The Hat Creek millimeter-wave interferometer (to be known as the Berkeley-Illinois-Maryland Array, BIMA) is being upgraded. The improved array will become available during the coming solar maximum, and will have guaranteed time for solar observing. The Hat Creek millimeter-wave interferometer is described along with the improvements. The scientific objectives are briefly discussed

Gopalswamy, N.

Kundu, M. R.

Nitta, N.

Schmahl, E. J.

Welch, W. J.

White, S. M.

Breton 

NASA Technical Reports Server

N89- 1 5 8 6 3  
MILLIMETER WAVELENGTH OBSERVATIONS OF SOLAR FLARES FOR MAXI91 
M . R .  Kundu, N. Gopalswamy, N. Nitta, E . J .  Schmahl, S.M. White 
(U. Maryland) and W. J. Welch (U. C a l i f o r n i a ,  B e r k e l e y ) .  
B I M A  Arrav 
The Astronomy Program o f  t h e  Un ive r s i ty  o f  Maryland has  
r e c e n t l y  j o i n e d  the  U n i v e r s i t i e s  o f  C a l i f o r n i a  ( B e r k e l e y )  and 
I l l i n o i s  i n  a consort ium t o  upgrade t h e  Hat Creek mill imeter-wave 
i n t e r f e r o m e t e r  ( t o  be  known as  t h e  Berkeley-I l l inois-Maryland 
Array, o r  B I M A ) .  The improved array (see below) w i l l  become 
a v a i l a b l e  du r ing  t h e  coming So la r  Maximum, and we w i l l  have 
guaranteed time f o r  s o l a r  observ ing  as  par t  o f  t h e  consort ium. We 
p lan  t o  make quasi-dedicated o b s e r v a t i o n s  f o r  long  p e r i o d s  (10-15 
d a y s  a t  a t ime) ,  depending on s o l a r  a c t i v i t y .  
The Hat C r e e k  millimeter in t e r f e romete r  p r e s e n t l y  c o n s i 3 t s  o f  
three 6-m diameter an tennas  which  can b e  loca t ed  a t  v a r i o u s  
s t a t i o n s  a l o n g  a T-shaped road-way which ex tends  300 m East-West 
and 200 m North-South. Curren t  o p e r a t i o n  is in  t h e  2.5 - 4 mm 
wavelength atmospheric  window. The r e c e i v e r s  employ cooled 
Schot tky  d iode  mixers. The r e c e i v e r s  can  b e  tuned by a s o l i d  
s t a t e  o s c i l l a t o r  from 70 t o  115 GHz. Retuning t a k e s  about  5 - 15  
minutes .  Both s idebands  o f  t h e  f irst  mixer are received and are 
separated b y  phase swi t ch ing  o f  t h e  l o c a l  o s c i l l a t o r s .  Thus, two 
f r e q u e n c i e s  separated b y  2.3 GHz can b e  observed s imul t aneous ly .  
One l i n e a r  p o l a r i z a t i o n  I s  rece ived .  A quarter-wave p l a t e  t o  
produce c i rcu lar  p o l a r i z a t i o n  around 90 GHz is avai lable .  The 
r e c e i v e r ,  an t enna  and atmosphere c o n t r i b u t e  t o  the  the  s y s t e m  
tempera ture .  Scaled t o  above t h e  atmosphere,  t h e  temperature is 
t y p i c a l l y  300 t o  500 K SSB over most o f  t h e  band, r i s i n g  t o  about  
1000 K a t  1 15 GHz where t h e  o p a c i t y  is g r e a t e r .  
The BIMA consort ium has dec ided  t o  expand t h i s  i n t e r f e r o m e t e r  
i n t o  a 6-e lement  a r r a y  w i t h  15 b a s e l i n e s .  Work is a l r e a d y  i n  
p r o g r e s s  f o r  t h i s  expansion,  and i t  is expected t o  b e  complete i n  
2 years time. This ar ray  w i t h  1 5  b a s e l i n e s  w i l l  p e r m i t  u s  t o  
produce syn thes i zed  snapsho t  maps o f  s o l a r  f lares s imul t aneous ly  
a t  4 f r e q u e n c i e s  i n  t h e  range  70 - 240 GHz. Thus, no t  on ly  w i l l  
t h e  p o s i t i o n s  of  mm b u r s t  s o u r c e s  b e  known, bu t  t he i r  spectra w i l l  
