Page   1
    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID 3608c
                                                       Report Date: 09-May-96:18:45
                                                       Version: **********
                                                       Check-in Date: **********

1.Proposal Title:
THE 12C TO 13C ISOTOPE RATIO IN PLANETARY NEBULAE
------------------------------------------------------------------------------------
2. Scientific Category   3. Proposal For  4. Proposal Type        5. Continuation ID
INTERSTELLAR MEDIUM         GO                                       <none>
Sub Category
PLANETARY NEBULAE
------------------------------------------------------------------------------------
6. Principal Investigator   Institution                    Country    Telephone
 Robin Es Clegg             ROYAL GREENWICH OBSERVATORY    UK         +44-223-374700

------------------------------------------------------------------------------------
7. Abstract
Abundances of C,N and O in red giant stars and planetary nebulae (PNs) provide
important diagnostics of stellar evolution theory. CNO isotope ratios (eg 12C/13C,
15N/14N and 16O/18O) have given many extra constraints on all the mixing processes
occurring between the main sequence and PN ejection. In general, observations show
more mixing occurs than is predicted. The CNO abundances for Galactic and Magellanic
Cloud PNs show that the `3rd dredge-up' of 12C is more efficient in metal-poor
environments. However, until now it has not been possible to measure important
diagnostics such as the 12C/13C ratio in nebulae so as to relate red giant & PN
populations. We propose to use the GHRS, Echelle and Large Science Aperture to
measure C12/13 ratios in 3 PNs with a novel spectroscopic method. As 12C has zero
nuclear spin, the normal C III 1S(J=F=0) - 3P(J=F=0,1,2) transition has only two
components (1906.7, 1908.7A). But the nuclear spin (I=1/2) of 13C gives a finite
line strength to an F=1/2-1/2 transition at 1909.6A, which is absent in 12C.
Measurement of all three lines will provide the C12/13 ratio. In an allocation of
under 9 hours we can reach 3-4 sigma limits for a C-rich Galactic nebula, a C-rich
SMC nebula, and a Type I (He and N-rich, and having C<O) PN in the LMC. We can
measure to limiting isotope ratios between 30 and 90. Our LMC Type I target is
probably descended from the group of N-rich M/MS/S stars, found by Smith & Lambert
to have 12C/13C ratios between 5 and 30.
------------------------------------------------------------------------------------
------------------------------------------------------------------------------------
9. Est obs time (hours) pri: 5.53     par: 0       10. Num targs pri: 3      par: 0
------------------------------------------------------------------------------------
11. Instruments requested:  HRS
------------------------------------------------------------------------------------
------------------------------------------------------------------------------------
                                                                  Page   2
I. GENERAL FORM    Proposal 3608c
PI:  Robin Es Clegg
Proposal Title:
THE 12C TO 13C ISOTOPE RATIO IN PLANETARY NEBULAE
------------------------------------------------------------------------------------

1. Proposers:
Proposers                        Institution                       Country       ESA
------------------------------------------------------------------------------------
Pi Robin Es Clegg                ROYAL GREENWICH OBSERVATORY       ENGLAND        X
 Peter J Storey                  UNIVERSITY COLLEGE LONDON         ENGLAND        X
 Jeremy R Walsh                  SPACE TELESCOPE EUROPEAN          GERMANY        X
                                 COORDINATING FACILITY
------------------------------------------------------------------------------------
