Hubble Space Telescope NICMOS Research Articles

An HST Survey of Protostellar Outflow Cavities: Does Feedback Clear Envelopes?

Abstract We study protostellar envelope and outflow evolution using Hubble Space Telescope NICMOS or WFC3 images of 304 protostars in the Orion molecular clouds. These near-IR images resolve structures in the envelopes delineated by the scattered light of the central protostars with 80 au resolution, and they complement the 1.2 μm to 870 μm spectral energy distributions (SEDs) obtained with the Herschel Orion Protostar Survey program. Based on their 1.60 μm morphologies, we classify the protostars into five categories: nondetections, point sources without nebulosity, bipolar cavity sources, unipolar cavity sources, and irregulars. We find point sources without associated nebulosity are the most numerous, and show through monochromatic Monte Carlo radiative transfer modeling that this morphology occurs when protostars are observed at low inclinations or have low envelope densities. We also find that the morphology is correlated with the SED-determined evolutionary class, with Class 0 protostars more likely to be nondetections, Class I protostars to show cavities, and flat-spectrum protostars to be point sources. Using an edge detection algorithm to trace the projected edges of the cavities, we fit power laws to the resulting cavity shapes, thereby measuring the cavity half-opening angles and power-law exponents. We find no evidence for the growth of outflow cavities as protostars evolve through the Class I protostar phase, in contradiction with previous studies of smaller samples. We conclude that the decline of mass infall with time cannot be explained by the progressive clearing of envelopes by growing outflow cavities. Furthermore, the low star formation efficiency inferred for molecular cores cannot be explained by envelope clearing alone.

ALICE Data Release: A Revaluation of HST-NICMOS Coronagraphic Images

Abstract The Hubble Space Telescope NICMOS instrument was used from 1997 to 2008 to perform coronagraphic observations of about 400 targets. Most of them were part of surveys looking for substellar companions or resolved circumstellar disks to young nearby stars, making the NICMOS coronagraphic archive a valuable database for exoplanets and disks studies. As part of the Archival Legacy Investigations of Circumstellar Environments program, we have consistently reprocessed a large fraction of the NICMOS coronagrahic archive using advanced starlight subtraction methods. We present here the high-level science products of these re-analyzed data, which we delivered back to the community through the Mikulski Archive for Space Telescopes: doi:10.17909/T9W89V. We also present the second version of the HCI-FITS format (for High-Contrast Imaging FITS format), which we developed as a standard format for data exchange of imaging reduced science products. These re-analyzed products are openly available for population statistics studies, characterization of specific targets, or detected point-source identification.

PROBING THE PHYSICAL PROPERTIES OFz= 4.5 LyαEMITTERS WITHSPITZER

We present the results from a stellar population modeling analysis of a sample of 162 z=4.5, and 14 z=5.7 Lyman alpha emitting galaxies (LAEs) in the Bootes field, using deep Spitzer/IRAC data at 3.6 and 4.5 um from the Spitzer Lyman Alpha Survey, along with Hubble Space Telescope NICMOS and WFC3 imaging at 1.1 and 1.6 um for a subset of the LAEs. This represents one of the largest samples of high-redshift LAEs imaged with Spitzer IRAC. We find that 30/162 (19%) of the z=4.5 LAEs and 9/14 (64%) of the z=5.7 LAEs are detected at >3-sigma in at least one IRAC band. Individual z=4.5 IRAC-detected LAEs have a large range of stellar mass, from 5x10^8 to 10^11 Msol. One-third of the IRAC-detected LAEs have older stellar population ages of 100 Myr - 1 Gyr, while the remainder have ages < 100 Myr. A stacking analysis of IRAC-undetected LAEs shows this population to be primarily low mass (8 -- 20 x 10^8 Msol) and young (64 - 570 Myr). We find a correlation between stellar mass and the dust-corrected ultraviolet-based star-formation rate (SFR) similar to that at lower redshifts, in that higher mass galaxies exhibit higher SFRs. However, the z=4.5 LAE correlation is elevated 4-5 times in SFR compared to continuum-selected galaxies at similar redshifts. The exception is the most massive LAEs which have SFRs similar to galaxies at lower redshifts suggesting that they may represent a different population of galaxies than the traditional lower-mass LAEs, perhaps with a different mechanism promoting Lyman alpha photon escape.

