Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/hst/stis/performance/sensitivity/software/ROBOT_STIS_MAMA.pdf Дата изменения: Wed Oct 31 21:15:24 2007 Дата индексирования: Sun Dec 23 20:53:44 2007 Кодировка: Поисковые слова: guide 8.0

The Integrated Bright Object Tool (BOT) ­ STIS/MAMAs
R. Downes, T. Rogers, K. Peterson December 21, 2006

Abstract A integrated Bright Object Tool (BOT) has replaced the old VTT-based RObust Bright Object Tool. The main engine for the tool, as well as the basic processing steps, has remained unchanged, but the source of the input data, as well as the display of the results, have been changed to provide a more complete tool. The tool will check each exposure in a program for field (and prime) objects that are either health-and-safety concerns, or may impact the scientific value of the data. The tool will utilize the GSC2 catalog to determine the brightness and (rough) spectral type of all objects in the macroaperture, determine the count rate and total counts for each object via a lookup table, and compare these values to limits set by the STIS Group. The output products will be a table listing the results for all objects, with the status of each object (health-and-safety concern, science concern, safe, or unknown status), and an Aladin image with the object's status indicated. The new tool utilizes information in the proposal file, and also uses the APT and Aladin interfaces for its tabular and graphical display, respectively. For Instrument Scientists, the use of the proposal file, instead of the ASSIST database, allows for the support of position changes (e.g. POS TARGs) for exposures. For GOs, the use of the proposal file allows for more than one exposure to be processed at one time, making it much easier to run the tool on the entire proposal.

Introduction
The VTT-based Robust Bright Object Tool (ROBOT) has be utilized by both GOs and Instrument Scientists since Cycle 10. One of the main deficiencies of the tool for Instrument Scientists has been the inability to handle exposures with positional changes (e.g. POS TARGs), which is due to the need to access the ASSIST database. For GOs, the need to run each exposure individually makes proposal checking extremely tedious. The new tool will utilize information in the proposal, which eliminates both problems. The tool will use information in the Phase II proposal to identify all the stars in the macroaperture that are in the GSC2 catalog. The color information of those stars will be converted to spectral types, and count rates (and total counts) for each star will be determined via a lookup table (based on Exposure Time Calculator results). The final products will be a tabular view of analysis of each star in the field (available through the APT interface) and a graphical view (available through the Aladin interface), in which all stars with health-and-safety concerns are labelled in red, all stars with science


concerns (e.g. bright targets that could bleed) are labelled in orange, all stars for which an analysis could not be performed (e.g. incomplete color information) are labelled in blue,and all stars that are safe are labelled in green. There will also be a printable and downloadable listing of the results for all targets. It is important to note that BOT will only be useful for field stars that are in the GSC2, and for the target if it is a normal star. Since most science targets are not normal mainsequence stars, use of the ETCs to fully verify the prime targets will still be required. Extended targets will not appear in the GSC2, and will therefore need to be checked by hand. Variable targets, although in the GSC2, will only have the magnitude at the time of the GSC2 plate, and may therefore not have the "correct" magnitude for the time of observation. While most variables have small amplitudes, some objects (e.g. cataclysmic variables and symbiotics) have large amplitudes, which could pose problems (either as field objects, or as the prime target). In this document, we describe how the tool works for the STIS/MAMAs. This tool will enhance (compared with the VTT-based ROBOT) the bright object checking performed by the Instrument Group, and can allow PIs to more easily do their own checks to assure their observations are valid from both a health-and-safety as well as scientific integrity perspective.

Assumptions
The following assumptions were made in implementing BOT processing: · The size of account for acquisition determined the macro-aperture (search radius) is padded over the nominal size to possible mispointings (but still close enough for the Guide Star to be considered successful) of HST. The size of the pad ­ 20.9" - was by the Instrument Group.

