Transcript Power Point - Astronomer`s Proposal Tools Team

The Bright Object Tool
Ron Downes
August 2007
Outline
•
•
•
•
Documentation
High-level assumptions
Limitations
How it works (the guts)
– Basic processing
– Low-level assumptions
• Use of other catalogs (GALEX, 2MASS)
• Sample output
– Table view
– Graphical (Aladin) view
• Search Sizes and Triggers (background info)
Documentation
• can be found at:
http://apst.stsci.edu/apt/apt-bright-objects/index.html
• Includes:
 New Bright Object Tool Documentation (Detectorspecific)
 New Bright Object Tool Testing (Detector-specific)
 Original Bright Object Tool Documentation (general)
• Movie can be found at:
http://apst.stsci.edu/apt/external/help/movies/SBC.html
High-level Assumptions
•
the search area 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, padded to account for possible mispointings (padding values
come from the instrument teams).
•
all objects are Main Sequence stars (with only 1 GSC2 color, this is the best
we can do).
•
all objects are unreddened (with only 1 GSC2 color, this is the best we can
do). This is clearly incorrect in the plane, but is not unreasonable at high
galactic latitude (where many HST observation are obtained). Since
reddening would decrease the ultraviolet flux, this is also the conservative
assumption when doing health-and-safety checks.
•
low-level assumptions (detector specific) are noted in the detailed
explanation of how to tool works.
Limitations
• assumes all field stars are normal MS stars (use the ETC for prime
target)
• no extended targets are checked (not in GSC2)
• variable targets only use magnitude at time of GSC2
• STIS/MAMA: M and H gratings only have the bluest and reddest
central wavelength in the tool - when processing an intermediate
settings, the tool selects the closest value
• ACS/WFC and ACS/HRC: only 2 gains per detector are supported,
and polarization is not supported
• NICMOS: polarization is not supported
• COS: only selected central wavelengths are in the tool
• WFC3/IR: grisms are not supported
• WFC3/UVIS: grisms and quad filters are not supported
How it works - Overview
• obtain exposure information from the Phase II
proposal
• based on target coordinates and aperture,
search GSC2 for all stars in the search area
• convert GSC2 F and J to V and B-V
• use B-V to determine spectral type
• determine counts and count rates for each star
based on ETC-generated lookup tables
• compare with trigger limits
• display results in both tabular and graphical
output
How it works - Details
1) load APT file and select exposures/visits to process
2) select BOT tool and click on Update Display button to
process
3) GSC2 is searched for all objects in the search area.
The information returned is the name, coordinates, and
magnitudes (F and/or J for faint objects, V and B-V from
Tycho for bright [V<12] objects). For COS, BOT checks
for objects in both apertures.
Details – cont.
Magnitude Cases
a) Objects with F and J – processing continues
b) Objects with no F and no J - processing stops
c) Objects with J and no F - processing stops (except
WFC3/IR)
For WFC3/IR objects with only a J mag, an extended
search is performed around the position and the F mag
of the object is assumed to be equal to the faintest F
mag detected. This conservative assumption allows us
to process and clear many objects that would otherwise
require "manual" processing.
Details – cont.
d) for objects with F and no J - processing stops (except for
ACS/SBC, STIS/MAMA, WFC3/IR, and COS)
For ACS/SBC, STIS/MAMA, and COS objects that have
only an F mag, an extended search is performed around
the position and the J mag of the object is assumed to
be equal to the faintest J mag detected. This
conservative assumption allows us to process and clear
many objects that would otherwise require "manual"
processing.
For WFC3/IR objects that have only an F mag, assume
the object is an M2V star (with appropriate J-F), and
continue processing.
Details – cont.
e) for objects with F and J, but "not a star" - processing stops (except
for ACS/SBC, STIS/MAMA, WFC3, and COS)
For ACS/SBC, STIS/MAMA, WFC3, and COS, the GSC2 flag
indicating the object is not a star is ignored for all faint (detectorspecific cutoffs) 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 this issue is important in determining if the object can be used
as a guide star, it is not relevant for bright object checking. Failure
to do this results in a large number of "unknown" objects appearing
in many fields, which then need to be "manually" cleared.
Note that an additional step has been proposed to handle cases with
only 1 magnitude (will discuss later).
Details – cont.
4) F and J are converted to V and B-V via standard conversions (with
some sanity checks)
5) B-V is used to determine a spectral type (with adjustments due to
unusually large photometric errors)
For ACS/SBC, STIS/MAMA, and COS, 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.
For ACS/SBC, STIS/MAMA, and COS, all objects brighter than a
Vcrit value (spectral element dependent) are assumed to be O5V
stars. This assumption is necessary due to the lack of reddening
information.