DANCING IN THE DARK: NEW BROWN DWARF BINARIES FROM KERNEL PHASE INTERFEROMETRY

This paper revisits a sample of ultracool dwarfs in the Solar neighborhood previously observed with the Hubble Space Telescope's NICMOS NIC1 instrument. We have applied a novel high angular resolution data analysis technique based on the extraction and fitting of kernel phases to archival data. This was found to deliver a dramatic improvement over earlier analysis methods, permitting a search for companions down to projected separations of $\sim$1 AU on NIC1 snapshot images. We reveal five new close binary candidates and present revised astrometry on previously-known binaries, all of which were recovered with the technique. The new candidate binaries have sufficiently close separation to determine dynamical masses in a short-term observing campaign. We also present four marginal detections of objects which may be very close binaries or high contrast companions. Including only confident detections within 19 parsecs, we report a binary fraction of at least $\epsilon_b = 17.2^{+5.7}_{-3.7}%$. The results reported here provide new insights into the population of nearby ultracool binaries, while also offering an incisive case study of the benefits conferred by the kernel phase approach in the recovery of companions within a few resolution elements of the PSF core.

THE TOP 10SPITZERYOUNG STELLAR OBJECTS IN 30 DORADUS

The most luminous Spitzer point sources in the 30 Doradus triggered second generation are investigated coherently in the 3-8 μm region. Remarkable diversity and complexity in their natures are revealed. Some are also among the brightest JHK sources, while others are not. Several of them are multiple when examined at higher angular resolutions with Hubble Space Telescope NICMOS and WFPC2/WFC3 as available, or with VISTA/VMC otherwise. One is a dusty compact H II region near the far northwestern edge of the complex, containing a half-dozen bright I-band sources. Three others appear closely associated with luminous WN stars and causal connections are suggested. Some are in the heads of dust pillars oriented toward R136, as previously discussed from the NICMOS data. One resides in a compact cluster of much fainter sources, while another appears monolithic at the highest resolutions. Surprisingly, one is the brighter of the two extended mystery spots associated with Knot 2 of Walborn et al. Masses are derived from young stellar object models for unresolved sources and lie in the 10-30 M ☉ range. Further analysis of the IR sources in this unique region will advance understanding of triggered massive star formation, perhaps in some unexpected and unprecedented ways.

High resolution near-infrared imaging of submillimeter galaxies

AbstractWe have obtained high-resolution F110W (~ J) and F160W (~ H) band observations of ten submillimeter galaxies (SMGs) with the Hubble Space Telescope's NICMOS camera, in order to resolve their rest-frame optical morphologies, determine the existence of multiple-component, merger-like configurations, and estimate their stellar masses. The selected targets have redshifts in the range 2.2≤ z ≤ 2.81 confirmed with millimeter or mid-IR spectroscopy, guaranteeing that the two bands sample the galaxies' rest-frame optical light with the Balmer break falling between them.

KERNEL PHASE IN FIZEAU INTERFEROMETRY

The detection of high contrast companions at small angular separation appears feasible in conventional direct images using the self-calibration properties of interferometric observable quantities. The friendly notion of closure-phase, which is key to the recent observational successes of non-redundant aperture masking interferometry used with Adaptive Optics, appears to be one example of a wide family of observable quantities that are not contaminated by phase-noise. In the high-Strehl regime, soon to be available thanks to the coming generation of extreme Adaptive Optics systems on ground based telescopes, and already available from space, closure-phase like information can be extracted from any direct image, even taken with a redundant aperture. These new phase-noise immune observable quantities, called kernel-phases, are determined a-priori from the knowledge of the geometry of the pupil only. Re-analysis of archive data acquired with the Hubble Space Telescope NICMOS instrument, using this new kernel-phase algorithm demonstrates the power of the method as it clearly detects and locates with milli-arcsecond precision a known companion to a star at angular separation less than the diffraction limit.

A spatially resolved map of the kinematics, star formation and stellar mass assembly in a star-forming galaxy atz= 4.9