  3. Description of proposed observations.
  The 12C/13C isotope ratio is to be studied in three planetary nebulae using the
 GHRS. The differing nuclear spins of the 12C and 13C nuclei create a total
 angular momentum coupling between the C++ 3P levels of 13C, giving rise to a
 radiative transition at the wavelength of the completely forbidden "J=0-0"
 transition in 12C. The large aperture of GHRS and an echelle grating are to be
 used to observe the two 12C III] lines at 1906.7 and 1908.7 and the 13C III] line
 at 1909.6A in the same echelle order. From the ratio of the 1909.6A line to the
 1908.7A line, and the electron density (computed from the ratio of the C III]
 1906.7 and 1908.7A lines), the 12C/13C ratio can be directly measured. We stress
 that measurement of the 1906.7/1908.7 flux ratio gives us the electron density in
 the C++ zone; this is needed for the interpretation of the 1909.6A line. The
 echelle provides enough dispersion that the separation of the lines will be
 sufficient to measure the weak 1909.6A line well away from the wings of the
 1908.7A line. From the expected range of 12C/13C ratios in possible PN
 progenitors stars, the 1909.6A line will be several hundred times fainter than
 the adjacent 1908.7A line. The expansion velocity of the PNs (~0.13A) is a factor
 seven less than the separation between the 13C and 12C lines (0.9A). In addition,
 GHRS tests show that a line observed with the GHRS+SSA has no `wings' above
 relative intensity 3.E-4 beyond a wavelength offset of 0.4A from line centre. Our
 13C line is offset by 0.9A from the 12C line. Finally, we note that light
 scattered from other orders onto the detector will not be a problem at this very
 high dispersion as there are no other   bright emission lines nearby in other
 orders. The targets have been chosen to give a high detection probability of the
 13C 1909.6A line by being bright in C III] emission and/or of Type I (PNs with
 high mass progenitor star; mostly O-rich), with predicted lower 12C/13C ratio.
 NGC3918 is so bright in C III] that we can easily reach a limiting ratio of
 12C:13C = 90:1.
------------------------------------------------------------------------------------
  4. Justification of need for HST observations.
  This proposal would not be scientifically feasible without the capabilites of
 the High Resolution Spectrograph aboard HST. The 13C emission line to be detected
 is weak, situated in the UV, and close to a brighter line (1908.7A). Together
 these requirements necessitate the light gathering power of HST, the UV
 capability and the high spectral resolution to separate the weak line from the
 nearby strong line. Even allowing for these advantages only a few nebulae with
 the highest suface brightness in the C III] line (and additionally not of very
 high density) can feasibly be observed in a reasonable time. Earlier we attempted
 to measure the ratio of the 1909.6A line to the main C III] lines, using the IUE
 and its small entrance aperture. However the extreme slowness of the IUE+SAP,
 together with the very small dynamic range of the IUE camera detector, enabled
 only a very poor result to be obtained: for NGC3918, 12C/13C > 3.  The GHRS's
 detector has a very much better dynamic range and the spectrograph gives the very
 high resolution we need. This project cannot be done with the IUE; it needs the
 GHRS.
                                                                  Page   3
------------------------------------------------------------------------------------
  7. Data reduction and analysis plans.
  It is proposed to adopt the standard pipeline calibration. We choose not to
 sample the inter-order background since there are no known emission lines nearby
 in the adjacent orders at 1846 or 1974A in PN. The electron density will be
 measured from the ratio of the C III] 1906.7 to 1908.7A lines using total line
 fluxes as well as line fits. We will attempt to fit the 1908.7A profile to that
 of 1909.6A (since they should be of the same shape) in order to determine the
 1909.6A line flux. In addition we have interactive Gaussian line fitting programs
 which can handle constraints on line wavelength as well as statistical errors. In
 the event of non-detection of the 13C line, we expect to be able to specify
 useful upper limits based on our extensive spectroscopic experience.
------------------------------------------------------------------------------------
  8. Additional comments or special requests.
  The coordinates given are from measurements on GASP frames. For NGC3918 we have
 eyeballed the centre of the nebula ( diameter ~ 15arcsec ) and for the two
 Magellanic Cloud nebulae have fitted a 2-D Gaussian. The coordinates agree very
 well with those determined from our own measurements of plates. All three objects
 - NGC3918, SMC-N2 and LMC-N122 - are bright in the UV ( mostly from the many
 emission lines ) and so spiral search will work well. For the Magellanic Cloud
 nebulae we have specified a LOCATE = YES since we need to centre the nebulae in
 the large aperture.
------------------------------------------------------------------------------------
 10. Resources to be supplied by investigator's institution(s).
  Sufficient computing resources are already available to all three investigators.
 Travel funds for final analysis and preparation of results for publication are
 also readily available.
