Kitt Peak National Observatory

Measurements of Hα, H I, and CO distributions in 61 normal spiral galaxies are combined with published far-infrared and CO observations of 36 infrared-selected starburst galaxies, in order to study the form of the global star formation law over the full range of gas densities and star formation rates (SFRs) observed in galaxies. The disk-averaged SFRs and gas densities for the combined sample are well represented by a Schmidt law with index N = 1.4 ± 0.15. The Schmidt law provides a surprisingly tight parametrization of the global star formation law, extending over several orders of magnitude in SFR and gas density. An alternative formulation of the star formation law, in which the SFR is presumed to scale with the ratio of the gas density to the average orbital timescale, also fits the data very well. Both descriptions provide potentially useful "recipes" for modeling the SFR in numerical simulations of galaxy formation and evolution.

We construct dynamical models for a sample of 36 nearby galaxies with Hubble Space Telescope ( HST ) photometry and ground-based kinematics. The models assume that each galaxy is axisymmetric, with a two-integral distribution function, arbitrary inclination angle, a position-independent stellar mass-to-light ratio Υ, and a central massive dark object (MDO) of arbitrary mass M • . They provide acceptable fits to 32 of the galaxies for some value of M • and Υ; the four galaxies that cannot be fitted have kinematically decoupled cores. The mass-to-light ratios inferred for the 32 well-fitted galaxies are consistent with the fundamental-plane correlation Υ ∝ L 0.2 , where L is galaxy luminosity. In all but six galaxies the models require at the 95% confidence level an MDO of mass M • ∼ 0.006 M bulge ≡ 0.006Υ L . Five of the six galaxies consistent with M • = 0 are also consistent with this correlation. The other (NGC 7332) has a much stronger upper limit on M • . We predict the second-moment profiles that should be observed at HST resolution for the 32 galaxies that our models describe well. We consider various parameterizations for the probability distribution describing the correlation of the masses of these MDOs with other galaxy properties. One of the best models can be summarized thus: a fraction f ≃ 0.97 of early-type galaxies have MDOs, whose masses are well described by a Gaussian distribution in log ( M • / M bulge ) of mean -2.28 and standard deviation ∼0.51. There is also marginal evidence that M • is distributed differently for "core" and "power law" galaxies, with core galaxies having a somewhat steeper dependence on M bulge .

We present an atlas of the spectral energy distributions (SEDs) of normal, nonblazar, quasars over the whole available range (radio to 10 keV X-rays) of the electromagnetic spectrum. The primary (UVSX) sample includes 47 quasars for which the spectral energy distributions include X-ray spectral indices and UV data. Of these, 29 are radio quiet, and 18 are radio loud. The SEDs are presented both in figures and in tabular form, with additional tabular material published on CD-ROM. Previously unpublished observational data for a second set of quasars excluded from the primary sample are also tabulated. The effects of host galaxy starlight contamination and foreground extinction on the UVSX sample are considered and the sample is used to investigate the range of SED properties. Of course, the properties we derive are influenced strongly by the selection effects induced by quasar discovery techniques. We derive the mean energy distribution (MED) for radio-loud and radio-quiet objects and present the bolometric corrections derived from it. We note, however, that the dispersion about this mean is large (one decade for both the infrared and ultraviolet components when the MED is normalized at the near-infrared inflection). At least part of the dispersion in the ultraviolet may be due to time variability, but this is unlikely to be important in the infrared. The existence of such a large dispersion indicates that the MED reflects only some of the properties of quasars and so should be used only with caution.

We report measurements of Ω M , Ω Λ , and w from 11 supernovae (SNe) at z = 0.36-0.86 with high-quality light curves measured using WFPC2 on the Hubble Space Telescope ( HST ). This is an independent set of high-redshift SNe that confirms previous SN evidence for an accelerating universe. The high-quality light curves available from photometry on WFPC2 make it possible for these 11 SNe alone to provide measurements of the cosmological parameters comparable in statistical weight to the previous results. Combined with earlier Supernova Cosmology Project data, the new SNe yield a measurement of the mass density Ω M = 0.25 (statistical) ± 0.04 (identified systematics), or equivalently, a cosmological constant of Ω Λ = 0.75 (statistical) ± 0.04 (identified systematics), under the assumptions of a flat universe and that the dark energy equation-of-state parameter has a constant value w = -1. When the SN results are combined with independent flat-universe measurements of Ω M from cosmic microwave background and galaxy redshift distortion data, they provide a measurement of w = -1.05 (statistical) ± 0.09 (identified systematic), if w is assumed to be constant in time. In addition to high-precision light-curve measurements, the new data offer greatly improved color measurements of the high-redshift SNe and hence improved host galaxy extinction estimates. These extinction measurements show no anomalous negative E ( B - V ) at high redshift. The precision of the measurements is such that it is possible to perform a host galaxy extinction correction directly for individual SNe without any assumptions or priors on the parent E ( B - V ) distribution. Our cosmological fits using full extinction corrections confirm that dark energy is required with P (Ω Λ > 0) > 0.99, a result consistent with previous and current SN analyses that rely on the identification of a low-extinction subset or prior assumptions concerning the intrinsic extinction distribution.

