F OS FIL TERGRA TING WHEEL REPEA T ABILITY MEASUREMENTS - - PDF document

SLIDE 1 F OS FIL TERGRA TING WHEEL REPEA T ABILITY MEASUREMENTS ANURADHA K ORA TKAR and STEPHAN MAR TIN Sp ac e T elesc

• p

e Scienc e Institute

• San

Martin Drive Baltimor e MD

• Abstract

The p

• stCOST

AR F OS FilterGrating Wheel F GW rep eatabilit y w as tested for b

• th

the red and blue detectors The test consisted

• f
• btaining

rep eated F OS images in an unin terrupted sequence through

• dieren

t gratings

• n

eac h detector The

• bserv

ations consisted

• f

exp

• sures

using GH GH and GH with F OSRD and GH GH and GH with F OSBL All

• ther
• bserving

parameters w ere unc hanged during the test The standard deviations

• f

the p

• sitions
• f

sp ectra with resp ect to eac h

• ther

are found to b e indep enden t

• f

the c hosen grating The rms deviations

• f

the p

• sition
• f

the sp ectra in the F OS X and Y directions are

• f

the

• rder
• f
• dio

de and

• ybases

resp ectiv ely

• Deviations

as large as

• dio

des and

• ybases

are also seen These v alues are similar to those

• btained

from prelaunc h calibration activities The nonrep eatabilit y

• f

the F GW could b e a ma jor source

• f

instrumen tal inaccuracy in the w a v elength calibration

• f

sp ectra

• btained

without con temp

• raneous

calibration lamp sp ectra It should b e noted that the absolute w a v elength calibration for a t ypical F OS sp ectrum is not

• nly

aected b y in ternal instrumen tal eects suc h as F GW p

• sition

and ap erture lo cation but is also aected b y the target acquisition accuracy

• Key

w

• rds

F OS

• W

a v elength Calibration

• In

tro duction Preigh t measuremen ts

• f

the F OS ltergrating wheel F GW rep eatabilit y sho w ed that the F GW rep eatabilit y w as

• f

the

• rder
• f
• microns
• ybase

units in Y and

• dio

des in X in b

• th

the X and Y directions

• f

the F OS blue detector and

• f

the

• rder
• f
• microns
• ybase

units in Y and

• dio

des in X in b

• th

the X and Y directions

• f

the F OS red detector CALF OS CALF OS CALF OS This nonrep eatabilit y

• f

the F GW leads to w a v elength calibration errors Unin terrupted rep eated

• bserv

ations with dieren t gratings w ere

• btained

in the rst part

• f

the calibration program

• to

c hec k the F OS F GW rep eatabilit y

• The

red side detector measures used the GH GH and GH gratings while the blue side detector measures used the GH GH and GH gratings Observ ations for eac h grating are listed in T ables I IVI I Eac h

• bserv

ation w as in the F OS IMA GE mo de and sp ectra

• f

the in ternal PtCrNe w a v elength calibration lamp using the

• ap

erture w ere

• btained

in a con tin uous random sequence

• f

appro ximately

• exp
• sures

in eac h grating The F GW w as the

• nly

instrumen t comp

• nen

t that w as mo v ed during the en tire

• bserving

run for eac h detector whic h lasted

• min

utes for the red side detector and

• min

utes for the blue side detector The exp

• sure

times for eac h single exp

• sure

are giv en in T able I Other exp

• sure

details suc h as n um b er

• f

dio des used for eac h grating and the w a v elength range co v ered are also giv en in T able I

