January 5, 2023
STIS NEWSLETTERS

About This Article

In this STAN we announce the delivery of updated reference files for the second STIS flux recalibration release and a presentation poster detailing these updates at the upcoming winter AAS, new introductory Jupyter Notebooks, and the stenv migration.

Updated STIS Flux Calibration for E230M Echelle Grating

On December 16, 2022 the STIS Team released a set of updated reference files, including STIS throughputs and blaze functions (relative sensitivities across echelle orders) for the NUV/E230M echelle grating. This second release includes updates to the primary modes using central wavelengths 1978 and 2707, as well as the secondary mode using central wavelength of 2415. These new calibration files incorporate both the recent improvements to the stellar atmospheric models (Bohlin et al. 2020, CALSPECv11) and the re-examination of the Vega spectral flux.

The E230M settings provide users with medium resolution echelle spectra covering wavelengths between 1600 and 3100 A. Similar to the previously updated E140M mode, the sensitivity curves and blaze shift coefficients for the E230M modes were derived using observations of the standard DA white dwarf G 191-B2B. The sensitivity curves for these modes were last updated using the CALSPECv7 models (ISR 2012-01). The new CALSPECv11 models increase the NUV fluxes by ~3% at 1700 A, and ~2% at 3000 A. Additionally, the previous version of the NUV photometric throughput table (PHOTTAB) did not flux calibrate order 66 in E230M/2707 (coverage between 3075-3125 A) or order 73 in E230M/2415 (coverage between 2780-2820 A). The updated reference files are now providing standard flux calibrated x1d files which include these additional orders for all post-Servicing Mission 4 (SM4; in 2009) observations.

The recently delivered reference files are replacing the previous versions, and are meant to be used for post-SM4 observations only (see Table 1). Users are reminded that for the G230L and E230M/1978, E230M/2707, and E230M/2415 settings, these newly delivered reference files are updated to the CALSPECv11 models, while the rest of the NUV modes (e.g., G230M, E230H), continue to rely on previous versions of the CALSPEC models. We also note that these new sensitivity files include revisions to the echelle blaze function shift coefficients for these three modes (E230M/1978, E230M/2707, and E230M/2415). The temporal coefficients of the blaze shift were inferred using all of the existing post-SM4 archival observations utilizing these particular modes. To best characterize the evolution of these settings, the team delivered two PHOTTABs and one ripple table (RIPTAB), to be used in the calibration of post-SM4 data. The STIS team is preparing an Instrument Science Report (ISR) describing in detail the creation of the sensitivities and changes to the blaze functions for the E230M settings. As a final note, we remind users that the team has created a Python module, stisblazefix, to help optimize the alignment of the blaze function shifts for individual echelle exposures with the potential to further improve the CALSTIS calibrated products.

The new reference files are available on the HST Calibration Reference Data System (CRDS: https://hst-crds.stsci.edu). All of the STIS observations impacted by these new reference files have now been reprocessed and are available from the HST archive. As usual, we advise users who require the best flux calibration to re-retrieve their observations and verify that their observations have been calibrated with the new reference files listed in Table 1.

Detector Updated Settings Old PHOTTAB Old RIPTTAB New PHOTTAB New RIPTTAB USEAFTER date
NUV-MAMA

E230M/1978

E230M/2707

E230M/2415

64719314o_pht.fits vb816447o_rip.fits 6cg2020mo_pht.fits 6cg2020po_rip.fits MAY 11 2009
        6cg2020oo_pht.fits   MARCH 31 2018

 

Due to the impact these calibration changes have on the quality of the STIS observations, the STIS Team has created and continues to maintain the STIS Flux Recalibration webpage to keep the HST community informed on the status and progress of this effort. For users attending the upcoming 241st AAS Meeting, the STIS Team will be presenting a poster with a detailed update on the absolute flux recalibration effort. Lastly, for any questions regarding these updates, please contact the HST Help Desk

