Peter Jakobsen

The James Webb Space Telescope

The James Webb Space Telescope (JWST) is a large (6.6 m), cold (<50 K), infrared (IR)-optimized space observatory that will be launched early in the next decade into orbit around the second Earth–Sun Lagrange point. The observatory will have four instruments: a near-IR camera, a near-IR multiobject spectrograph, and a tunable filter imager will cover the wavelength range, 0.6 < ; < 5.0 μ m, while the mid-IR instrument will do both imaging and spectroscopy from 5.0 < ; < 29 μ m.The JWST science goals are divided into four themes. The key objective of The End of the Dark Ages: First Light and Reionization theme is to identify the first luminous sources to form and to determine the ionization history of the early universe. The key objective of The Assembly of Galaxies theme is to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present day. The key objective of The Birth of Stars and Protoplanetary Systems theme is to unravel the birth and early evolution of stars, from infall on to dust-enshrouded protostars to the genesis of planetary systems. The key objective of the Planetary Systems and the Origins of Life theme is to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for the origins of life in those systems. Within these themes and objectives, we have derived representative astronomical observations.To enable these observations, JWST consists of a telescope, an instrument package, a spacecraft, and a sunshield. The telescope consists of 18 beryllium segments, some of which are deployed. The segments will be brought into optical alignment on-orbit through a process of periodic wavefront sensing and control. The instrument package contains the four science instruments and a fine guidance sensor. The spacecraft provides pointing, orbit maintenance, and communications. The sunshield provides passive thermal control. The JWST operations plan is based on that used for previous space observatories, and the majority of JWST observing time will be allocated to the international astronomical community through annual peer-reviewed proposal opportunities.

First results from the Faint Object Camera - SN 1987A

The first images of SN 1987A taken on day 1278 after outburst with the Faint Object Camera on board the Hubble Space Telescope are presented. The supernova is well detected and resolved spatially in three broadband ultraviolet exposures spanning the 1500-3800 A range and in a narrow-band image centered on the forbidden O III 5007 line. Simple uniform disk fits to the profiles of SN 1987A yield an average angular diameter of 170 + or - 30 mas, corresponding to an average expansion velocity of 6000 km/s. The derived broadband ultraviolet fluxes, when corrected for interstellar absorption, indicate a blue ultraviolet spectrum corresponding to a color temperature near 13,000 K. 24 refs.

Intergalactic HeII absorption towards QSO 1157+3143

We report the discovery of a further line of sight allowing detection of He  Lyα absorption by the intergalactic medium. A HST/STIS survey of 32 bright z ∼ 3 quasars selected from the Hamburg Quasar Surveys yielded one detection toward QSO 1157+3143 (z ∼ 3, B � 17). A 10 orbit follow-up spectrum reveals a UV spectrum significantly suppressed by two intervening Lyman limit systems at z = 2.77 and 2.94, but with the continuum flux recovering sufficiently shortward of ∼1700 A to allow study of the He  absorption spectrum in the redshift range 2.75 ≤ z ≤ 2.97. The absorption is characterized by alternating voids and dense filament structures seen in both He  and H . Attempts to model the He  opacity in terms of H  Lyα forest absorption are not successful in the voids, suggesting that He  reionization is not complete between z = 2.77 and 2.97 or that an optically thin Lyman limit system with z ≈ 0.3 is responsible for the additional opacity.

Faint Object Camera imaging and spectroscopy of NGC 4151

We describe ultraviolet and optical imaging and spectroscopy within the central few arcseconds of the Seyfert galaxy NGC 4151, obtained with the Faint Object Camera on the Hubble Space Telescope. A narrowband image including (O III) lambda(5007) shows a bright nucleus centered on a complex biconical structure having apparent opening angle approximately 65 deg and axis at a position angle along 65 deg-245 deg; images in bands including Lyman-alpha and C IV lambda(1550) and in the optical continuum near 5500 A, show only the bright nucleus. In an off-nuclear optical long-slit spectrum we find a high and a low radial velocity component within the narrow emission lines. We identify the low-velocity component with the bright, extended, knotty structure within the cones, and the high-velocity component with more confined diffuse emission. Also present are strong continuum emission and broad Balmer emission line components, which we attribute to the extended point spread function arising from the intense nuclear emission. Adopting the geometry pointed out by Pedlar et al. (1993) to explain the observed misalignment of the radio jets and the main optical structure we model an ionizing radiation bicone, originating within a galactic disk, with apex at the active nucleus and axis centered on the extended radio jets. We confirm that through density bounding the gross spatial structure of the emission line region can be reproduced with a wide opening angle that includes the line of sight, consistent with the presence of a simple opaque torus allowing direct view of the nucleus. In particular, our modelling reproduces the observed decrease in position angle with distance from the nucleus, progressing initially from the direction of the extended radio jet, through our optical structure, and on to the extended narrow-line region. We explore the kinematics of the narrow-line low- and high-velocity components on the basis of our spectroscopy and adopted model structure.