SLIDE 2 A K ORA TKAR AND S MAR TIN T ABLE I Exp

• sure

Characteristics for eac h Grating Cong Grating Exp

• sure

Dio de W a v elength Num b er

• f

Emission Time s Range Range

• A

Lines Used F OSRD GH

• F

OSRD GH

• F

OSRD GH

• F

OSBL GH

• F

OSBL GH

• F

OSBL GH

• Data

Analysis Since eac h IMA GE mo de

• bserv

ation used

• dio

des with NXSTEPS O VER SCAN YSTEPS and YSP A CE there w ere

• sp

ectra with

• pixels

eac h stored as

• groups

in the

• riginal

data le The

• sp

ectra w ere then con v erted in to t w

• dimensional

images with

• pixels

eac h using the STSD AS task r apid lo

• k

F

• r

eac h grating the rst image w as c hosen as the reference image The

• pixel

images w ere then crosscorrelated t w

• dimensionally

with the reference frame for eac h grating The STSD AS task cr

• ssc
• r

is used to determine the crosscorrelation see Bracew ell

• for

details Since the cen tering

• ption

is used in the cr

• ssc
• r

task the maxim um p

• w

er is exp ected at the

• pixel

p

• sition

in the cross correlated image for this analysis The shift

• f

an image with resp ect to the reference image is th us the p

• sition
• f

maxim um p

• w

er in the crosscorrelated image The cross correlated images are

• f

high signaltonoise since man y see T able I emission lines with signicance lev els

• ab
• v

e the bac kground are used in the crosscorrelation analysis The p

• sition
• f

maxim um p

• w

er in the crosscorrelated image is giv en in T ables I IVI I columns

• and
• The
• sets

with resp ect to the reference cen tral pixel columns

• and
• are

giv en also in the tables The measuring uncertain t y

• f

the cross correlation p eak is

• pixels

in X where

• pixels
• dio

de and

• pixels

in Y where

• ybases
• pixel

The standard deviations in units

• f

pixels for eac h grating are giv en in the tables

• Results

Only the deviations from the reference pixel are imp

• rtan

t for determining the F GW rep eatabilit y

• b

ecause the absolute v alue

• f

the reference pixel is arbitrary

• These

deviations are

• f

the same

• rder

for all gratings The

• rms

deviations

• f

the p

• sition
• f

the sp ectra are

• pixels

in the F OS Calibr ating HST Post Servicing Mission

SLIDE 3 F OS FIL TERGRA TING WHEEL REPEA T ABILITY X direction and

• pixels

in the F OS Y direction These rms deviations translate to

• dio

de in F OS X direction and

• ybases

in the F OS Y direction The range

• f

deviations is

• pixels

in F OS X

• dio

des and

• pixels

in F OS Y

• ybases

Since the deviations in the analysis are Gaussian distributed w e can exp ect

• deviations

as large as

• pixels
• dio

des in F OS X and

• pixels
• ybases

in F OS Y sometimes W e see that the range

• f

deviations for the red detector are sligh tly larger than for the blue detector W e ha v e noted in a previous instrumen t rep

• rt

CALF OS that the lo cation

• f

the F OS sp ectra are aected b y the am bien t magnetic eld in the detector The duration

• f

the en tire

• bserving

run for eac h detector in this calibration program is long enough that magnetic eld eects could b e signican t Th us the scatter in the lo cation

• f

the sp ectra

• bserv

ed in the presen t analysis could b e not

• nly

due to the F GW but also due to c hanges in the magnetic eld en vironmen t W e note that the amoun t

• f

deviation in the p

• sition
• f

the sp ectra

• btained

in this test are similar to those

• btained

during prelaunc h calibration measuremen ts CALF OS

• CALF

OS CALF OS Th us the p

• stCOST

AR test indicates that there has not b een dramatic w ear in the F GW notc hes that hold the grating in a giv en lo cation F urther since the prelaunc h measuremen ts w ere in a constan t magnetic eld and sho w ed similar deviations as the p

• stCOST

AR measuremen ts w e conclude that the scatter in the lo cation

• f

the F OS sp ectra due to nonrep eatabilit y

• f

the F GW is no less than the scatter induced b y the magnetic eld en vironmen t The scatter along the F OS Y direction p erp endicular to the disp ersion axis aects the ux calibration at a lev el

• and
• nly

for the large ap ertures

• and
• since

the sp ectrum can b e misdirected

• n

to the dio de arra y

• The

scatter in the F OS X direction along the disp ersion axis leads to w a v elength uncertain ties in the range

• f
• dio

des F

• r

a t ypical F OS

• bserv

ation uncer tain ties in the absolute w a v elength calibration are due to a the nonrep eatabilit y

