Charles D. Tony Keyes

Spectroscopic observations of H-alpha emission stars from the Stephenson and Stephenson-Sanduleak lists

Spectroscopic observations were obtained for 111 objects from the lists of H-alpha emission stars of Stephenson (1986) and Stephenson and Sanduleak (1977). A total of 26 T Tauri stars, six symbiotic stars, three cataclysmic variables, 17 Be stars, five Me stars, two forbidden BQ stars, two emission-line galaxies, one planetary nebula, and one carbon star with Balmer emission was discovered. Descriptions are given for the spectra of the more unsual objects. A total of 47 objects failed to show emission.

Planning JWST NIRSpec MSA spectroscopy using NIRCam pre-images

The Near-Infrared Spectrograph (NIRSpec) is the work-horse spectrograph at 1-5microns for the James Webb Space Telescope (JWST). A showcase observing mode of NIRSpec is the multi-object spectroscopy with the Micro-Shutter Arrays (MSAs), which consist of a quarter million tiny configurable shutters that are 0. ′′20×0. ′′46 in size. The NIRSpec MSA shutters can be opened in adjacent rows to create flexible and positionable spectroscopy slits on prime science targets of interest. Because of the very small shutter width, the NIRSpec MSA spectral data quality will benefit significantly from accurate astrometric knowledge of the positions of planned science sources. Images acquired with the Hubble Space Telescope (HST) have the optimal relative astrometric accuracy for planning NIRSpec observations of 5-10 milli-arcseconds (mas). However, some science fields of interest might have no HST images, galactic fields can have moderate proper motions at the 5mas level or greater, and extragalactic images with HST may have inadequate source information at NIRSpec wavelengths beyond 2 microns. Thus, optimal NIRSpec spectroscopy planning may require pre-imaging observations with the Near-Infrared Camera (NIRCam) on JWST to accurately establish source positions for alignment with the NIRSpec MSAs. We describe operational philosophies and programmatic considerations for acquiring JWST NIRCam pre-image observations for NIRSpec MSA spectroscopic planning within the same JWST observing Cycle.

Lifetime and Failure Characteristics of Pt/Ne Hollow Cathode Lamps Used as Calibration Sources for UV Space Instruments

We report accelerated aging tests on three Pt/Ne lamps from the same manufacturing run as lamps installed on the Cosmic Origins Spectrograph (COS). One lamp was aged in air at the National Institute of Standards and Technology (NIST) at a current of 10 mA and 50% duty cycle (30 s on, 30 s off) until failure. Two other lamps were aged by the COS instrument development team in a vacuum chamber. Initial radiometrically calibrated spectra were taken of all three lamps at NIST. Calibrated spectra of the air-aged lamp were taken after 206, 500, 778, 783 and 897 hr of operation. Spectra of the vacuum-aged lamps were taken after 500 hr for both lamps, and after 1000 hr for one of the lamps. During vacuum aging, the lamp voltage, photometric stability and temperature were monitored. All three lamps lasted for over 900 hr (100,000 cycles) when run at 10 mA, sufficient for 10-12 years of operation on COS. The total output dropped by less than 15% over 500 hr, with short-term repeatability within a few percent. We recommend that future space operation of these lamps include the lamp voltage in the telemetry as a diagnostic for the lamp aging.

SPECTRAL AND LUMINOSITY CLASSIFICATION OF SYMBIOTIC STAR COOL COMPONENTS WITH NEAR-INFRARED PHOTOMETRY

We have used the absolutely calibrated Wing eight-color near-infrared photometric system to quantitatively derive spectral types and luminosity classes for the cool components of 12 symbiotic stars. We examine the advantages and limitations of the system as applied to symbiotic systems. We find that three systems, CI Cyg, T CrB, and S149, have CN strengths corresponding to luminosity class II. For several systems there is a correlation between photometric phase and measured spectral type.

Commissioning of the cosmic origins spectrograph on the Hubble Space Telescope: an overview of COS servicing mission observatory verification

The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope (HST) during Servicing Mission 4 (SM4) in May 2009. COS is designed to obtain spectra of faint objects at moderate spectral resolution (R > 16,000) in two channels: FUV, covering wavelengths from 1150 to 1450 Å; and NUV, covering 1700 - 3200 Å. Two low resolution gratings (R > 1500) cover the < 900 - 2050 Å (FUV) and 1650 - 3200 Å (NUV) wavelength regions. An imaging capability is also available on the NUV channel. As part of the Hubble Servicing Mission Observatory Verification (SMOV) program, an extensive period of checkout, fine-tuning and preliminary characterization began after the installation of COS. The COS SMOV program was a cooperative effort between the Space Telescope Science Institute and the Instrument Definition Team based at the University of Colorado. Nearly 2800 COS exposures in 34 separate observing programs were obtained during the course of SMOV. Early activities included an initial instrument functional checkout, turn-on and initial characterization of the detectors, NUV and FUV channel focus and alignment, and target acquisition verification and assessment. Once this initial period was completed, science-related calibrations and verifications were performed in order to prepare the instrument for normal science operations. These activities included wavelength calibration, flux calibration, detector flat field characterization, spectroscopic performance verification, high S/N operation, and thermal and structural stability measurements. We discuss the design, execution and results of the SMOV program, including the interrelationships between the various tasks, and how the pre-launch plan was adjusted in real-time due to changing conditions.

