Principal Investigator Email Address
schnurr@astro.umontreal.ca
Estimated Total Execution Time (hours, including overheads)
4.1h
General Description
In this project, we will carry out repeated, AO-assisted, intermediate-S/N, K-band spectroscopy of the six central star in R136, namely the stars BAT99-106 and BAT99-108 through BAT99-112 (henceforth, we will omit the BAT99 prefix) . One star is known to be a binary with a period of 4.377 days. However, it is not known which of these six stars is the binary, hence the primary goal of this present run is to identify the culprit, using seven spectra per star distributed wisely over the binary phase. In Time-Critical Aspects, we propose (but do not impose) a pattern with which the binary phase can be sampled ~equidistantly. Since it is possible that the binary is in an extremely crowded field, the secondary objective of this run will be to test in how far spatial dithering can yield a better data for PSF fitting to de-blend the crowded stars (see next paragraph). This test will be performed only in one OB. The Database ID of this test OB is 205138 while for the remaining six OBs, not such dithering is carried out. As you can see from the 8" x 8" finding chart made from a HST/STIS frame (e.g. Phase I proposal), the six stars can be observed in four pointings, given SINFONI's FOV of 0.8" x 0.8" in high-resolution mode. However, stars 108, 109, and 110 are heavily crowded, even STIS has difficulties to resolve them. In order to evaluate the potential of spatial dithering for future SINFONI observations (i.e. the follow-up once the binary has been identified), we will offset the IFU along the long side of the spaxels (i.e., along the Y or north-south axis) by 12.5 mas (half a spaxel) in order to increase the on-chip resolution to 12.5 x 12.5 sqmas (instead of the final 25 x 25 sqmas resolution that comes out of the reduction pipeline). To our best knowledge, this approach is as of yet untested. Hence, in order to validate the result, we will perform this dithering for two of our pointing, but only in one of our seven OBs (it's just a test, after all), namely the one with the Database ID 205138. Note here an important difference with our Phase I proposal: We forgot to include a dithered "reference star" (i.e. to see what a single PSF looks like after dithering). Therefore, we will additionally dither on star 111 (first pointing, AO-NGS and "our private PSF reference", newly added in Phase II) and on the pointing which includes stars 108, 109, and 110 (as proposed in Phase I). Furthermore, in this test OB, we will increase the total exposure time to 400s (4 NDIT x 100s DIT) per pointing in order to obtain a total S/N~140. This is the lower limit of S/N that will be required for our follow-up observations, so we consider this to be a viable test case for dithering with almost "real-life data". The observation sequence in this OB 205138 is thus the following: acquisition of star 111 and locking the AO loop (AO-NGS); first and second pointing (one dithering, cf. the following paragraph); offset to star 112, third pointing; offset to star 106, fourth pointing; offset to stars 108, 109, and 110, fifth and sixth pointing (one dithering). Since we have derived relative positions from STIS frames, offset errors should be close to non-existent and all target stars should fall well inside SINFONI's FOV, even if the P2PP verification tool warns that the specified targets will lie outside the FOV. For the remaining six OBs, no dithering is performed, and the exposure times per DIT are shorter: only four pointings with 2 (NDITS) x 150s (DIT) each, so to be compliant with SINFONI's exposure time policy. According to the P2PP estimation of the total execution time, we use 4h01m58s, i.e. 4m02s less than granted. During no exposure we come close to saturation. Note that due to the brightness of the target stars, no sky frames at all will be taken. See also Special Execution Requirements.
Waiver Requests
No Waiver Request was submitted
Critical Observing Condition Constraints
As specified in each individaul OB description, the seeing has to be 0.6" or better, and the target has to be observed at aimrasses of 1.5 or better. This is absolutely necessary to achieve the required spatial resolution, given how crowded the field is (in particular stars 108, 109, and 110). Given the outstanding weather conditions at Paranal in December/January, these conditions should be easily met during a wide observation window of plus/minus ~3 hours around meridian passage of the targets We leave the possibility of twilight observations to the discretion of the scheduler, as long as the AO loop works properly and the background in K does not increase. See Time-Critical Aspects for further information.