• f

the F GW b the uncertain t y in the lo cation

• f

the F OS ap ertures in the F OS X direction whic h ranges from

• to
• dio

des CALF OS

• c

the c hanges in the am bien t magnetic eld

• f

the detector and d the target acquisition accuracy

• Of

these four sources

• f

uncertain t y

• the

nonrep eatabilit y

• f

the F GW is the dominan t in ternal instrumen tal source

• f

inaccuracy in the w a v elength calibration

• f

sp ectra A con temp

• raneous

calibration lamp sp ectrum without an y c hange in the ap erture p

• sition

can reduce the eect

• f

F GW

• n

w a v elength calibration Calibr ating HST Post Servicing Mission

SLIDE 4 A K ORA TKAR AND S MAR TIN T ABLE I I F OSRD GH Grating Observ ations Ro

• t

name X p

• sition

Y p

• sition

X Oset Y Oset pixel pixel pixel pixel ynct

• ynct
• ynct
• yncct
• yncft
• ynckt
• yncm

t

• yncpt
• ynctt
• standard

deviation

• range
• T

ABLE I I I F OSRD GH Grating Observ ations Ro

• t

name X p

• sition

Y p

• sition

X Oset Y Oset pixel pixel pixel pixel ynct

• ynct
• yncbt
• yncet
• ynch

t

• yncjt
• ynclt
• yncot
• yncqt
• yncst
• standard

deviation

• range
• Calibr

ating HST Post Servicing Mission

SLIDE 5 F OS FIL TERGRA TING WHEEL REPEA T ABILITY T ABLE IV F OSRD GH Grating Observ ations Ro

• t

name X p

• sition

Y p

• sition

X Oset Y Oset pixel pixel pixel pixel ynct

• ynct
• ynct
• ynct
• yncat
• yncdt
• yncgt
• yncit
• yncn

t

• yncrt
• yncut
• standard

deviation

• range
• T

ABLE V F OSBL GH Grating Observ ations Ro

• t

name X p

• sition

Y p

• sition

X Oset Y Oset pixel pixel pixel pixel ynczt

• ynczt
• ynczt
• ynczct
• ynczft
• ynczkt
• ynczm

t

• ynczpt
• yncztt
• standard

deviation

• range
• Calibr

ating HST Post Servicing Mission

SLIDE 6 A K ORA TKAR AND S MAR TIN T ABLE VI F OSBL GH Grating Observ ations Ro

• t

name X p

• sition

Y p

• sition

X Oset Y Oset pixel pixel pixel pixel ynczt

• ynczt
• ynczbt
• ynczet
• ynczh

t

• ynczjt
• ynczlt
• ynczot
• ynczqt
• ynczst
• standard

deviation

• range
• T

ABLE VI I F OSBL GH Grating Observ ations Ro

• t

name X p

• sition

Y p

• sition

X Oset Y Oset pixel pixel pixel pixel ynczt

• ynczt
• ynczt
• ynczt
• ynczat
• ynczdt
• ynczgt
• ynczit
• ynczn

t

• ynczrt
• ynczut
• standard

deviation

• range
• Calibr

ating HST Post Servicing Mission

SLIDE 7 F OS FIL TERGRA TING WHEEL REPEA T ABILITY References Bracew ell R N

• The

F

• urier

T r ansform and Its Applic ation nd e d New Y

• rk

Dahlem M

• Koratk

ar A

• P
• stCOST

AR F OS Ap erture Wheel Rep eatablilt y Measure men ts CALF OS

• Hartig

G

• F

OS FilterGrating Wheel Rep eatabilit y CALF OS

• Hartig

G

• Impro

v emen ts in the FilterGrating Wheel Rep eatabilit y CALF OS

• Hartig

G

• F

OS FilterGrating Wheel Rep eatabilit y CALF OS

• Koratk

ar A Key es C

• Holfeltz

S

• Lo

cation

• f

F OS Sp ectra Cycle

• CALF

OS

• Calibr

ating HST Post Servicing Mission