------------------------------------------------------------------------------------
11. Address Information
Name:  ROBIN ES CLEGG                                      Category: PI
Institution: ROYAL GREENWICH OBSERVATORY
Address:  MADINGLEY ROAD
City: CAMBRIDGE CB3 0EZ                         State:
Zip Code:                                       Country: ENGLAND
Telephone: +44 223 374700
Telex (or e-mail): 817235
------------------------------------------------------------------------------------
TARGET LIST    a) Fixed Targets                                                                    ID = 3608c            [  4]
------------------------------------------------------------------------------------------------------------------------------------
 1 |     2      |           3           |              4             |  5     |   6    |  7  |              8
------------------------------------------------------------------------------------------------------------------------------------
Tar|   Target   |         Target        |            Target          |Coord   | Radial |Acqui|FLX|     Flux data
No |    Name    |       Description     |           Position         |Eqnx    |  Vel.  |Prblm|REF|
   |            |                       |                            |        |        |     |   |
------------------------------------------------------------------------------------------------------------------------------------
1   NGC3918      G,502                   PLATE-ID=06PS,               J2000    V = -20  EXT   1   F-LINE(1908) = 1.13 +/- 0.11 E-10
    PK294+4D1                            RA = 11H 50M 17.88S +/-                              2   SURF-LINE(1906) = 3.6 +/- 1.0 E-13
                                         1.5",                                                3   SURF-LINE(1910) = 4.7 +/- 1.5 E-15
                                         DEC = -57D 10' 56.6" +/-                             4   SURF(2000) = 1.4 +/- 0.2 E-11
                                         1.5"
     Comments: POSITION REFERS TO THE CENTROID OF THE
             NEBULA AS MEASURED ON GASP FRAME. FLUX 1
             IS SUM OF 1907+1909A LINES. NEBULA AREA ~
             180 SQ ARCSEC. FLUX 3 IS 13C 1910 LINE FOR
             12C/13C=90. FLUX 4 IS BROAD BAND 1100-
             3400A FOR TARGET ACQUISITI0N PASSBAND N2.
------------------------------------------------------------------------------------------------------------------------------------
2   SMC-N2 SMC-  H,502                   PLATE-ID=06B1,               J2000    V = 160        1   F-LINE(1907) = 1.49 +/- 0.15 E-12
    SMP2 SMC-MG2                         RA = 00H 32M 38.81S +/-                              2   F-LINE(1910) = 3.0 +/- 1.0 E-15
                                         1.5",                                                3   F(2000) = 6.2 +/- 1.5 E-12
                                         DEC = -71D 41' 58.9" +/-
                                         1.5"
     Comments: POSITION MEASURED ON GASP FRAME. FLUX 1
             IS SUM OF 1907+1908A LINES. FLUX 3 IS 13C
             1910 LINE FOR 12C/13C=30. FLUX 3 IS BROAD
             BAND 1100-3400A FOR TARGET ACQUISITI0N
             PASSBAND N2.
------------------------------------------------------------------------------------------------------------------------------------
3   LMC-N122 LM1 H,502                   PLATE-ID=05ZW,               J2000    V = 270        1   F-LINE(1907) = 1.13 +/- 0.11 E-12
    -28 LMC-WS18                         RA = 05H 19M 54.70S +/-                              2   F-LINE(1910) = 2.0 +/- 0.6 E-15
                                         1.5",                                                3   F(2000) = 6.1 +/- 1.5 E-12
                                         DEC = -69D 31' 05.1" +/-
                                         1.5"
     Comments: POSITION MEASURED ON GASP FRAME. FLUX 1
             IS SUM OF 1907+1908A LINES. FLUX 2 IS 13C
             1910 LINE FOR 12C/13C=30. FLUX 3 IS BROAD
             BAND 1100-3400A FOR TARGET ACQUISITI0N
             PASSBAND N2.
------------------------------------------------------------------------------------------------------------------------------------
EXPOSURE LOGSHEET                                                                                  ID = 3608c            [  5]
------------------------------------------------------------------------------------------------------------------------------------
 1      |   2   |      3    |  4   |   5   |   6   |    7   |   8   |       9       |10 |   11  |   12    |13 |14|        15
------------------------------------------------------------------------------------------------------------------------------------
  Line  |  Seq  |   Target  |Instr | Oper. | Aper  |Spectral|Central|   Optional    |Num|  Time |   S/N   |Flx|Pr|     Special
 Number | Name  |    Name   |Config| Mode  |or FOV |Element |Waveln.|  Parameters   |Exp|       |Rel. Time|Ref|  |   Requirements
------------------------------------------------------------------------------------------------------------------------------------
1.1              NGC3918     HRS    ACQ     2.0     MIRROR-N2        SEARCH-SIZE=5   1   75.0S             4   1  CYCLE 2
