F OS INSTR UMENT AND CALIBRA TION ST A TUS� ���� � ���� ANURADHA K ORA TKAR Sp ac e T elesc op e Scienc e Institute� ���� San Martin Drive� Baltimor e MD ����� Abstract� The F ain t Ob ject Sp ectrograph �F OS� is op erating w ell and all its instrumen tal mo des are functional� There has b een an enhancemen t for the pip eline calibration that accoun ts for scattered ligh t correction� temp oral c hanges in the instrumen t sensitivit y and fo cus c hanges� These calibration c hanges can b e applied to pre�COST AR data p ost�facto� The calibration c hanges to the CALF OS soft w are will b e a v ailable for p ost�COST AR data in Septem b er ����� and will b e incorp orated in to the HST calibration pip eline� In addition to c hanges to the calibration pro cedure� new mo des of op eration that ha v e b een added to enhance target acquisition capabilities� The �F OS assisted GHRS target acquisition� tec hnique has b een dev elop ed primarily to allo w guest observ ers �GOs� acquire fain t targets and obtain GHRS sp ectroscop y � The �reuse�target�o�set acquisition� capabilit y w as dev elop ed to so that a program could ha v e more e�cien t target acquisitions if there w as more than one visit to the same target� F OS � Status � Calibration Key w ords� �� F OS Calibration Status ��� Dead Diodes Occasionally � one of the ��� dio des on either of the F OS detectors b ecomes noisy or ceases to collect data� When suc h a dio de is disco v ered� the dio de is monitored to determine its b eha vior� If the dio de is dead or the noisy b eha vior p ersists� the dio de is disabled and dio de n um b er is added to a list of dead dio des� with a particular e�ectiv e date� Presen tly � sev eral dio des are �under scrutin y �� but no new additions ha v e b een made to the dead dio de tables �DDT� since Decem b er ����� Curren tly � �� F OS�BL and �� F OS�RD dio des are disabled� The latest DDTs are giv en in a pap er b y Christensen and Martin� in these pro ceedings� Since the DDTs are only up dated p erio dically � it is p ossible that some data can b e pro cessed through the CALF OS calibration pip eline without correction for newly disco v ered dead dio des� An uncorrected dead dio de pro duces a c haracteristic signature in the data� whic h can b e corrected� F or details consult the F OS section of the HST Data Handb o ok� The latest v ersion of the DDTs are a v ailable via the F OS home page on the w orld wide w eb �WWW�� These should b e consulted to insure that data ha v e b een pro cessed with the most appropriate dead dio de reference �le� Summary Dead or noisy dio des ma y not b e corrected for in some F OS datasets� All observ ers and arc hiv e users should consult the latest v ersion of the DDTs to ensure that data ha v e b een pro cessed with the most appropriate dead dio de reference �le� ��� Ba ck gr ound Subtra ction The F OS sp ectral bac kground is particle�induced� A bac kground correction for all F OS gratings is no w included in the CALF OS calibration pip eline� Note that F OS
A� K ORA TKAR sp ectra su�er also from grating scatter and require a scattered ligh t correction� Please see the subsection b elo w on scattered ligh t for details� In the last calibration w orkshop� Rosa ������ had rep orted a discrepancy of � ��� b et w een the observ ed particle induced bac kground and the predicted pip eline bac k� ground� W e ha v e a substan tial baseline of new dark �bac kground� measuremen ts that ha v e b een in v estigated b y Ha y es �see his pap er in these pro ceedings�� The analysis indicates that the measured bac kground coun t rates are ����� � ����� cts�s�dio de for F OS�BL and ����� � ����� cts�s�dio de for F OS�RD� F or more details on geo� magnetic latitude and longitude dep endence please refer to the ab o v e men tioned pap er in these pro ceedings� These bac kground coun t rates indicate that observ ations of fain t ob jects are a�ected� Summary All F OS observ ations ha v e a particle�induced bac kground subtraction applied to them� ��� Fla t Fields The F OS �at �elds correct for the dio de�to�dio de v ariations on the scale of �� pixels or less� Sp ectral �at �elds are pro duced for all usable F OS detector�ap erture�disp erser com binations� A more complete discussion of �at �elds is giv en in this v olume in a pap er b y Key es� All p ost�COST AR �at �elds ha v e b een deriv ed using the sup er�at tec hnique� F or details of this tec hnique refer to the Instrumen t Science Rep ort CAL�F OS����� Addi� tional v ariations of the sup er�at tec hnique that describ e the curren tly installed p ost� COST AR �at �elds are giv en in Instrumen t Science Rep ort CAL�F OS����� T ypical p ost�COST AR �at �elds displa y deviations of ���� ab out a mean v alue of unit y � but some substan tial ��� � ���� deviations also o ccur� Additional spatial v ariations do o ccur� Details of this in v estigation will b e discussed in a future Instrumen t Science Rep ort� T emp oral v ariations of the F OS�RD G���H� G���H� and G���L �at �elds ha v e b een observ ed� Flat �eld deviations as a function of distance p erp endicular to the disp ersion direction are under in v estigation� A discussion of this is pro vided b y Key es in this v olume� Curren tly � no �at �eld corrections are applied in the pip eline for any paired ap er� ture data� There will b e corrections applied in the pip eline at a later date� Ho w ev er� �at �eld corrections will not b e applied to the ����pair and barred ap ertures� All p ost�COST AR single ap erture high disp ersion data obtained prior to �� July ���� need to b e re�calibrated b ecause pre�COST AR �at �elds w ere used in the pip eline calibration� All p ost�COST AR single ap erture lo w disp ersion data tak en prior to �� June ���� need to b e re�calibrated� All p ost�COST AR �at �elds ha v e b een deliv ered� No �at �eld correc� Summary tions will b e applied to the ����pair and barred ap ertures� Curren tly � no �at �eld cor� rections are applied in the pip eline for an y paired ap erture data� All p ost�COST AR single ap erture high disp ersion data prior to �� July ����� and all p ost�COST AR single ap erture lo w disp ersion data tak en prior to �� June ���� need to b e re� Calibr ating HST� Post Servicing Mission
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