a l s o  b e  determined w i t h  r easonab le  accuracy. Before t h i s  
expansion is completed,  however, we s h a l l  use the  ins t rument  a s  a 
3-element i n t e r f e r o m e t e r .  This  w i l l  b e  u s e f u l  t o  f i n d  t h e  
p o s i t i o n s  o f  s t r o n g e s t  b u r s t  s o u r c e s  w i t h  temporal  r e s o l u t i o n  
3 0.1 sec. 
f r equenc ie s  s e p a r a t e d  by  2.3 GHz. 
We s h a l l  b e  able t o  make these measurements a t  2 
107 
https://ntrs.nasa.gov/search.jsp?R=19890006492 2020-03-20T03:39:15+00:00Z
S c i e n c e  O b j e c t i v e s  
The millimeter r e g i o n  has  been p e r h a p s  t h e  most under-  
u t i l i z e d  o b s e r v i n g  wave leng th  r a n g e  i n  solar  p h y s i c s ,  due t o  t h e  
lack of t e l e s c o p e s  which c a n  match t h e  t e m p o r a l  and s p a t i a l  
r e s o l u t i o n  a v a i l a b l e  a t  o t h e r  wave leng ths .  Millimeter wave 
o b s e r v a t i o n s  are s e n s i t i v e  t o  b o t h  t h e  h i g h e s t - e n e r g y  e l e c t r o n s  i n  
f l a r e s  a s  well as  t o  c o o l  material i n  t h e  chromosphere.  
The s c i e n c e  we s h a l l  address d i v i d e s  n a t u r a l l y  i n t o  f l a r e s  
and  chromospher i c  s t r u c t u r e s .  Highly e n e r g e t i c  p a r t i c l e s  
accelerated i n  f la res  rad ia te  s t r o n g l y  a t  millimeter w a v e l e n g t h s :  
i n  p a r t i c u l a r ,  s i n c e  gamma-ray imaging is p r e s e n t l y  d i f f i c u l t ,  a 
millimeter array is t h e  o n l y  method o f  imaging t h e  most e n e r g e t i c  
p a r t i c l e s  i n  f l a r e s ,  and  we p ropose  many i m p o r t a n t  s t u d i e s  u s i n g  
t h i s  fact .  Using h i g h - t i m e - r e s o l u t i o n ,  we w i l l  s t u d y  pa r t i c l e  
a c c e l e r a t i o n  i n  t h e  i m p u l s i v e  phase ,  and  t h e  l o c a t i o n  o f  
a c c e l e r a t i o n  r e g i o n  i n  r e l a t i o n  t o  o t h e r  f l a r e  f e a t u r e s .  We hope 
t o  add g r e a t l y  t o  t h e  u n d e r s t a n d i n g  o f  prompt a c c e l e r a t i o n  i n  
f l a r e s  u s i n g  t e m p o r a l  and s p a t i a l  r e s o l u t i o n  p r e v i o u s l y  
u n a v a i l a b l e .  De lays  between gamma-ray and  millimter p e a k s  w i l l  b e  
s t u d i e d  i n  c o n j u n c t i o n  w i t h  s p a t i a l  i n f o r m a t i o n  on t h e  l o c a t i o n  of  
the millimeter sources, which ,  a long  w i t h  informat  ion i n  
microwaves,  w i l l  a l l o w  u s  t o  i n v e s t i g a g e  t h e  p r o p a g a t i o n  o f  e n e r g y  
from the  c o r o n a  t o  t h e  chromosphere d u r i n g  t h e  i m p u l s i v e  phase.  
And we w i l l  e s t a b l i s h  whether g a m a - r a y s  and mi l l ime te r -waves  come 
from i d e n t i c a l  r e g i o n s  b y  s t u d y i n g  t h e  a n i s o t r o p y  o f  millimeter- 
wave f lares on t h e  d i s k .  
O b s e r v a t i o n s  of s t r u c t u r e s  i n  t h e  chromosphere o u t s i d e  of 
f la res  w i l l  p l a c e  more emphas i s  on mapping, p a r t i c u l a r l y  of 
f i l a m e n t  d e p r e s s i o n s  and s h e a t h s ,  t h e  b r i g h t n e s s  d i 3 t r i b u t i o n  a t  
t h e  l i m b ,  a n d  o f  a c t i v e  r e g i o n  s t r u c t u r e .  Millimeter waves c a n  