Public Repository of STIS Jupyter Notebooks: Three New Introductory Notebooks

The STIS team has recently begun managing a public Git repository containing a set of Jupyter notebooks to aid the STIS user community with observation planning and data analysis, available here: https://github.com/spacetelescope/STIS-Notebooks.  We are releasing the first three notebooks in a series of introductory notebooks, meant to provide walk-through examples of concepts in our Data Handbook.  These new notebooks cover: (1) how to open and view various types of STIS data, (2) the first steps of the CalSTIS CCD data reduction pipeline, and (3) how to visualize the extraction and background regions when generating x1d data.  More details about each of these notebooks are provided below.  Several more notebooks will be added soon, and we welcome input and suggestions for future notebooks from the community through the HST help desk.  These introductory notebooks join the few specialized notebooks already available in the STIS-Notebooks Git repo, namely the STIS Coronagraphic Visualization Tool and the STIS DrizzlePac Tutorial .  We also provide static rendered versions (html) on the STIS data analysis and software tools website.  We recommend either looking at the rendered version or downloading the notebooks.  If you have any questions, issues or suggestions, please contact the HST help desk.

(1) The ‘view data’ notebook introduces different types of STIS data and shows how to access important information in the fits files.  It covers how to read in and plot the data, handle the data quality flags, visualize a STIS image (example shown in Fig 1), work with TIME-TAG data, and how to access and plot echelle data (example shown in Fig 2). 

echelle
Fig 1: Plot of an example x2d fits file (left).  The view data notebook shows how to read and plot x2d science data.  On the right is the same data but with the pixels marked with a serious data quality flag removed.

spectral orders
Fig 2: Example from the view data notebook showing an image of the flat fielded (flt) echelle data on the left and the 1-D spectrum of all the orders in various colors on the right.​​​​​

(2) The next introductory notebook called ‘calstis_2d_ccd’ provides background for the different calibration steps for the CCD from the raw fits file to the flat fielded (flt) file.  This also shows why there is often negative counts (or flux) values in STIS data.  The six steps and their associated images are shown in Fig 3, which are initializing the data quality array, large scale bias and overscale subtraction, small scale bias subtraction, cosmic ray correction, dark signal subtraction, and flat field correction.

calstis
Fig 3:  The resulting image for each of the six CCD calibration steps presented in the calstis notebook labelled with the names for each calibration switch.

(3) The third public introductory notebook shows how to visualize the 1-D extraction. This is useful for cases where a user may want to do a custom extraction or background subtraction.  The ‘1D_Extraction’ notebook shows how to find the important keywords and plot the extraction and background regions used for the extraction to generate x1d data.  The notebook contains an example with a first order spectrum (Fig 4) and with echelle data.

x1d spectra
Fig 4: An example flt image of first order FUV MAMA G140M data with the extraction region (red) and the background regions (cyan) overplotted that are used to generate the x1d spectrum.

Attendees at the 241st AAS Meeting can hear about these introductory notebooks from Keyi Ding’s presentation Tues, Jan. 10, 2023 2pm PST, session 250.01.

Replacement of Astroconda by stenv, for STScI Software Distribution 

The Space Telescope Science Institute has released “stenv” to supersede Astroconda for its software distribution. stenv provides a common environment for both the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST) pipelines and includes most of the packages in Astroconda.
While Astroconda has served our community well for many years, more recently the vast number of versions with an ever increasing number of software packages would often result in Astroconda taking a very long time to resolve dependencies. Moreover, some Astroconda dependencies are fundamentally incompatible with Python versions >3.7. To better support our users, stenv employs pre-determined Conda environments that are verified compatible with Python versions from 3.8 to 3.11. Additionally, while Astroconda primarily uses Conda recipes to build and serve packages, which need to be updated separately from PyPI releases, stenv draws most of its packages directly from PyPI with pip (though it still requires use of a Conda environment for hstcal and fitsverify, which are provided by conda-forge).

Support for Astroconda will end on February 1st, 2023.


Instructions for installing and using stenv can be found at https://stenv.readthedocs.io/. Questions can be directed to the help desk at hsthelp.stsci.edu.

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