. 3 .  1A9, 55-72. 
Danziger, I .  F .  and Kuhi, L .  V .  1966, Ap. J .  z, 743-747. 
Johnson, H. L .  1958, Lowell Obs. B u l l . p i ,  37-46. 
Leung, K-C. and Wehlau, W .  1967, A p .  J .  9, 39-46. 
McNamara, D .  H .  1965, K 1 .  V e r .  Barnberg 5, 11'1-122 (No. 40). 
Ponsen, J.  1963, B .  A .  N .  17, 44-52. 
Rodgers, A .  W .  1960, M. N .  120, 163-172. 
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. '  
FIGURE LEGENDS I 
. -  
Fig .  1 Light and co lor  va r i a t ions  of HD 116994 on A p r i l  27-28, 1966, 
with computed curves.  
Fig.  2 Light and co lo r  va r i a t ions  of HD 116994 on A p r i l  28-29, 1966, 
with computed curves ,  
F i g .  3 Light and co lo r  va r i a t ions  of HD 116994 on May 2-3, 1966, wi th  
computed curves.  
F ig .  4 P l o t  of observed co lor  indices  of HD 116994 and HD 118014; 
dashed l i n e s  i n d i c a t e  the reddening l i n e s ,  and t h e  dot ted  
curve is  t h e  computed path of t h e  v a r i a t i o n s  of co lor  i nd ices  
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8 


Photoelectric photometry of HD 116994

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