Target acquisition for multi-object spectroscopy with JWST NIRSpec

NIRSpec is the flagship spectrograph for JWST in the 0.6 to 5.3 micron wavelength range. Observation with the Micro- Shutter Assembly (MSA) for multiobject spectroscopy (MOS) will use configurable shutters to form spectral slits and provide the first space-based MOS capabilities. The NIRSpec Micro-shutter Assembly Target Acquisition (MSATA) is an autonomous target acquisition scheme to acquire and position targets accurately with respect to the spectral slits. The method uses measured centroid positions of reference stars with accurately known relative positions across the target field for this process. MSATA performs not only linear offsets, but any required telescope orient (roll) correction to remove blind-pointing alignment error. The MSATA procedure can be used for most NIRSpec science and will be a prerequisite for most NIRSpec MOS mode observations. Astrometry relating the positions of science targets and candidate reference stars with a relative accuracy of 5 - 10 mas will be needed to deliver the best calibration accuracy of science sources. With this level of planning accuracy, the MSATA procedure should yield a final total pointing accuracy for NIRSpec MOS targets of <20 mas within the preselected 200 mas-wide MSA shutter. Here we present analysis of test cases using simulated datasets that were used to help define and check operations flow for NIRSpec MSATA.

Observations of Pt/Ne hollow cathode lamps similar to those used on the cosmic origins spectrograph: photometry and vacuum testing

We report accelerated vacuum aging tests on two Pt-Ne lamps identical and/or similar to those installed on the Cosmic Origins Spectrograph (COS) to be installed in the Hubble Space Telescope (HST) in the fall of 2008. One additional lamp was aged in air at the National Institute of Standards and Technology (NIST). All lamps were tested at a 50% duty cycle (30 s on/off) at flight nominal (10 mA) constant current until failure. Calibrated spectra of all lamps were taken at NIST using the 10.7-m normal incidence vacuum spectrograph at various points in the life of the lamps. In this paper we report the results of the photometric, electrical, and thermal monitoring of the vacuum tested lamps, while the spectroscopic and air aging results are given in a companion paper (Nave et al., 2008, SPIE 7011-134). We conclude that the lamps will satisfy the requirements of the HST/COS mission in terms of lifetime, cycles, and thermal and spectral stability.

The COS calibration pipeline and verification process

The Cosmic Origins Spectrograph,1 COS, will be installed in the Hubble Space Telescope (HST) during the next servicing mission. This will be the most sensitive ultraviolet spectrograph ever flown aboard the HST. The calibration pipeline (CALCOS), written in Python, has been developed by the Space Telescope Science Institute (STScI) to support the calibration of HST/COS data. As with other HST pipelines, CALCOS uses an association table to specify the data files to be included, and employs header keywords to specify the calibration steps to be performed and the reference files to be used. CALCOS is designed with a common underlying structure for processing far ultraviolet (FUV) and near ultraviolet (NUV) channels which, respectively, use a cross delay line and a Multi Anode Microchannel Array (MAMA) detector. The pipeline basics and channel dependent specifics are presented. The generation and application of the current reference files, derived from ground-based calibration data, is described, along with the pipeline verification process and results. The CALCOS calibration includes pulse-height filtering and geometric correction for the FUV channel; flat-field, deadtime, and Doppler correction for both channels. Methods for obtaining an accurate wavelength calibra-tion using the on-board spectral line lamp are described. The instrument sensitivity is applied to the background corrected spectrum to produce the final flux calibrated spectrum.

Preliminary calibration results for the HST/cosmic origins spectrograph

We present the preliminary calibration results for the Cosmic Origins Spectrograph, a fourth generation replacement instrument for the Hubble Space Telescope due to be installed in mid-2005. The Cosmic Origins Spectrograph consists of two spectroscopic channels: a far ultraviolet channel that observes wavelengths between 1150 and 2000 Åand a near ultraviolet channel that observes between 1700 and 3200 Å. Each channel supports moderate (R≈20,000) and low (R≈2000) spectral resolution. We discuss the calibration methodology, test configurations, and preliminary end-to-end calibration results. This includes spectral resolution, system efficiency, flat fields, and wavelength scales for each channel. We also present the measured transmission of the Bright Object Aperture (BOA) and the measured spatial resolution.