                                                                     BRIGHT=RETURN                                ONBOARD ACQ FOR
                                                                                                                  1.2
     Comments: EXTENDED OBJECT. ACQ ON
               BRIGHTEST POINT IN CENTRE OF
               NEBULA. ESTIMATED COUNT RATE IS
               1700 HZ.
------------------------------------------------------------------------------------------------------------------------------------
1.2              NGC3918     HRS    ACCUM   2.0     ECH-B    1908.3  STEP-PATT=1     2   37M     4         3   1  CYCLE 2
                                                                     FP-SPLIT=STD                73M
                                                                     DOPPLER=ON
     Comments: 13C 1910A LINE SEPERATED BY
               0.9A (43 CHANS) FROM 12C
               1908.7A LINE.
------------------------------------------------------------------------------------------------------------------------------------
2.1              SMC-N2      HRS    ACQ     2.0     MIRROR-N2        SEARCH-SIZE=3   1   90.0S             3   1  CYCLE 2
                                                                     BRIGHT=RETURN                                ONBOARD ACQ FOR
                                                                     LOCATE=YES                                   2.2
     Comments: SMALL EXTENDED NEBULA. DIAMETER
               ~ 0.7". ESTIMATED COUNT RATE IS
               160 HZ.
------------------------------------------------------------------------------------------------------------------------------------
2.2              SMC-N2      HRS    ACCUM   2.0     ECH-B    1909.3  STEP-PATT=1     2   43.5M   3         2   1  CYCLE 2
                                                                     FP-SPLIT=STD                81M
                                                                     DOPPLER=ON
     Comments: 13C 1910A LINE SEPERATED BY
               0.9A (43 CHANS) FROM 12C
               1908.7A LINE. REDSHIFT OF
               SMC~160KM/S
------------------------------------------------------------------------------------------------------------------------------------
3.1              LMC-N122    HRS    ACQ     2.0     MIRROR-N2        SEARCH-SIZE=3   1   90.0S             3   1  CYCLE 2
                                                                     BRIGHT=RETURN                                ONBOARD ACQ FOR
                                                                     LOCATE=YES                                   3.2
     Comments: SMALL EXTENDED NEBULA. DIAMETER
               ~ 0.7" ESTIMATED COUNT RATE IS
               180 HZ.
------------------------------------------------------------------------------------------------------------------------------------
3.2              LMC-N122    HRS    ACCUM   2.0     ECH-B    1910.0  STEP-PATT=1     4   49M     3         2   1  CYCLE 2
                                                                     FP-SPLIT=STD                178M
                                                                     DOPPLER=ON
     Comments: 13C 1910A LINE SEPERATED BY
               0.9A (43 CHANS) FROM 12C
               1908.7A LINE. REDSHIFT OF
               LMC~270KM/S
------------------------------------------------------------------------------------------------------------------------------------
            Summary Form for Proposal 3608c                                                                              [  6]

  Item                          Used in this proposal
------------------------------------------------------------------------------------------------------------------------------------
  Configurations                HRS
------------------------------------------------------------------------------------------------------------------------------------
  Opmodes                       ACQ ACCUM
------------------------------------------------------------------------------------------------------------------------------------
  Optional Parameters           SEARCH-SIZE=5 BRIGHT=RETURN STEP-PATT=1 FP-SPLIT=STD DOPPLER=ON SEARCH-SIZE=3 LOCATE=YES
------------------------------------------------------------------------------------------------------------------------------------
  Proposal for                  GO
------------------------------------------------------------------------------------------------------------------------------------
  S/C Hours                     5.53
------------------------------------------------------------------------------------------------------------------------------------
  Scientific Category           INTERSTELLAR MEDIUM
------------------------------------------------------------------------------------------------------------------------------------
  Scientific Sub-category       PLANETARY NEBULAE
------------------------------------------------------------------------------------------------------------------------------------
  Special Requirements          CYCLE 2; ONBOARD ACQ FOR 1.2 CYCLE 2 ONBOARD ACQ FOR 2.2 ONBOARD ACQ FOR 3.2
------------------------------------------------------------------------------------------------------------------------------------
  Spectral Elements             MIRROR-N2 ECH-B
------------------------------------------------------------------------------------------------------------------------------------
  Target Names                  NGC3918 PK294+4D1 SMC-N2 SMC-SMP2 SMC-MG2 LMC-N122 LM1-28 LMC-WS18
------------------------------------------------------------------------------------------------------------------------------------