·

All field objects are Main Sequence stars. This is a reasonable assumption, although it will not be always correct (e.g. most prime targets are not normal stars). This is the only assumption possible due to only 1 color being available. All objects have no reddening. This is clearly incorrect in the plane, but is not unreasonable at high galactic latitude (where most HST observation are obtained). This is the only assumption possible due to only 1 color being available. Since reddening would decrease the ultraviolet flux, this is also the conservative assumption when doing health-and-safety checks.

·


·

For objects that have only an F magnitude, an extended search is performed around the position and assume the J magnitude of the object is equal to the faintest J magnitude detected. Since the object was not detected, and since we can detected objects at this limit, the object cannot be brighter than this limit. This conservative assumption allows us to process and clear many objects that would otherwise require "manual" processing. All objects with B-V<+0.1 are assumed to be O5V stars. This assumption is necessary due to the near degeneracy in the spectral type-color relation at the blue end. All objects above a Vcrit value (spectral element dependent) are assumed to be O5V stars. This assumption is necessary due to the lack of reddening information. The GSC2 flag indicating the object is not a star is ignored for all faint (V > 17) objects. This is due to the fact that the reason most of these objects have the flag set due to the poor S/N in the PSF. While is issue is important in determining the object can be used as a guide star, it is not relevant for bright object checking. Failure to do this resulted in a large number of "unknown" objects appearing in many fields, which then needed to be "manually" cleared.

·

·

·

Processing Steps
1. The user loads their Phase II APT file, and selects their desired exposure(s) to process. 2. The user clicks on the BOT button to bring up the tool, and clicks on the Update Display button to begin processing. 3. The GSC2 is searched for all objects (even those flagged as not usable as guide stars) within the macro-aperture. The macro-aperture is a circle centered on the fiducial point of the aperture (i.e. where the prime target will be placed) that encompasses the entire aperture with a pad to account for pointing errors. Detector Shape Radius 17.9" Radius in ROBOT 35.4" Radius in BOT 38.8"

STIS/MAMA quad

Note that this definition of the macro-aperture is not always consistent with the values in the SIAF files. All area targets are ignored. The information returned is the object name, coordinates, and magnitudes (F and J). If either the F or J magnitude is undefined, convert the default value of "-99.9" to "unknown". Note that Tycho entries in the GSC2 will have V and B-V, and these must be corrected to get them on the


standard system via: V(corrected) = V(Tycho) - 0.09*B-V(Tycho) B-V(corrected) = 0.85*B-V(Tycho) 4. The F and J magnitudes are converted to V and B-V via the following conversions: · for the northern hemisphere (determined by the coordinates of the stars) V = F + 0.03 + 0.44*(J-F) - 0.03*(J-F)2 + 0.02*(J-F)3 B-V = -0.04 + 0.69*(J-F) · for the southern hemisphere V = F + 0.03 + 0.43*(J-F) - 0.02*(J-F)2 + 0.02*(J-F)3 B-V = -0.03 + 0.73*(J-F) 5. Some objects in the GSC2 do not have both and F and J magnitudes, while other objects are not considered stars. The treatment of these objects depends on the detector selected, and is described below. Detector STIS/MAMA no F and no J F and no J list F, J, V, B-V, and rea For objects with F fainter than 17.0, do a son as "unknown", spec tral second query of the GSC2 using a 10 type as "no color info" arcminute radius centered on the target coordinates. From the targets detected in this query, select the J magnitude of the faintest object, and add (make brighter) 0.2 magnitudes. Use this value as the J magnitude of the target and process normally. For objects brighter than F=17.0, list J, V, B-V, and reason as "unknown", F as GSC2 value, spectral type as "no color info"

Detector STIS/MAMA

no F and J F and J, not a star list F, V, B-V, and reason Compute the V magnitude as though the as "unknown", J as GSC2 object were a star. If the V magnitude is value, spectral type as "no fainter than a cutoff value (which is the V color info" of an O5 star in the "worst" filter reddened by E(B-V)=0.6 which is just safe; if the object were reddened less, the object would be treated by the tool as an O5 star), then treat the object as a star. The cutoff values are FUV (25MAMA)= 15.8 and NUV (25MAMA)= 16.5