We report data for I -band surface brightness fluctuation (SBF) magnitudes, ( V - I ) colors, and distance moduli for 300 galaxies. The survey contains E, S0, and early-type spiral galaxies in the proportions of 49 : 42 : 9 and is essentially complete for E galaxies to Hubble velocities of 2000 km s -1 , with a substantial sampling of E galaxies out to 4000 km s -1 . The median error in distance modulus is 0.22 mag. We also present two new results from the survey. (1) We compare the mean peculiar flow velocity (bulk flow) implied by our distances with predictions of typical cold dark matter transfer functions as a function of scale, and we find very good agreement with cold, dark matter cosmologies if the transfer function scale parameter Γ and the power spectrum normalization σ 8 are related by σ 8 Γ -0.5 ≈ 2 ± 0.5. Derived directly from velocities, this result is independent of the distribution of galaxies or models for biasing. This modest bulk flow contradicts reports of large-scale, large-amplitude flows in the ~200 Mpc diameter volume surrounding our survey volume. (2) We present a distance-independent measure of absolute galaxy luminosity, and show how it correlates with galaxy properties such as color and velocity dispersion, demonstrating its utility for measuring galaxy distances through large and unknown extinction.

All 114 objects from the Palomar Bright Quasar Survey (BQS) have been observed using the VLA at 5 GHz (6 cm) wavelength with 18 arcsec resolution. The new radio observations typically reach a level of 0. 1 in the ratio R of radio-to-optical luminosity which allow radio emission to be detected from most of the BQS objects. Ninety six (84%) of the BQS were detected as radio sources above a 3 σ level of 0.2 mJy, and 75 (82%) of the complete sample of 92 quasars with M_B_ < -23 were detected. There appears to be no difference in the radio properties of AGNs (M_B_ > 23) and quasars (M_B_ < 23). The distribution of radio flux density for the BQS sample appears bimodal. Most of the BQS quasars are "radio quiet" and have a radio flux density close to that of the optical flux density, but 15% - 20% are "radio loud" and are much brighter at radio than at optical wavelengths. Only a few percent of the BQS sample overlap radio-selected quasars in the ratio of radio-to-optical flux density. Most of the sources detected with 18 arcsec resolution were reobserved with a resolution of 0.5 arcsec. For the optically selected quasars, we find an increasing fraction of compact sources with increasing redshift. We derive the radio luminosity function, assuming that it is either (a) independent of optical luminosity, or (b) a function of the ratio R of radio-to-optical luminosity. The statistics of radio detections of optically selected quasars in this and in other published studies are equally well represented by the two cases. The radio emission from high-redshift quasars (z > 0.5) is dominated by compact components; quasars with R > 100 mostly have small redshifts. The distinction between the radio-loud and radio-quiet quasars from this optically selected sample cannot be explained simply by the effects of geometry and relativistic beaming for objects having a fixed ratio of intrinsic radio and optical luminosity.

We report data for $I$ band Surface Brightness Fluctuation (SBF) magnitudes, V-I colors, and distance moduli for 300 galaxies. The Survey contains E, S0 and early-type spiral galaxies in the proportions of 49:42:9, and is essentially complete for E galaxies to Hubble velocities of 2000 km/s, with a substantial sampling of E galaxies out to 4000 km/s. The median error in distance modulus is 0.22 mag. We also present two new results from the Survey. (1) We compare the mean peculiar flow velocity (bulk flow) implied by our distances with predictions of typical cold dark matter transfer functions as a function of scale, and find very good agreement with cold, dark matter cosmologies if the transfer function scale parameter $\\Gamma$, and the power spectrum normalization $\\sigma_8$ are related by $\\sigma_8 \\Gamma^{-0.5} \\approx 2\\pm0.5$. Derived directly from velocities, this result is independent of the distribution of galaxies or models for biasing. The modest bulk flow contradicts reports of large-scale, large-amplitude flows in the $\\sim200$ Mpc diameter volume surrounding our Survey volume. (2) We present a distance-independent measure of absolute galaxy luminosity, \\Nbar, and show how it correlates with galaxy properties such as color and velocity dispersion, demonstrating its utility for measuring galaxy distances through large and unknown extinction.