We present a detailed study of the spatially resolved kinematics, star formation and stellar mass in a highly amplified galaxy at z= 4.92 behind the lensing cluster MS 1358+62. We use the observed optical, near- and mid-infrared imaging from Hubble Space Telescope ACS & NICMOS and Spitzer IRAC to derive the stellar mass and the Gemini/NIFS IFU to investigate the velocity structure of the galaxy from the nebular [O ii]λλ3726.8,3728.9 emission. Using a detailed gravitational lens model, we account for lensing amplification factor 12.5 ± 2.0 and find that this intrinsically L* galaxy has a stellar mass of M★= 7 ± 2 × 108 M⊙, a dynamical mass of Mdyn= 3 ± 1 × 109csc2(i) M⊙ (within of 2 kpc) and a star formation rate of 42 ± 8 M⊙ yr−1. The source-plane UV/optical morphology of this galaxy is dominated by five discrete star-forming regions. Exploiting the dynamical information we derive masses for individual star-forming regions of Mcl∼ 108−9 M⊙ with sizes of ∼200 pc. We find that, at a fixed size, the star formation rate density within these H ii regions is approximately two orders of magnitude greater than those observed in local spiral/starburst galaxies, but consistent with the most massive H ii regions in the local Universe such as 30 Doradus. Finally, we compare the spatially resolved nebular emission-line velocity with the Lyα and UV interstellar medium (ISM) lines and find that this galaxy is surrounded by a galactic scale outflow in which the Lyα appears redshifted by ∼150 km s−1 and the UV-ISM lines blueshifted by ∼−200 km s−1 from the (systemic) nebular emission. The velocity structure of the outflow mirrors that of the nebular emission suggesting the outflow is young (≲15 Myr), and has yet to burst out of the system. Taken together, these results suggest that this young galaxy is undergoing its first major epoch of mass assembly.

A surprisingly high pair fraction for extremely massive galaxies at z ∼ 3 in the GOODS NICMOS survey

Abstract We calculate the major pair fraction and derive the major merger fraction and rate for 82 massive (M* &amp;gt; 1011 M⊙) galaxies at 1.7 &amp;lt; z &amp;lt; 3.0 utilizing deep Hubble Space Telescope NICMOS data taken in the GOODS north and south fields. For the first time, our NICMOS data provide imaging with sufficient angular resolution and depth to collate a sufficiently large sample of massive galaxies at z &amp;gt; 1.5 to reliably measure their pair fraction history. We find strong evidence that the pair fraction of massive galaxies evolves with redshift. We calculate a pair fraction of fm= 0.29 ± 0.06 for our whole sample at 1.7 &amp;lt; z &amp;lt; 3.0. Specifically, we fit a power-law function of the form fm=f0(1 +z)m to a combined sample of low-redshift data from Conselice et al. (2007) and recently acquired high-redshift data from the GOODS NICMOS survey. We find a best fit to the free parameters of f0= 0.008 ± 0.003 and m= 3.0 ± 0.4. We go on to fit a theoretically motivated Press–Schechter curve to this data. This Press–Schechter fit, and the data, shows no sign of levelling off or turning over, implying that the merger fraction of massive galaxies continues to rise with redshift out to z∼ 3. Since previous work has established that the merger fraction for lower mass galaxies turns over at z∼ 1.5–2.0, this is evidence that higher mass galaxies experience more mergers earlier than their lower mass counterparts, i.e. a galaxy assembly downsizing. Finally, we calculate a merger rate at z= 2.6 of ℜ &amp;lt; 5 × 105 Gpc-3 Gyr-1, which experiences no significant change to ℜ &amp;lt; 1.2 × 105 Gpc-3 Gyr-1 at z= 0.5. This corresponds to an average M* &amp;gt; 1011 M⊙ galaxy experiencing 1.7 ± 0.5 mergers between z= 3 and 0.

Galactic Bulges fromHubble Space TelescopeNICMOS Observations: Central Galaxian Objects, and Nuclear Profile Slopes

We have measured the structural properties for a sample of S0-Sbc galaxies down to scales of similar to 10 pc using Hubble Space Telescope NICMOS images. Central star clusters are found in 58% of our sample. Their near-infrared luminosities scale with the host bulge luminosities, as reported in 2003 by Balcells and coworkers. In terms of photometric masses, the relation is M-PS = 10(7.75 +/- 0.15) (M-bul/10(10) M-circle dot)(0.76 +/- 0.13). Put together with recent data on bulges hosting supermassive black holes, we infer a nonlinear dependency of the central massive object'' mass on the host bulge mass such that M-CMO/M-circle dot = 10(7.51 +/- 0.06)(M-bul/10(10)M(circle dot))(0.84 +/- 0.06). The linear relation presented by Ferrarese and co-workers may be biased at the low-mass end by the inclusion of the disk light from cluster lenticular galaxies. Bulge-disk decompositions reaching to the outer disk show that similar to 90% of our galaxies possess light excesses that can be modeled with an inner exponential and/or an unresolved source. All the extended nuclear components, with sizes of a few hundred parsecs, have disky isophotes, which suggest that they may be inner disks, rings, or bars; their colors are redder than those of the underlying bulge, arguing against a recent origin for their stellar populations. Surface brightness profiles ( of the total galaxy light, and the bulge component on its own) rise inward to the resolution limit of the data, with a continuous distribution of logarithmic slopes from the low values typical of dwarf ellipticals (0.1

Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition

We present the results of a Hubble Space Telescope NICMOS imaging survey of 22 T-type field brown dwarfs. Five are resolved as binary systems with angular separations of 0.05-0.35, and companionship is established on the basis of component F110W - F170M colors (indicative of CH_4 bsorption) and low probabilities of background contamination. Prior ground-based observations show 2MASS 1553+1532AB to be a common proper-motion binary. The properties of these systems—low multiplicity fraction (12^(+7)_(-4)% resolved, as corrected for sample selection biases), close projected separations (ρ = 1.8-5.0 AU) and near-unity mass ratios—are consistent with previous results for field brown dwarf binaries. Three of the binaries have components that span the poorly understood transition between L dwarfs and T dwarfs. Spectral decomposition analysis of one of these, SDSS 1021-0304AB, reveals a peculiar flux reversal between its components, as its cooler T5 secondary is ~30% brighter at 1.05 and 1.27 μm than its T1 primary. This system, 2MASS 0518-2828AB, and SDSS 1534+1615AB all demonstrate that the J-band brightening observed between late-type L to mid-type T dwarfs is an intrinsic feature of this spectral transition, albeit less pronounced than previously surmised. We also find that the resolved binary fraction of L7 to T3.5 dwarfs is twice that of other L and T dwarfs, an anomaly that can be explained by a relatively rapid evolution of brown dwarfs through the L/T transition, perhaps driven by dynamic (nonequilibrium) depletion of photospheric condensates.

The link between submillimetre galaxies and luminous ellipticals: near-infrared IFU spectroscopy of submillimetre galaxies

We present two-dimensional spectroscopy covering the rest-frame wavelengths of strong optical emission lines in six luminous submillimetre galaxies (SMGs) at z= 1.3–2.5. Using this near-infrared integral field spectroscopy together with Hubble Space Telescope ACS and NICMOS imaging, we map the dynamics and morphologies of these systems on scales from 4–11 kpc. Four of the systems show multiple components in their spatially resolved spectra with average velocity offsets of ∼180 km s−1 across 8 kpc in projection. From the ensemble properties of eight galaxies, from our survey and the literature, we estimate the typical dynamical masses of bright SMGs as 5 ± 3 × 1011 M⊙. This is similar to recent estimates of their stellar masses – suggesting that the dynamics of the central regions of these galaxies are baryon dominated, with a substantial fraction of those baryons in stars by the epoch of observation. Combining our dynamical mass estimates with stellar luminosities for this population, we investigate whether SMGs can evolve on to the Faber–Jackson (FJ) relation for local ellipticals. Adopting a typical lifetime of τburst∼ 300 Myr for the submillimetre-luminous phase – using the latest estimates of gas masses, star formation rates and active galactic nucleus contribution to the bolometric luminosities – we find that the stellar populations of SMGs should fade to place them on the FJ relation, at MK∼−25.1. Furthermore, using the same starburst lifetime we correct the observed space density of SMGs for the duty cycle to derive a volume density of the progenitors of ∼1 × 10−4 Mpc−3. This is consistent with the space density of local luminous early-type galaxies with MK∼−25.1, indicating that SMGs can evolve on to the scaling relations observed for local early-type galaxies, and the observed population at z∼ 2 is then sufficient to account for the formation of the whole population of ≳3 L*K ellipticals seen at z∼ 0.

Improvements to the Image Processing of Hubble Space Telescope NICMOS Observations with Multiple Readouts11Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5‐26555. These observations are associated with programs GO‐8088 and GO‐9075.