6. After the V and B-V is derived, a sanity check should be performed. If the V magnitude is fainter than 24 or brighter than -2.0, or if the B-V color is redder than 3.0 or bluer than -0.5, the photometry is faulty and should not be used. The V, B-V, and spectral type should be listed as "unknown". 7. The B-V color is converted to a spectral type (assumed main sequence) via the table below . The tool will adjust the color by the difference between the nominal error and the actual error (i.e. make the color bluer by [error - 0.28m]); for objects with inferred J magnitudes (see Step 5), do not correct for errors. To determine the error, use the square root of the sum of the squares of the F and J errors. Note that for the healthand-safety checks, we will treat all stars with B-V colors less than or equal to +0.1, and all stars brighter than or equal to a critical V (Vcrit) magnitude (filter/ grating dependent), as O5 stars; the Vcrit values are listed in Appendix 1 ­ Vcrit values. While this may result in false positives, analysis has shown that the rate is acceptably low. To interpolate, always take the bluest color (e.g. if the star has B-V=0.85, select K0). Color to Spectral Type conversion
B -V -0 . 3 2 -0 . 2 4 0.00 +0.14 +0.43 +0.63 +0.82 +1.41 +1.61 Spectral Type O5 B1 A0 A5 F5 G2 K0 M0 M4 B -V -0 . 3 0 -0 . 1 4 +0.03 +0.31 +0.59 +0.66 +1.15 +1.49 Spectral Type B0 B5 A1 F0 G0 G5 K4 M2

8. The exposure information is derived from the proposal file, and the relevant parameters are given below. Exposure Parameters Parameters spectral element, central wavelength, exposure time, aperture

Detector STIS/MAMA

9. Based on the magnitudes, apertures, and exposure information, determine the count rate and total counts for each star via a lookup table (see Appendix 2 - STIS Sample Lookup table). The table contains the count rate for all (see Appendix 3 ­ Number


of Instrument Configurations) instrument configurations for a V = Vo object. To scale for the true V magnitude of a star, multiply the table value by 10(0.4*[Vo-Vobj]). To determine the total counts, multiply the corrected count rate by the exposure time. For the STIS/MAMA imaging observations (spectral element not starting with G, E, or P), a slightly more complicated procedure is needed. The lookup table values have had the sky background contribution removed. After scaling the counts for the V magnitude, the sky contribution (see Appendix 4 - MAMA Imaging Sky Background Values) needs to be added back in. Also, a "field check" should be performed by summing the count rates for all the objects in the field and forming a "pseudo-object"; note that the count rates should be summed before adding in the (single) sky value. 10. Based on the count rates and total counts, perform the health-and-safety and science checks as described in the table below. For the "pseudo-objects", compare the count rate with the appropriate value in the table for the GLOBAL check only. Checks Performed by BOT
Detector STIS/FUV- MAMA Health-and-Safety (counts/second) Global: 200,000 (Imaging, E) Global 30,000 (1st order) Local 100 (imaging) Local 75 (spectroscopy) STIS/NUV- MAMA Global: 200,000 (Imaging, E) Global 30,000 (1st order) Local 100 (imaging) Local 75 (spectroscopy) 65536 Saturation (electrons) 65536


11. For all objects, produce a table giving the guide star name, coordinates, F and J magnitudes, converted V and B-V magnitudes, spectral type, signal (count rate and total counts), and an indication of the status of the object; a summary table should also be produced. For assumed spectral types (i.e. O5), make clear that the type is assumed and not derived from the B-V color. Note that this table is printable and downloaded to be a file.


12. For all objects, produce an overlay for Aladin which marks objects that are healthand-safety concerns in red, science concerns in orange, unknown concerns in blue, and safe objects in green.


