8722( 7) - 08/23/02 09:26 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8722 Version: 7 Check-in Date: 10-Jul-2000 12:13:07 1.Proposal Title: Is Cir X-1 associated with SNR G321.9- 0.3? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle SNAP 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Roberto Mignani European Southern Observatory - Germany CoI: Dr. Patrizia Caraveo Istituto di Fisica Cosmica/CNR N CoI: Dr. Paolo Goldoni Service d'Astrophysique de CEA N ------------------------------------------------------------------------------------ 5. Abstract Cir X-1 is one of the most intriguing galactic X-ray sources. It is a ~ 16.6 d variable X/radio source, a type I X-ray burster and a QPO emitter, which, in spite of an ambiguous optical counterpart classification, identify it as an LMXB. The source is embedded in a radio nebula, with finer structures protruding towards the centre of the nearby SNR G321.9-0.3. This prompted the speculation about a connection between the two, with Cir X-1 being a runaway binary originated from the supernova explosion. In this case, a a significant proper motion would be expected for Cir X-1. Since this source has been already imaged by HST in 1992, one more WFPC2 image could allow to measure its proper motion in the expected direction. This, together with securing the association with the SNR, will constrain the age of the neutron star in Cir X-1, crucial to trace its magnetic field evolution in an accretion regime and to provide observational inputs to theoretical models. , bf This is a case where a single, very simple, and short observation can greatly contribute to solve an important astrophysical issue. ------------------------------------------------------------------------------------ 8722( 7) - 08/23/02 09:26 - [ 2] Observations Description ------------------------ We propose to perform a short WFPC2 observation of Cir X-1 through the 785LP ``I-filter'', where the source is brighter (m_785LP ~eq 18). In order to achieve the highest positional accuracy, our target should be centered in the PC chip (45 mas/pixel) of the WFPC2. After nailing its position with a few mas precision, it will be compared with the reference one obtained from the 1992 WFPC image of Mignani et al., taken through the same filter and still the best available image of the field. Although the 1992 image was obtained with the aberrated optics of the pre- refurbished HST and in the WFC configuration (i.e. with a coarser 100 mas pixel size), our target (star C) was still positioned with an accuracy of ~eq 10 mas or better. As it is seen from Fig.1, the PC f.o.v. (35 * 35 arcsec) is large enough to include a sufficient number of reference stars required to register the two frames. As in the first image, an exposure time of 5 min will be sufficient to detect the star with an high S/N. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8722( 7) - 08/23/02 09:26 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR-1520- STAR, LMXB RA=15H 20M 40.84S +/- 0.1S, J2000 V = 21 5709 DEC=-57D 9' 59.0" +/- 1", PLATE- B-V = 0. ID=00H6 Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1995.7 0.0 0.0 0.0 8722( 7) - 08/23/02 09:26 - [ 4] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR-1520-5 WFPC2 IMAGE PC1-FIX F785LP 7800 1 300 S 709 ------------------------------------------------------------------------------------------------------------------------------------ 2 STAR-1520-5 WFPC2 IMAGE PC1-FIX F785LP 7800 1 300 S 709 ------------------------------------------------------------------------------------------------------------------------------------ 3 STAR-1520-5 WFPC2 IMAGE PC1-FIX F785LP 7800 1 300 S 709 ------------------------------------------------------------------------------------------------------------------------------------ 8722( 7) - 08/23/02 09:26 - [ 5] Summary Form for Proposal 8722 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category SNAP ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F785LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names STAR-1520-5709 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 7800 ------------------------------------------------------------------------------------------------------------------------------------