ABSTRACTWe report on improvements made to the standard NICMOS processing pipeline. The calculation of the uncertainties on the signal accumulation rate has been modified to include the statistical correlations between the consecutive readouts. This leads to a ∼30% correction in the photometric weight of individual pixels containing faint objects. In order to correct a problem with the existing cosmic‐ray rejection algorithm, we have developed and implemented a joint fit procedure, where the accumulating signal is fit as linear functions of time with the same rate both before and after the cosmic‐ray (CR) impact. This procedure leads to significantly smaller uncertainty in the count rate for pixels affected by CRs. We also show that regions neighboring CRs found by the standard NICMOS pipeline are systematically brighter. This interpixel correlation substantially increases the footprint of CR impacts and is treated for the first time by our new pipeline. The new processing is most relevant for photometry from deep observations of faint targets, for which accurate, optimal, and unbiased uncertainty estimates are important. We present examples of these improvements for deep NIC2 images of a high‐redshift supernova from the Supernova Cosmology Project. The net improvement is a factor of 2 reduction in the number of 3 σ photometric outliers.

Hubble Space Telescope NICMOS Imaging of W3 IRS 5: A Trapezium in the Making?

We present Hubble Space Telescope NICMOS imaging of W3 IRS 5, a binary high-mass protostar. In addition to the two protostars, NICMOS images taken in the F222M and F160W filters show three new 2.22 μm sources with very red colors; these sources fall within a region 5600 AU in diameter and are coincident with an ~100 M☉, dense molecular clump. Two additional point sources are found within 04 (800 AU) of one of the high-mass protostars; these may be stellar companions or unresolved emission knots from an outflow. We propose that these sources constitute a nascent Trapezium system in the center of the W3 IRS 5 cluster containing as many as five proto-OB stars. This would be the first identification of a Trapezium still deeply embedded in its natal gas.

Astrometric Discovery of GJ 164B

We discovered a low-mass companion to the M-dwarf GJ 164 with the CCD-based imaging system of the Stellar Planet Survey (STEPS) astrometric program. The existence of GJ 164B was confirmed with Hubble Space Telescope NICMOS imaging observations. A high-dispersion spectral observation in V sets a lower limit of delta m> 2.2 mag between the two components of the system. Based upon our parallax value of 0.082 +/- 0.008, we derive the following orbital parameters: P = 2.04 +/- 0.03 y, a = 1.03 +/- 0.03 AU, and Mtotal = 0.265 +/- 0.020 MSun. The component masses are MA = 0.170 +/- 0.015 MSun and MB = 0.095 +/- 0.015 MSun. Based on its mass, colors, and spectral properties, GJ 164B has spectral type M6-8 V.

Obscured Star Formation in the Central Region of the Dwarf Galaxy NGC 5253

We present Hubble Space Telescope (HST) NICMOS observations (1.1-2.2 μm) and 1.9-4.1 μm spectroscopy of the central region of the dwarf galaxy NGC 5253. The HST NICMOS observations reveal the presence of a nuclear double star cluster separated by 03-04, or 6-8 pc (for a distance d = 4.1 Mpc). The double star cluster, also a bright double source of Paα emission, appears to be coincident with the double radio nebula detected at 1.3 cm. The eastern near-infrared star cluster (C1) is identified with the youngest optical cluster, whereas the western star cluster (C2), although it is almost completely obscured in the optical, becomes the brightest star cluster in the central region of NGC 5253 at wavelengths longer than 2 μm. Both clusters are extremely young, with ages of approximately 3.5 Myr. C2 is more massive than C1 by a factor of 6-20 (MC2 = 7.7 × 105-2.6 × 106 M☉, for a Salpeter initial mass function [IMF] in the mass range 0.1-100 M☉). Analysis of the circumnuclear spectrum excluding C1 and C2, as well as of a number of other near-infrared-selected clusters with a range of (young) ages, suggests that the star formation was triggered across the central regions of the galaxy. We have also modeled the nuclear UV to mid-infrared spectral energy distribution (SED) of NGC 5253 and found that the infrared part is well modeled by a highly obscured (AV = 17 mag) young starburst with a stellar mass consistent with our photometric estimates for C1 and C2. The SED model predicts a moderately bright polycyclic aromatic hydrocarbon (PAH) feature at 3.3 μm that is not detected in our nuclear L-band spectrum. NGC 5253's low metallicity and a top-heavy IMF likely combine to suppress the 3.3 μm PAH emission that is commonly seen in more massive starburst systems.