Appendix 1 ­ Vcrit values
Given the degeneracy of B-V (and V-R) for the bluest stars, we want to be conservative and say that all stars with B-V less than some value should be considered O stars. Also, since we only have 1 color in the GSC, we have to worry about reddened O stars looking like later-type objects. To determine the appropriate color cutoff, I selected a cutoff (BV=+0.1), and determined what V magnitude (Vcrit) would make an O5 star (B-V=-0.3, so E(B-V)=0.4) safe. The checking rule would then be that all stars brighter than Vcrit and all stars with B-V<+0.1 are assumed to be O5, while the remaining objects have the spectral types set by their observed color. See the ROBOT document for more detailed analysis on the number of false positives. Instrument Detector Spectral Element STIS FUV F25ND5 F25ND3 F25LYA F25QTZ 25MAMA F25SRF2 G140L G140M E140M E140H NUV F25ND5 F25ND3 F25MGII F25CIII F25CN182 F25CN270 25MAMA F25QTZ F25SRF2 G230M G230L E230M E230H Central Wavelength Vcrit 4.5 9.5 12.6 15.0 17.0 16.5 1425 12.0 1420 9.0 1425 8.0 1416 7.5 4.8 9.8 13.2 12.8 15.0 15.0 17.3 17.3 17.4 2338 8.5 2376 12.0 1978 7.5 2263 6.6


Appendix 2 - STIS Sample Lookup table
The following items are used in creating the lookup table; · · · Exposure time = 1 V=10 (point source) for spectra, V=8 (point source) for imaging, E(B-V) = 0.0 Zodiacal light/Bright Earth = average
Spectral Type B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 B5 NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA FUV-MAMA FUV-MAMA FUV-MAMA FUV-MAMA FUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA FUV-MAMA FUV-MAMA FUV-MAMA FUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA NUV-MAMA Detector Spectral Element G230L G230M G230M G230M G140L G140M G140M G140M PRISM E230M E230M E230H E230H E230H E230H E230H E230H E140M E140H E140H E140H 25MAMA F25ND3 F25ND5 F25QTZ F25SRF2 F25MGII F25CN270 F25CIII Central Wavelength 2376 1687 2419 3055 1425 1173 1420 1714 1200 1978 2707 1763 2263 2513 2762 2013 3012 1425 1234 1416 1598 52X2 52X2 52X2 52X2 52X2 52X2 52X2 52X2 52X2
a

Aperture

Countrate Local/Global TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD

0.2X0.2 0.2X0.2 0.2X0.2 0.2X0.2 0.2X0.2 0.2X0.2 0.2X0.2 0.2X0.2 0.2X0.2 0.2X0.2 0.2X0.2 0.2X0.2


B5 B5 B5 B5 B5 B5 B5

NUV-MAMA FUV-MAMA FUV-MAMA FUV-MAMA FUV-MAMA FUV-MAMA FUV-MAMA

F25CN182 25MAMA F25ND3 F25ND5 F25QTZ F25SRF2 F25LYA

TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD TBD/TBD


Appendix 3 ­ Number of Instrument Configurations
To keep the lookup table manageable, we will make several simplifying assumptions. For ACS/SBC, no such assumptions were necessary. Based on the above assumptions, the following table estimates the number of entries in the lookup table for each instrument..

Instrument Configurations
Instrument Parameters Configur ations STIS FUV-MAMA spectra 8 cenwaves, 14 aperture FUV-MAMA imaging 6 filters NUV-MAMA spectra 7 cenwaves, 14 aperture NUV-MAMA imaging 9 filters 112 6 98 9 Spectral Types 13 13 13 13 1456 78 1274 117 Total


Appendix 4 - MAMA Imaging Sky Background Values
Detector Detector Filter NUV 25MAMA STIS F25SRF2 F25QTZ F25MGII F25CN270 F25CIII F25CN182 F25ND3 F25ND5 FUV 25MAMA F25SRF2 F25QTZ F25LYA F25ND3 F25ND5 Global Background Local Background 4774 2098 1634 1470 1472 1470 1547 1471 1468 19430 1915 7 7985 26 7