Details – cont.
6) adjust the V magnitude for ACS/SBC and COS
observations to account for the deviations of real stars
from the models (as is done in the ETC)
7) based on magnitude, spectral type, and exposure
information, determine the count rate and total counts
for each star in the search area via ETC-based lookup
tables
For COS and STIS spectroscopy, the aperture
throughput is taken into account.
Details – cont.
8) for ACS/SBC, STIS/MAMA, and COS, also
perform a global field check
9) compare the count rates and total counts
against trigger values to determine the status of
each object (trigger values for each detector
included in handout)
10) present the results both a tabular and
graphical format
Change to single mag processing
• For ACS/SBC, STIS/MAMA, and COS
• When only 1 magnitude is available,
assume the object is O5V
• Determine if object is safe
• If safe, mark object as such
• If not safe, continue with extended field
search
• ACS/STIS has signed off, need COS
Use of other catalogs
• 2MASS for WFC3/IR
– Search 2MASS catalog for field objects
(ignore contaminated objects)
– No spectral type determination needed
– Use J or H magnitude, depending on filter, to
determine count rates
– Fall back to GSC2 if no 2MASS data
Use of other catalogs – cont.
• GALEX problems
– Incompleteness
• Crowded fields (LMC, Galactic Plane)
• UV bright objects (most O and B stars)
– How to use fluxes to determine count rates
– Spectral typing not useful (most objects are A stars)
– Cross-matching between GSC2 and GALEX
problematic
– Decision: GALEX not used (should revisit once
GALEX survey is more complete)
How to Run BOT
• There is a training video that shows how to
run the tool and explains the output:
http://apst.stsci.edu/apt/external/help/movies/SBC.html
• You run the tool just like any other APT
tool (select the exposure(s) in the Tree
Editor and select BOT)
Sample Outputs - Tabular
Prior to Processing
Post-processing
Details Page
Sample Outputs - Graphical
Post-processing
GSC2 in background
POS TARG
Parallel
Search Sizes
Detector
Radius
Detector
Radius
ACS/SBC
35.0”
NICMOS/NIC1
19.7”
ACS/WFC
169.7”
NICMOS/NIC2
26.4”
ACS/HRC
26.5”
NICMOS/NIC3
49.2”
COS
8.3”
STIS/CCD
50.0”
STIS/MAMA
38.8”
WFC3/IR
105.0”
WFC3/UVIS
124.2”
Trigger Values
Detector Class
ACS/SBC H&S
H&S
Science
Type
Global
Local
None
Value
200,000 ct/s
50 ct/s
ACS/HRC H&S
None
Science Saturation 131,000 e(gain=2)
Science Saturation 155,000 e(gain=4)
Trigger Values – cont.
Detector
Class
Type
ACS/WFC
H&S
None
Value
Science Saturation 65,535 e(gain=1)
Saturation 85,000 e(gain=2)
Trigger Values – cont.
Detector
Class
Type
NICMOS/NIC1 H&S
None
Science Saturation
Value
145,000 e-
NICMOS/NIC2 H&S
None
Science Saturation
145,000 e-
NICMOS/NIC3 H&S
None
Science Saturation
185,000 e-
Trigger Values – cont.
Detector
Class
Type
Value
COS/NUV
H&S
Global
90,000 ct/s
H&S
Local
675 ct/s
Science
Saturation
TBD
H&S
Global
15,000 ct/s
H&S
Local
40 ct/s
Science
Saturation
TBD
COS/FUV
Trigger Values – cont.
Detector
Class
Type
STIS/CCD
H&S
None
Science
Saturation
Science
Saturation
Science
Residual
Image
Value
30,000 e(gain=1)
120,000 e(gain=2)
500,000 e-
Trigger Values – cont.
Detector
Class
Type
Value
STIS/MAMA H&S
Global
H&S
Global
H&S
Local
H&S
Local
200,000 ct/s
(imaging, E)
30,000 ct/s
(1st order)
100 ct/s
(imaging)
75 ct/s (spec)
Science Saturation
65536 e-
Trigger Values – cont.
Detector
Class
WFC3/IR H&S
Science
Science
Science
Type
Value
None
Min. (<10x)
Saturation
Mod. (<100x)
Saturation
75,000 750,000 e-
Ext. (>100x)
Saturation
>7,500,000 e-
750,001 7,500,000 e-
Trigger Values – cont.
Detector
Class
WFC3/UVIS H&S
Type
Value
None
Science Min. (<10x)
Saturation
80,000 800,000 e-
Science Mod. (<100x) 800,001 8,000,000
e
Saturation
Science Ext. (>100x)
Saturation
>8,000,000
e-