The energy requirements of gamma-ray bursts have in past been poorly constrained because of three major uncertainties: the distances to bursts, the degree of burst beaming, and the efficiency of gamma-ray production. The first of these has been resolved, with both indirect evidence (the distribution of bursts in flux and position) and direct evidence (redshifted absorption features in the afterglow spectrum of GRB 970508) pointing to cosmological distances. We now wish to address the second uncertainty. Afterglows allow a statistical test of beaming, described in an earlier paper. In this paper, we modify a standard fireball afterglow model to explore the effects of beaming on burst remnant dynamics and afterglow emission. If the burst ejecta are beamed into angle ζ m , the burst remnant's evolution changes qualitatively once its bulk Lorentz factor Γ ≲ 1/ζ m : before this, Γ declines as a power law of radius, while afterward, it declines exponentially. This change results in a broken power-law light curve whose late-time decay is faster than expected for a purely spherical geometry. These predictions disagree with afterglow observations of GRB 970508. We explored several variations on our model, but none seems to be able to change this result. We therefore suggest that this burst is unlikely to have been highly beamed and that its energy requirements were near those of isotropic models. More recent afterglows may offer the first practical applications for our beamed models.

Observations of the optical extreme ultraviolet spectrum of the Jupiter planetary system during the Voyager 1 encounter have revealed previously undetected physical processes of significant proportions. Bright emission lines of S III, S IV, and O III indicating an electron temperature of 10(5) K have been identified in preliminary analyses of the Io plasma torus spectrum. Strong auroral atomic and molecular hydrogen emissions have been observed in the polar regions of Jupiter near magnetic field lines that map the torus into the atmosphere of Jupiter. The observed resonance scattering of solar hydrogen Lyman alpha by the atmosphere of Jupiter and the solar occultation experiment suggest a hot thermosphere (>/= 1000 K) wvith a large atomic hydrogen abundance. A stellar occultation by Ganymede indicates that its atmosphere is at most an exosphere.

We investigate the extent to which the Palomar-Green (PG) Bright Quasar Survey (BQS) is complete and representative of the general quasar population by comparing it with imaging and spectroscopy from the Sloan Digital Sky Survey (SDSS). A comparison of SDSS and PG photometry of both stars and quasars reveals the need to apply a color and magnitude recalibration to the PG data. Using the SDSS photometric catalog, we define the PG's parent sample of objects that are not main-sequence stars and simulate the selection of objects from this parent sample using the PG photometric criteria and errors. This simulation shows that the effective U - B cut in the PG survey is U - B < -0.71, implying a color-related incompleteness. As the color distribution of bright quasars peaks near U - B = -0.7 and the 2 σ error in U - B is comparable to the full width of the color distribution of quasars, the color incompleteness of the BQS is approximately 50% and essentially random with respect to U - B color for z < 0.5. There is, however, a bias against bright quasars at 0.5 < z < 1, which is induced by the color-redshift relation of quasars (although quasars at z > 0.5 are inherently rare in bright surveys in any case). We find no evidence for any other systematic incompleteness when comparing the distributions in color, redshift, and FIRST radio properties of the BQS and a BQS-like subsample of the SDSS quasar sample. However, the application of a bright magnitude limit biases the BQS toward the inclusion of objects that are blue in g - i , in particular compared to the full range of g - i colors found among the i -band limited SDSS quasars, and even at i -band magnitudes comparable to those of the BQS objects.

