We have produced an atlas of Spitzer Infrared Spectrograph (IRS) spectra of mass-losing, evolved stars in the Large Magellanic Cloud. These stars were selected to have high mass-loss rates and so contribute significantly to the return of processed materials to the ISM. Our high-quality spectra enable the determination of the chemistry of the circumstellar envelope from the mid-IR spectral features and continuum. We have classified the spectral types of the stars and show that the spectral types separate clearly in infrared color-color diagrams constructed from 2MASS data and synthetic IRAC/MIPS fluxes derived from our IRS spectra. We present diagnostics to identify and classify evolved stars in nearby galaxies with high confidence levels using Spitzer and 2MASS photometry. Comparison of the spectral classes determined using IRS data with the IR types assigned based on NIR colors also revealed a significant number of mis-classifications and enabled us to refine the NIR color criteria resulting in more accurate NIR color classifications of dust-enshrouded objects.

We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of highly luminous, compact mid-infrared sources in the Large Magellanic Cloud. Sources were selected on the basis of infrared colors and 8 micron (MSX) fluxes indicative of highly evolved, intermediate- to high-mass stars with current or recent mass loss at large rates. We determine the chemistry of the circumstellar envelope from the mid-IR continuum and spectral features and classify the spectral types of the stars. In the sample of 60 sources, we find 21 Red Supergiants (RSGs), 16 C-rich Asymptotic Giant Branch (AGB) stars, 11 HII regions, 4 likely O-rich AGB stars, 4 Galactic O-rich AGB stars, 2 OH/IR stars, and 2 B[e] supergiants with peculiar IR spectra. We find that the overwhelming majority of the sample AGB stars (with typical IR luminosities ~1.0E4 L_sun) have C-rich envelopes, while the O-rich objects are predominantly luminous RSGs with L_IR ~ 1.0E5 L_sun. We determine mean bolometric corrections to the stellar K-band flux densities and find that for carbon stars, the bolometric corrections depend on the infrared color, whereas for RSGs, the bolometric correction is independent of IR color. Our results reveal that objects previously classified as PNe on the basis of IR colors are in fact compact HII regions with very red IRS spectra that include strong atomic recombination lines and PAH emission features. We demonstrate that the IRS spectral classes in our sample separate clearly in infrared color-color diagrams that use combinations of 2MASS data and synthetic IRAC/MIPS fluxes derived from the IRS spectra. On this basis, we suggest diagnostics to identify and classify, with high confidence levels, IR-luminous evolved stars and HII regions in nearby galaxies using Spitzer and near-infrared photometry.

We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS ) spectra of highly luminous, compact mid-infrared sources in the Large Magellanic Cloud. Sources were selected on the basis of infrared colors and 8 μm (MSX ) fluxes indicative of highly evolved, intermediateto high-mass stars with current or recent mass loss at large rates. We determine the chemistry of the circumstellar envelope from the mid-IR continuum and spectral features and classify the spectral types of the stars. In the sample of 60 sources, we find 21 Red Supergiants (RSGs), 16 C-rich Asymptotic Giant Branch (AGB) stars, 11 H II regions, 4 likely O-rich AGB stars, 4 Galactic O-rich AGB stars, 2 OH/IR stars, and 2 B[e] supergiants with peculiar IR spectra. We find that the overwhelming majority of the sample AGB stars (with typical IR luminosities ∼ 10 L⊙) have C-rich envelopes, while the O-rich objects are predominantly luminous RSGs with LIR ∼ 10 5 L⊙. For both classes of evolved star (C-rich AGB stars and RSGs), we use the nearto mid-infrared spectral energy distributions to determine mean bolometric corrections to the stellar K-band flux densities. For carbon stars, the bolometric corrections depend on the infrared color, whereas for RSGs, the bolometric correction is independent of IR color. Our results reveal that objects previously classified as PNe on the basis of IR colors are in fact compact H II regions with Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester NY 14623. Email: clbsps,jhk@cis.rit.edu Department of Physics & Astronomy, University of Rochester, Bausch & Lomb Hall, P.O. Box 270171, Rochester, NY 14627-0171 Dept. of Physics and Astronomy, Valparaiso University, Valparaiso, IN 46383 NASA/JPL, 4800 Oak Grove Drive, Pasadena, CA 91109 Air Force Research Laboratory; OASD (NII) Space Programs, Suite 7000, 1851 S. Bell St., Arlington, VA 22202 Valdosta University, 1500 N Patterson Street, Valdosta, GA 31698

Medium- and high-resolution spectroscopy of U Equulei from 1 to 4 μm during 1997-2003 has revealed information about its unusual circumstellar envelope, observed previously at optical and radio wavelengths. Strong absorption bands of H2O and of CO dominate the 1-4 μm spectrum. The gas has a mean temperature of 600 K, and 12C/13C ≤ 10. The CO 2-0 line profiles and velocities imply no net ejection or infall, and indicate either rapid radial gas motions being seen along a narrow continuum beam or absorption by orbiting gas that is nearly coincident with a highly extended continuum source. The gas could be located in a disklike structure. The observed high column densities of warm CO and H2 normally would be associated with sufficient dust to completely obscure the star at optical wavelengths. The observations thus indicate either a highly abnormal gas-to-dust ratio, consistent with the earlier optical observation of abundant refractory metal oxides in the circumstellar gas, or peculiar geometry and/or illumination.

