README web version of /home/usg/OPS/MTS/readme_xml/readme_84088100

Principal Investigator Email Address

• pakull@astro.u-strasbg.fr

Estimated Total Execution Time (hours, including overheads)

• 19 hours

General Description

• The proposal aims to measure the radial velocity curve of the optically
   brightest (V=20.6) ultraluminous X-ray source (ULX P13) in the sky, both for stellar
   absorption lines of the A-type supergiant and for the HeII 4686 emission line thought
   to come from the accretion disk around the black hole (BH). The ULX is located in
   the southern spiral NGC7793. The observations will be used to derive the orbital
   period and pose strong constraints on the mass of the BH. This will help to decide
   whether or not ULXs harbour intermediate mass black holes.
  The galaxy (NGC~7793) harbours another bright X-ray source which is surrounded by
   the large (diameter =15 arcsec) radio/optical/X-ray nebula, S26, resembling W50
   around the galactic microquasar SS3433. S26 was the subject of two of our previous
   ESO proposals; in period 82 
  it received rating B, but no observations were carried out, and in period 84 we
   did not obtain time for this object.
  Since S26 is only 4.5 arcmin distant from P13 we decided to add scientific value
   to our observations by placing the slit in a way to include both objets. Note that
   we do not 
  want to impair the observations of our main target P13.

Waiver Requests

• No Waiver Request was submitted.
  We requested - and were granted by Dr Primas - InstrumentalSetupChange which concerned
   the use of grisms GRIS_1200R+93 and GRIS_1200B+97 which are better adjusted to our
   needs than the corresponding GRIS_600RI+19 and GRIS_600B+22 grisms.

Critical Observing Condition Constraints

• None

Time-Critical Aspects

• The program aims at monitoring (19 observations) the (abs+em) radial velocities
   of P13, for which we don't know the orbital period. Based on evolutionary and other
   arguments, we expect P_orb to be in the range of 10d - 60d. Therefore we request
   the observations to be more or less evenly distributed during the gray time over
   3 months from Oct 11 to Dec 31.
  An optimal distribution would be 6 observations each at gray time around new moons
   on October 18, Nov. 16, and Dec 16.
  Observations are planned mainly with the blue grism GRIS1200B+97 (16 observations)
   and only 3 with the red GRIS1200R+093. The red GRISM1200R+93 observations could
   well be accompanied by blue GRISM1200B+97 observations during the same night; however,
   two or more blue GRISM1200B+97 observations during the same night would not be useful.

Special Execution Requirements

• Acquisition of two targets P13 and S26 which are separated by 4.5 arcmin
   onto a long-slit has turned out to be rather difficult using the available FOR2
   templates. 
  However, the secondary target S26 is somewhat extended (10 arcsec for the brightest
   parts)
  that an error in the value of the pre-determined position angle might not be fatal.
  Based on recommendation by Dr. Bodo Ziegler, we have now settled on the solution
   to center
  P13 on the slit (rotator=-25.0 deg) and use a telescope offset of 235" in template
   FORS2_lss-obs_off_fast which is supposed to place P13 on the slit in the lower CCD
   
  and S26 onto the slit in the upper CCD. However, the question of how well
  P13 remains centered in the slit remains to be clarified.
  The latter issue is most important since centering not only determines the amount
   of light entering the slit, but also the wavelength calibration if the seeing is
   smaller than the 
  slitwidth. We tried to control the latter point by adding another "through-slit
   image" 
  using template  FORS2-lss-obs_slit_fast. However, we had to learn that the Template
   Manual states on p39: "At the end of the (science) exposure sequence the telescope
   moves to the start position". That would indeed impede our aim to check where in
   the slit the star was positioned during the science exposure.
  For a revised 2P2PP version we will also investigate another stategy recommended
   by Dr. Ziegler using the midpoint of the two targets.

Special Calibration Information

• ---(Empty)---

ToO Information

• ---(Empty)---

ToO Activators List

• ---(Empty)---

Is this a Pre-imaging run ?

• false

Pre-imaging Requirements

• ---(Empty)---

Source(s) of Pre-imaging

• ---(Empty)---

Pre-imaging sources not listed above

• ---(Empty)---

Do all your OBs comply with the instrument-specific requirements listed
 on the instrument-specific Phase 2 web page ?

• YES

If this is a pre-imaging run, did you select PRE-IMAGING for the Observing
 Category for each Observing Template ?

• N/A

Do all your finding charts comply with both the general and instrument-specific
 Phase 2 Web Pages ?

• YES

If you submitted OBs for standard stars, did you specify the magnitude
 and spectral type of all standard stars in the OBs ?

• N/A

Have you included OBs for any calibrations that you need but which are
 not part of the Calibration Plan ?

• N/A

If you are observing Moving Targets, have you attached suitable ephemeris
 files to your OBs?

• N/A

If you have preferences which OBs should be executed first, did you make
 use of the User Priority field in the OBs ?

• N/A

If this is a run that requires coordinated observations with other facilities,
 did you give proper instructions in the Time-Critical Aspects Section ?

• N/A

If you have prepared your finding charts with tools other than FIMS,
 do they comply with the specifications on the FORS1 Phase 2 web page ?

• YES