We have obtained moderate resolution ( R = few thousand) spectra of the Na I λλ5890, 5896 (Na D) absorption line in a sample of 32 far-IR-bright starburst galaxies. In 18 cases, the Na D line in the nucleus is produced primarily by interstellar gas, while cool stars contribute significantly in the others. In 12 of the 18 "interstellar-dominated" cases the Na D line is blueshifted by over 100 km s -1 relative to the galaxy systemic velocity (the "outflow sources"), while no case shows a net redshift of more than 100 km s -1 . The absorption-line profiles in these outflow sources span the range from near the galaxy systemic velocity to a maximum blueshift of ∼400-600 km s -1 . The outflow sources are galaxies systematically viewed more nearly face-on than the others. We therefore argue that the absorbing material consists of ambient interstellar material that has been entrained and accelerated along the minor axis of the galaxy by a hot starburst-driven superwind. The Na D lines are optically thick, but indirect arguments imply total hydrogen column densities of N H ∼ few × 10 21 cm -2 . This implies that the superwind is expelling matter at a rate comparable to the star formation rate. This outflowing material is evidently very dusty: we find a strong correlation between the depth of the Na D profile and the line-of-sight reddening. Typical implied values are E ( B - V ) = 0.3-1 over regions several-to-10 kpc in size. We briefly consider some of the potential implications of these observations. The estimated terminal velocities of superwinds inferred from the present data and extant X-ray data are typically 400-800 km -1 , are independent of the galaxy rotation speed, and are comparable to (substantially exceed) the escape velocities for L * (dwarf) galaxies. The resulting selective loss of metals from shallower potential wells can establish the mass-metallicity relation in spheroids, produce the observed metallicity in the intracluster medium, and enrich a general IGM to of order 10 -1 solar metallicity. If the outflowing dust grains can survive their journey into the IGM, their effect on observations of cosmologically distant objects would be significant.

Trigonometric parallax determinations are presented for 28 late type dwarfs and brown dwarfs, including eight M dwarfs with spectral types between M7 and M9.5, 17 L dwarfs with spectral types between L0 and L8, and three T dwarfs. Broadband photometry at CCD wavelengths (VRIz) and/or near-IR wavelengths (JHK) are presented for these objects and for 24 additional late-type dwarfs. Supplemented with astrometry and photometry from the literature, including ten L and two T dwarfs with parallaxes established by association with bright, usually HIPPARCOS primaries, this material forms the basis for studying various color-color and color-absolute magnitude relations. The I-J color is a good predictor of absolute magnitude for late-M and L dwarfs. M_J becomes monotonically fainter with I-J color and with spectral type through late-L dwarfs, then brightens for early-T dwarfs. The combination of zJK colors alone can be used to classify late-M, early-L, and T dwarfs accurately, and to predict their absolute magnitudes, but is less effective at untangling the scatter among mid- and late-L dwarfs. The mean tangential velocity of these objects is found to be slightly less than that for dM stars in the solar neighborhood, consistent with a sample with a mean age of several Gyr. Using colors to estimate bolometric corrections, and models to estimate stellar radii, effective temperatures are derived. The latest L dwarfs are found to have T_eff ~ 1360 K.

We present the results of a speckle interferometric survey made with the CHARA speckle camera and 4 m–class telescopes of Galactic O-type stars with V < 8. We can detect with the speckle camera binaries in the angular separation range 0 035 < ρ < 1 5 with Δ m < 3, and we have discovered 15 binaries among 227 O-type systems. We combined our results on visual binaries with measurements of wider pairs from the Washington Double Star Catalog and fainter pairs from the Hipparcos Catalogue, and we made a literature survey of the spectroscopic binaries among the sample. We then investigated the overall binary frequency of the sample and the orbital characteristics of the known binaries. Binaries are common among O stars in clusters and associations (>59% have a visual or spectroscopic companion) but less so among field and especially runaway stars. There are many triple systems among the speckle binaries, and we discuss their possible role in the ejection of stars from clusters. The period distribution of the binaries is bimodal in log P , but we suggest that binaries with periods of years and decades may eventually be found to fill the gap. The mass ratio distribution of the visual binaries increases toward lower mass ratios, but low mass ratio companions are rare among close, spectroscopic binaries (probably because of the difficulty of spectroscopic detection rather than a real deficit). We present distributions of the eccentricity and longitude of periastron for spectroscopic binaries with elliptical orbits, and we find strong evidence of a bias in the longitude of periastron distribution (the "Barr effect"), which is probably caused by line distortions introduced by circumstellar gas.