Detectors for the James Webb Space Telescope Near‐Infrared Spectrograph. I. Readout Mode, Noise Model, and Calibration Considerations

We describe how the James Webb Space Telescope (JWST) Near-Infrared Spectrographs (NIRSpec) detectors will be read out, and present a model of how noise scales with the number of multiple nondestructive reads sampling up the ramp. We believe that this noise model, which is validated using real and simulated test data, is applicable to most astronomical near-infrared instruments. We describe some nonideal behaviors that have been observed in engineering-grade NIRSpec detectors, and demonstrate that they are unlikely to affect NIRSpec sensitivity, operations, or calibration. These include a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using real test data, we show that the reset anomaly is (1) very nearly noiseless and (2) can be easily calibrated out. Likewise, we show that large-amplitude RTN affects only a small and fixed population of pixels. It can therefore be tracked using standard pixel operability maps.

Discovery of an optical synchrotron jet in 3C 264

We report the discovery of a new optical synchrotron jet in the radio galaxy 3C 15. This brings to nine the number of known optical synchrotron jets in nearby radio galaxies. The jet is well resolved in both length and width and extends to a projected metric distance of ~5 kpc from the galaxy nucleus. The host galaxy shows complex inner structure, including a dust lane and what appears to be two, or possibly three, emission filaments or arms. On average the optical jet is bluer than the host galaxy by about 0.4 mag. Unlike other galaxies hosting optical jets, the core of the galaxy does not possess a bright, unresolved nucleus, suggesting that the active galactic nucleus is presently inactive or buried in dust. The radio-optical spectral index, αro ~ 1, is the softest yet observed for radio galaxies with optical jets. The observed disturbances in the nuclear regions are indicative of a recent merger or infall possibly resulting in the ejection of material along the jet.

Detection of an ultraviolet and visible counterpart of the NGC 6624 X-ray burster

We have detected, in images taken with the HST FOC, the UV and optical counterpart of the X-ray source 4U 1820-30 in the globular cluster NGC 6624. Astrometric measurements place this object 2 sigma from the X-ray position of 4U 1820-30. The source dominates a far-UV FOC image and has the same flux at 1400 A as was seen through the large IUE aperture by Rich et al. (1993). It has a B magnitude of 18.7 but is not detected in V. It is 0.66 arcsec from the center of NGC 6624, a fact that may change the interpretation of the P-average of the 11 minute binary orbit. The flux drops between 1400 and 4300 A at a rate that is nearly as steep as that of a Rayleigh-Jeans curve. The flux is far too large to come from the neutron star directly but could accord with radiation from a heated accretion disk and/or the heated side of the companion star.

Preliminary analysis of an ultraviolet Hubble Space Telescope faint object camera image of the center of M31

A 5161 s exposure was taken with the FOC on the central 44 arcsec of M31, through a filter centered at 1750 A. Much of the light is redleak from visible wavelengths, but nearly half of it is genuine UV. The image shows the same central peak found earlier by Stratoscope, with a somewhat steeper dropoff outside that peak. More than 100 individual objects are seen, some pointlike and some slightly extended. We identify them as post-asymptotic giant branch stars, some of them surrounded by a contribution from their accompanying planetary nebulae. These objects contribute almost a fifth of the total UV light, but fall far short of accounting for all of it. We suggest that the remainder may result from the corresponding evolutionary tracks in a population more metal-rich than solar.

Imaging of four planetary nebulae in the Magellanic Clouds using the Hubble Space Telescope Faint Object Camera

Using the Faint Object Camera on-board the Hubble Space Telescope, we have obtained images of four planetary nebulae (PNe) in the Magellanic Clouds, namely N2 and N5 in the SMC and N66 and N201 in the LMC. Each nebula was imaged through two narrow-band filters isolating forbidden O III 5007 and H-beta, for a nominal exposure time of 1000 s in each filter. In forbidden O III, SMC N5 shows a circular ring structure, with a peak-to-peak diameter of 0.26 arcsec and a FWHM of 0.35 arcsec while SMC N2 shows an elliptical ring structure with a peak-to-peak diameter of 0.26 x 0.21. The expansion ages corresponding to the observed structures in SMC N2 and N5 are of the order of 3000 yr. LMC N201 is very compact, with a FWHM of 0.2 arcsec in H-beta. The Type I PN LMC N66 is a multipolar nebula, with the brightest part having an extent of about 2 arcsec and with fainter structures extending over 4 arcsec.

First results from the Faint Object Camera : high-resolution observations of the central object R136 in the 30 Doradus nebula

R136 is the luminous central object of the giant H II region 30 Doradus in the Large Magellanic Cloud. We report on the first high-resolution observations of R136 with the Faint Object Camera on board the Hubble Space Telescope. The physical nature of the brightest component R136a has been a matter of some controversy over the last few years. The UV images obtained show that R131a is a very compact star cluster consisting of more than eight stars within 0″.7 diameter. From these high-resolution images a mass upper limit can be derived for the most luminous stars observed in R136