Time-Critical Aspects
The goal of this present run is to identify a 4.377d binary among the six observed stars. We did not specify time contraints in our Phase I, and we won't do so here. However, in order to optimize phase coverage and to increase the probability to identify another, possibly longer-period binary star among the six central stars, we propose that the stars be observed not more often than every second night. Hence, best-case scenario is that the 7 observation blocks will be spread out over roughly a fortnight. Given the airmass constraints (better than or equal to 1.5) and the target location in the sky, the objects can be observed easily within the ~6 hours (plus/minus ~3 hours) around meridian passage, essentially during most of the short nights during southern summer. This leaves a large flexibility to the scheduler. We expect that the required meteorological conditions (in particular the seeing of 0.6" and better, to maximize the achieved Strehl ratio) are met very frequently during southern summer on Paranal. However, should one night be too bad for an OB to execute, the OB in question should be retried the following (the next possible) night; then, the two-night interval should be resumed. We are convinced that the sampling is still robust enough to easily identify the binary star by its radial-velocity (RV) variations. IMPORTANT NOTE: Please do under all circumstances avoid to execute more than one OB per night. Thank you very much.
Special Execution Requirements
Our observations are pretty straight forward. Once the AO loop has successfully been closed, all should run by itself. Indeed, successful closing of the AO loop will be the only challenge, because the AO-NGS is somewhat crowded and not outstandingly bright, as can be seen from the 60" x 60" finding chart. This chart has been taken from the ground with the CTIO-0.9m imager in the Stromgren b band and under very good seeing conditions, and thus should match the image quality of Paranal in the infrared. For comparison and orientation purposes, we have included a 30" x 30" finding chart taken with HST/STIS in the blue-visible band (longpass below 5500 Angstrom). It matches SINFONI's AO-assisted resolution (i.e. after closing the loop), and since all bright stars in the field are of ~same spectral type, they should look similar in the K band. The exposure time for the acquisition frame is DIT=10s, yielding a S/N~10 for the AO-NGS (BAT99-111, the faintest of our six target stars). We were told that this should be fine. Please note that the high-resolution finding charts with the 8" x 8" FOV have been constructed from the same HST/STIS frame. They should accurately reflect what you see on your acquisition screen after the AO is locked. Exposure times are way on the safe side, since for our brightest target star (108) and under 0.6" seeing (z=1.5), one 300s exposure yields only ~4800 counts. Even under exceptionally good conditions at zenith (and a slightly brighter magnitude), we will not saturate the detector, despite the fact that WR stars are emission-line objects. Please note that no sky frames at all are required, as well as no telluric or other standard star. Thus, all offsets produce "Object" frames. Filenames for the finding charts are (in order of observation): 60by60_CTIO-b.jpg 60"x60" CTIO-0.9m Stromgren b 30by30_HST-STIS.jpg 30"x30" HST/STIS longpass 8by8_BAT111_HST-STIS.jpg 8"x 8" HST/STIS star 111 (AO-NGS) 8by8_BAT112_HST-STIS.jpg 8"x 8" HST/STIS star 102 8by8_BAT106_HST-STIS.jpg 8"x 8" HST/STIS star 106 8by8_BAT108-109-110_HST-STIS.jpg 8"x 8" HST/STIS stars 108-110 Good luck and thank you very much!
Special Calibration Information
None required.
ToO Information
None.
ToO Activators List
None.
Is this a Pre-imaging run ?
false
Pre-imaging Requirements
None required.
Source(s) of Pre-imaging
Pre-imaging sources not listed above
HST/STIS
Do all your OBs comply with the instrument-specific requirements listed on the instrument-specific Phase 2 web page ?
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 ?
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
Did you indicate the magnitude of the brightest object in the field in each SINFONI OB?
If you are using the AO: Did you indicate for every OB the magnitude of the guide star, and its distance to the target (if any)?
If you submitted OBs for standard stars, did you use the provided StandardStar templates?
N/A
If you are using a specific offset pattern or position angle: did you check carefully the definition in the manual?
Did you make really sure that none of your OBs ever saturates the detector?
If you are using the AO: did you enter the correct Strehl Ratio (on-axis, K-band) AND the seeing value in the constraint set?