Using deep near-infrared and optical observations of the Hubble Deep Field-North from the Hubble Space Telescope NICMOS and WFPC2 instruments and from the ground, we examine the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at 2.0 ≲ z ≲ 3.5 in order to investigate their stellar population properties. The ultraviolet-optical rest-frame SEDs of the galaxies are much bluer than those of present-day spiral and elliptical galaxies and are generally similar to those of local starburst galaxies with modest amounts of reddening. We use stellar population synthesis models to study the properties of the stars that dominate the light from LBGs. Under the assumption that the star formation rate is continuous or decreasing with time, the best-fitting models provide a lower bound on the LBG mass estimates. LBGs with " L *" UV luminosities are estimated to have minimum stellar masses ~10 10 ☉ , or roughly 1/10 that of a present-day L * galaxy, similar to the mass of the Milky Way bulge. By considering the photometric effects of a second stellar population component of maximally old stars, we set an upper bound on the stellar masses that is ~3-8 times the minimum mass estimate. The stellar masses derived for bright LBGs are similar to published estimates of their dynamical masses based on nebular emission line widths, suggesting that such kinematic measurements may substantially underestimate the total masses of the dark matter halos. We find only loose constraints on the individual galaxy ages, extinction, metallicities, initial mass functions, and prior star formation histories. Most LBGs are well fitted by models with population ages that range from 30 Myr to ~1 Gyr, although for models with subsolar metallicities a significant minority of galaxies are well fitted by very young (≲10 Myr), very dusty stellar populations, A (1700 Å) > 2.5 mag. We find no galaxies whose SEDs are consistent with young (≲10 8 yr), dust-free objects, which suggests that LBGs are not dominated by "first-generation" stars and that such objects are rare at these redshifts. We also find that the typical ages for the observed star formation events are significantly younger than the time interval covered by this redshift range (~1.5 Gyr). From this, and from the relative absence of candidates for quiescent, non-star-forming galaxies at these redshifts in the NICMOS data that might correspond to the fading remnants of galaxies formed at higher redshift, we suggest that star formation in LBGs may be recurrent, with short duty cycles and a timescale between star formation events of ≲1 Gyr.

We have studied the relationship between the star formation rate (SFR), surface density, and gas surface density in the spiral galaxy M51a (NGC 5194), using multiwavelength data obtained as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS). We introduce a new SFR index based on a linear combination of Hα emission-line and 24 μm continuum luminosities, which provides reliable extinction-corrected ionizing fluxes and SFR densities over a wide range of dust attenuations. The combination of these extinction-corrected SFR densities with aperture synthesis H I and CO maps has allowed us to probe the form of the spatially resolved star formation law on scales of 0.5-2 kpc. We find that the resolved SFR versus gas surface density relation is well represented by a Schmidt power law, which is similar in form and dispersion to the disk-averaged Schmidt law. We observe a comparably strong correlation of the SFR surface density with the molecular gas surface density, but no significant correlation with the surface density of atomic gas. The best-fitting slope of the Schmidt law varies from N = 1.37 to 1.56, with zero point and slope that change systematically with the spatial sampling scale. We tentatively attribute these variations to the effects of areal sampling and averaging of a nonlinear intrinsic star formation law. Our data can also be fitted by an alternative parameterization of the SFR surface density in terms of the ratio of gas surface density to local dynamical time, but with a considerable dispersion.

A comprehensive study of the measurement of star formation histories from colour-magnitude diagrams (CMDs) is presented, with an emphasis on a variety of subtle issues involved in the generation of model CMDs and maximum likelihood solution. Among these are the need for a complete sampling of the synthetic CMD, the use of proper statistics for dealing with Poisson-distributed data (and a demonstration of why χ2 must not be used), measuring full uncertainties in all reported parameters, quantifying the goodness-of-fit, and questions of binning the CMD and incorporating outside information. Several example star formation history measurements are given. Two examples involve synthetic data, in which the input and recovered parameters can be compared to locate possible flaws in the methodology (none were apparent) and measure the accuracy with which ages, metallicities and star formation rates can be recovered. Solutions of the histories of seven Galactic dwarf spheroidal companions (Carina, Draco, Leo I, Leo II, Sagittarius, Sculptor and Ursa Minor) illustrate the ability to measure star formation histories given a variety of conditions — numbers of stars, complexity of star formation history and amount of foreground contamination. Significant measurements of ancient >8 Gyr star formation are made in all seven galaxies. Sculptor, Draco and Ursa Minor appear entirely ancient, while the other systems show varying amounts of younger stars.