i n v e s t i g a t e  t h e  i n t e r f a c e  between f i l a m e n t s  and t h e  c o r o n a ,  t h e  
u n d e r s t a n d i n g  of which is e s s e n t i a l  t o  model f i l a m e n t s .  We w i l l  
i d e n t i f y  f i n e  s t r u c t u r e s  which we e x p e c t  t o  f i n d  and r e l a t e  them 
t o  s p i c u l e s  and  i n t e r s p i c u l a r  r e g i o n s  i n f e r r e d  from l i m b  
b r i g h t n e s s  d i s t r  i b u t i o n s .  We w i l l  seek to  c o n f i r m  r e p o r t s  t h a t  
c o r o n a l  holes a p p e a r  b r i g h t  a t  millimeter wave leng ths ,  and s t u d y  
t h e  r e a s o n  for  t h i s .  Using mosa ic ing  t e c h n i q u e s  we w i l l  map 
a c t i v e  r e g i o n s  and s t u d y  t h e  c o r r e s p o n d e n c e  o f  o p t i c a l ,  
magnetogram and millimeter f e a t u r e s .  F i n a l l y ,  measurement o f  
c i r c u l a r  p o l a r i z a t i o n  w i l l  a l l o w  u s  t o  measure magne t i c  f i e l d s  i n  
t h e  chromosphere.  
108 
PATROL M O N I T O R I N G  OF THE S U N  AT M I L L I Y E T E R  WAVELENGTHS 
Aftor i t? e x t e n s i o n  t o  s ix -e l emen t s  t h e  B I M A  Array w i l l  
have a s e v e n t h  an tenna  a v a i l a b l e .  T h i s  a n t e n n a ,  a l r e a d y  
equipped w i t h  2-4 mm r e c e i v e r s ,  c a n  be used  f o r  m o n i t o r i n g  t h e  
Sun. I t  may be p o s s i b l e  t o  use t h i s  an tenna  f o r  f u l l y  d e d i c a t e d  
o b s e r v a t i o n s  o f  t h e  Sun a t  a number o f  o t h e r  wave leng ths ,  e . g .  2 
cm, 1 cm, 4mm and 2 mm. This arrangement  w i l l  p r o v i d e  u s  w i t h  
s p e c t r a  a t  h i g h  f r e q u e n c i e s  no t  a t  p r e s e n t  r o u t i n e l y  a v a i l a b l e .  
Da i ly  mon i to r ing  o f  s o l a r  continuum f l u x  a t  f o u r  
wave leng ths :  2 0 m m ,  10mm, 3 m m ,  and 1 .3mm.  The receiver-  is 
l o c a t e d  n e a r  t h e  v e r t e x  o f  a 6m diameter a n t e n n a ,  as shown i n  
F i g u r e s  4 and 5 below, f o r  two d i f f e r e n t  p o s s i b l e  r e s o l u t i o n s .  
I n  F i g u r e  4 t h e  r e c e i v e r  o b s e r v e s  t h e  e n t i r e  s u n  d i r e c t l y  w i t h  
l a r g e  beams a t  a l l  wavelengths .  In F i g u r e  5 m i r r o r s  are  
i n s e r t e d  so  t h a t  t h e  s u n  is observed w i t h  t h e  r e s o l u t i o n  o f  t h e  
6 m  a n t e n n a  (see t ab le ) .  Time r e s o l u t i o n  is > 0.1 sec, 
p e r m i t t i n g  t h e  s t u d y  of  f l a r e  development.  
- 
WAVELENGTH RESOLUTION 
2 -1 -
2 om 30 ' 12 ' 
1 om 30 ' 6 '  
3mm 3 0 '  2 '- 
1.3m 3 0  ' 1' 
109 
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FIG, 1, THREE ELEMENT INTERFEROMETER PRESENTLY 
A V A I L A B L E  FOR SOLAR OBSERVATIONS A T  M I L L I M E T E R  
( 2 - ~ M M )  WAVELENGTHS, THE ARRAY I S  SCHEDULED 
TO B E  COMPLETED BY EARLY 1991, 
110 
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FIG, 2,  A SCHEMATIC DIAGRAM OF THE S IX-ELEMENT 
BIMA ARRAY FOR M I L L I M E T E R  WAVELENGTH OBSERVATIONS 
OF THE S U N  (SEE T E X T ) ,  
1 1 1  
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c 
FIG,  3 .  THE SEVENTH ANTENNA OF THE BIMA ARRAY TO 
B E  USED FOR DEDICATED OBSERVATIONS OF SOLAR 
FLARES AT FOUR WAVELENGTHS I N  THE 20 - 1 , 3  MM 
RANGE, 
112 


Millimeter wavelength observations of solar flares for Max 1991

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