High-Resolution Near-Infrared Imaging and Polarimetry of Four Proto-Planetary Nebulae

High-resolution near-infrared Hubble Space Telescope (HST) NICMOS (F160W, F222M) images and polarization (2 ?m) observations were made of four bipolar proto?planetary nebulae (PPNs): IRAS 17150-3224, 17441-2411, 17245-3951, and 16594-4656. The first three of these are viewed nearly edge-on, and for the first time the central stars in them are seen. Color maps reveal a reddened torus between the bipolr lobes in the edge-on cases, with bluer lobes. The polarization values are high, with maximum values ranging from 40% to 80%. The polarization patterns are basically centrosymmetric, with some deviations in the low-polarization equatorial regions. For IRAS 17150-3224, circumstellar arcs are seen at 1.6 ?m, along with a newly discovered loop in the equatorial region. Bright caps are seen at the end of the lobes, indicating that they are not open-ended. A distinct point-symmetric pattern is seen in the strengths of the polarization vectors, especially in IRAS 17150-3224. HST NICMOS observations provide a valuable complement to the WFPC2 visible images in deriving the basic structure of bipolar PPNs.

AChandraX‐Ray Study of the Dense Globular Cluster Terzan 5

We report a Chandra ACIS-I observation of the dense globular cluster Terzan 5. The previously known transient low-mass X-ray binary (LMXB) EXO 1745-248 in the cluster entered a rare high state during our 2000 August observation, complicating the analysis. Nevertheless, nine additional sources clearly associated with the cluster are also detected, ranging from LX(0.5-2.5 keV) = 5.6 × 1032 down to 8.6 × 1031 ergs s-1. Their X-ray colors, luminosities, and spectral fitting indicate that five of them are probably cataclysmic variables and four are likely quiescent LMXBs containing neutron stars. We estimate the total number of sources between LX(0.5-2.5 keV) = 1032 and 1033 ergs s-1 as 11.4 by the use of artificial point source tests and note that the numbers of X-ray sources are similar to those detected in NGC 6440. The improved X-ray position allowed us to identify a plausible infrared counterpart to EXO 1745-248 on our 1998 Hubble Space Telescope NICMOS images. This blue star (F110W = 18.48, F187W = 17.30) lies within 02 of the boresighted LMXB position. Simultaneous Rossi X-Ray Timing Explorer spectra, combined with the Chandra spectrum, indicate that EXO 1745-248 is an ultracompact binary system and show a strong broad 6.55 keV iron line and an 8 keV smeared reflection edge.

The [F[CLC]e[/CLC] [CSC]ii[/CSC]] 1.644 Micron Emission in M82 and NGC 253: Is It a Measure of the Supernova Rate?

We present Hubble Space Telescope NICMOS [Fe II] 1.644 μm, Paα (1.87 μm), and continuum images of the starburst galaxies M82 and NGC 253 at an unprecedented spatial resolution. In both galaxies we detect [Fe II] compact sources superposed on a diffuse background in the disk of the galaxies, together with a component above and below the plane of the galaxy. The radio and [Fe II] emissions perpendicular to the disk of M82 show a remarkable similarity to each other, suggesting that both emissions originate in shocks from supernova explosions. We find a spatial correspondence between bright compact [Fe II]–emitting regions and the location of radio supernova remnants (SNRs) for approximately 30%–50% of radio SNRs in M82 and NGC 253. This lack of a one-to-one correspondence, more than being indicative of a different origin for the radio and [Fe II] emission in starbursts, suggests two populations of SNRs: an older population (104 yr), traced by the [Fe II] emission, and a younger population (a few hundred years old), traced by the radio SNRs. We therefore conclude that the [Fe II] emission in starburst galaxies provides a good estimate of the supernova activity. Using our newly determined [Fe II] luminosities (corrected for extinction) of M82 and NGC 253, we reevaluate the calibration of the supernova rate in terms of the [Fe II] luminosity for starburst galaxies.

New Submillimeter Limits on Dust in the 55 Cancri Planetary System

We present new, high-sensitivity submillimeter observations toward 55 Cancri, a nearby G8 star with one, or possibly two, known planetary companion(s). Our 850 μm map, obtained with the Submillimeter Common-User Bolometric Array on the James Clerk Maxwell Telescope, shows three peaks of emission at the 2.5 mJy level in the vicinity of the star's position. However, the observed peaks are 25''-40'' away from the star, and a deep R-band optical image reveals faint point sources that coincide with two of the submillimeter peaks. Thus, we do not find evidence of dust emission spatially associated with 55 Cancri. The excess 60 μm emission detected with the Infrared Space Observatory may originate from one or more of the 850 μm peaks that we attribute to background sources. Our new results, together with the Hubble Space Telescope NICMOS coronagraphic images in the near-infrared, place stringent limits on the amount of dust in this planetary system and argue against the existence of a detectable circumstellar dust disk around 55 Cnc.