After detailed inspection of data of a full grating spectrum, a broad feature, seen in all scans, was noted close to the 157 micron line. This feature was also present however in the background observation. The feature consist of a broad - emission - 'bump' in the continuum peaking at about 159 microns and about 10 microns wide ( see figure). It should be noted that the feature is not readily visible in the AAR products.
As it was scientifically unlikely to be real, other L01 data from revolution 447, from the previous revolution 442 and the next revolution 448 were inspected. Note that revolution 447 was the first full revolution after the resumption of operations.
The result is :
TDT Target Presence of the feature -------- ---------------- ----------------------- 44200137 IRD+40540 No -------- ---------------- ----------------------- 44700327 IC 4406 No 44700574 M83 N01 No 44700672 W Hydra Yes 44700719 RHO OPH A#7 ? 44700720 RHO OPH A#8 ? 44700721 RHO OPH A#9 ? 44700722 RHO OPH A#10 Yes 44700723 RHO OPH A#11 Yes 44700724 RHO OPH A#12 Yes 44700725 RHO OPH A#13 Yes 44700726 RHO OPH A#14 Yes 44700727 RHO OPH A#15 Yes 44700928 RHO OPH E#1 Yes 44700929 RHO OPH E#2 Yes 44700930 RHO OPH E#3 Yes 44700931 RHO OPH E#4 Yes 44700932 RHO OPH E#5 Yes 44701013 HD143006 Yes 44701014 HD143006 Off Yes 44701411 IRC+20236 No -------- ---------------- ----------------------- 44800303 Alpha Boo No 44801304 Alpha Sco No 44801406 IRAS15408 No 44802202 IRAS23133 No 44802307 NGC7023 No 44804505 NGC6543 No -------- ---------------- -----------------------
The question mark for RHO OPH indicate that due to strong fringing the feature cannot be identified positively.
* Spacecraft pointing
-------------------
No correlations were found with:
. RA and DEC positions.
. the solar aspect angle.
* Instrument parameters
---------------------
No anomaly was found in:
. the temperature for all instruments.
. the illuminator commanded status.
. the illuminator current.
* Previous observation
--------------------
No correlation was found with the observation before the affected
one (they are different instruments/configurations).
It is believed that the anomalous feature detected in some of the observations from revolution 447 is a one-off problem. However, monitoring will continue.
Those observations where the feature has been clearly or tentatively detected (i.e. marked with 'YES' or '?' in the table above) have been recommended for rescheduling.
ISO Science Operations and LWS Instrument Team
04/08/97