We present results from an optical-infrared photometric study of early-type (E+S0) galaxies in 19 galaxy clusters out to z = 0.9. The galaxy sample is selected on the basis of morphologies determined from Hubble Space Telescope ( HST ) WFPC2 images and is photometrically defined in the K band in order to minimize redshift-dependent selection biases. Using new ground-based photometry in five optical and infrared bands for each cluster, we examine the evolution of the color-magnitude relation for early-type cluster galaxies, considering its slope, intercept, and color scatter around the mean relation. New multiwavelength photometry of galaxies in the Coma Cluster is used to provide a baseline sample at z ≈ 0 with which to compare the distant clusters. The optical-IR colors of the early-type cluster galaxies become bluer with increasing redshift in a manner consistent with the passive evolution of an old stellar population formed at an early cosmic epoch. The degree of color evolution is similar for clusters at similar redshift and does not depend strongly on the optical richness or X-ray luminosity of the cluster, which suggests that the history of early-type galaxies is relatively insensitive to environment, at least above a certain density threshold. The slope of the color-magnitude relationship shows no significant change out to z = 0.9, which provides evidence that it arises from a correlation between galaxy mass and metallicity, not age. Finally, the intrinsic scatter in the optical-IR colors of the galaxies is small and nearly constant with redshift, which indicates that the majority of giant, early-type galaxies in clusters share a common star formation history, with little perturbation due to uncorrelated episodes of later star formation. Taken together, our results are consistent with models in which most early-type galaxies in rich clusters are old, formed the majority of their stars at high redshift in a well-synchronized fashion, and evolved quiescently thereafter. We consider several possible effects that may be introduced by the choice of morphologically recognizable elliptical and S0 galaxies in dense environments as a subject for study. In particular, the inclusion of S0 galaxies, which might be undergoing morphological transformation in clusters as part of the Butcher-Oemler effect, may influence the results of our investigation.

We describe the current plans for a spectroscopic survey of millions of stars in the Milky Way galaxy using the Guo Shou Jing Telescope (GSJT, formerly called the Large sky Area Multi-Object fiber Spectroscopic Telescope — LAMOST). The survey will obtain spectra for 2.5 million stars brighter than r < 19 during dark/grey time, and 5 million stars brighter than r < 17 or J < 16 on nights that are moonlit or have low transparency. The survey will begin in the fall of 2012, and will run for at least four years. The telescope's design constrains the optimal declination range for observations to 10° < δ < 50°, and site conditions lead to an emphasis on stars in the direction of the Galactic anticenter. The survey is divided into three parts with different target selection strategies: disk, anticenter, and spheroid. The resulting dataset will be used to study the merger history of the Milky Way, the substructure and evolution of the disks, the nature of the first generation of stars through identification of the lowest metallicity stars, and star formation through study of open clusters and OB associations. Detailed design of the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) survey will be completed in summer 2012, after a review of the results of the pilot survey.

The CHARA Array is a six 1 m telescope optical/IR interferometric array located on Mount Wilson, California, designed and built by the Center for High Angular Resolution Astronomy of Georgia State University. In this paper we describe the main elements of the Array hardware and software control systems, as well as the data reduction methods currently being used. Our plans for upgrades in the near future are also described.

If gamma-ray bursts are highly collimated, radiating into only a small fraction of the sky, the energy requirements of each event may be reduced by several (~4-6) orders of magnitude, and the event rate is increased correspondingly. Extreme conditions in gamma-ray bursters lead to highly relativistic motions (bulk Lorentz factors of Γ ≳ 100). This results in strong forward beaming of the emitted radiation in the observer's rest frame. Thus, all information on gamma-ray bursts comes from those ejecta emitted in a narrow cone (opening angle of ~1/Γ) pointing toward the observer. We are at present ignorant of whether there are ejecta outside that cone or not. The recent detection of longer wavelength transients following gamma-ray bursts allows an empirical test of whether gamma-ray bursts are well-collimated jets or spherical fireballs. The bulk Lorentz factor of the burst ejecta will decrease with time after the event, as the ejecta sweep up the surrounding medium. Thus, radiation from the ejecta is beamed into an ever-increasing solid angle as the burst remnant evolves. It follows that if gamma-ray bursts are highly collimated, many more optical and radio transients should be observed without associated gamma rays than with them. Published supernova searches may contain enough data to test the most extreme models of gamma-ray beaming. We close with a brief discussion of other possible consequences of beaming, including its effect on the evolution of burst remnants.