Stars with masses in the range 1–8 solar masses (M⊙) live ordinary lives for ∼109–1010 years, but die extraordinary deaths. First, during their death throes as asymptotic giant branch (AGB) stars they eject, over 104–105 years, half or more of their mass in slowly expanding, spherical winds, and then, in a short (a few 100–1,000 years) and poorly understood phase, they are transformed into aspherical planetary nebula. Recent studies support the idea that high-speed, jet-like flows play a crucial role in this transformation1. Evidence for such outflows is indirect, however; this phase is so short that few nearby stars are likely to be caught in the act. Here we report the discovery of a newly launched, high-speed jet-like outflow in the nearby AGB star, V Hydrae. We have detected both proper motions and ongoing evolution in the jet. These results support a model in which the jet is driven by an accretion disk around an unseen, compact companion. We also find a central, dense equatorial disk-like structure which may enable and/or enhance the formation of the accretion disk.

The Hipparcos parallaxes of cool giants are utilized in two ways in this paper. First, a plot of reduced parallaxes of stars brighter than 6.5, as a function of spectral type, for the first time separates members of the clump from stars in the main giant ridge. A slight modification of the MK luminosity standards has been made so that luminosity class IIIb defines members of the clump, and nearly all of the class III stars fall within the main giant ridge. Second, a new calibration of MK luminosity classes III and IIIb in terms of visual absolute magnitudes has been made.

We report systematic observations of millime- ter CO emission from a sample of 109 oxygen{rich evolved stars (AGB and supergiants), colour{selected from the IRAS Point Source Catalog (0:69 200). In most cases, the ob- served spread in the values of this ratio can be explained by a large range of luminosities. This leads to a new crite- rion to identify AGB stars: an object withR < 150 must have a low mass progenitor. Here we study the correlations between R and vari- ous physical properties of the sources. Most sources with high values of R also have low galactic latitudes, small IRAS variability indices, and early spectral types (typi- cally M1{M5). Conversely, there is no dependence on the IRAS colours, nor on the intensity of silicate 10 me mis- sion. However, a few AGB stars exhibit large R ;o ther factors than luminosity are required to explain these val- ues. Dierent hypotheses, such as the possible presence of a chromosphere, a low 12 C abundance or a variable mass{ loss rate, are examined. Considering the global high OH detection rate ( 67%), we studied the correlations with CO and OH emission. The detection of OH seems to be a useful discriminator of mechanisms that enhanceR.

Every year, an increasing amount of radio-frequency (RF) spectrum in the VHF, UHF, and microwave bands is being utilized to support new commercial and military ventures, and all have the potential to interfere with radio astronomy observations. Such services already cause problems for radio astronomy even in very remote observing sites, and the potential for this form of light pollution to grow is alarming. Preventive measures to eliminate interference through FCC legislation and ITU agreements can be effective; however, many times this approach is inadequate and interference excision at the receiver is necessary. Conventional techniques such as RF filters, RF shielding, and postprocessing of data have been only somewhat successful, but none has been sufficient. Adaptive interference cancellation is a realtime approach to interference excision that has not been used before in radio astronomy. We describe here, for the first time, adaptive interference cancellation in the context of radio astronomy instrumentation, and we present initial results for our prototype receiver.In the 1960s, analog adaptive interference cancelers were developed that obtain a high degree of cancellation in problems of radio communications and radar. However, analog systems lack the dynamic range, noised performance, and versatility required by radio astronomy. The concept of digital adaptive interference cancellation was introduced in the mid-1960s as a way to reduce unwanted noise in low-frequency (audio) systems. Examples of such systems include the canceling of maternal ECG in fetal electrocardiography and the reduction of engine noise in the passenger compartments of automobiles. These audio-frequency applications require bandwidths of only a few tens of kilohertz. Only recently has highspeed digital filter technology made high dynamic range adaptive canceling possible in a bandwidth as large as a few megahertz, finally opening the door to application in radio astronomy.We have built a prototype adaptive canceler that consists of two receivers: the primary channel (input from the main beam of the telescope) and a separate reference channel. The primary channel receives the desired astronomical signal corrupted by RFI (radio-frequency interference) coming in the sidelobes of the main beam. A separate reference antenna is designed to receive only the RFI. The reference channel input is processed using a digital adaptive filter and then subtracted from the primary channel input, producing the system output. The weighting coefficients of the digital filter are adjusted by way of an algorithm that minimizes, in a least-squares sense, the power output of the system. Through an adaptive-iterative process, the canceler locks onto the RFI, and the filter adjusts itself to minimize the effect of the RFI at the system output. We have designed the adaptive canceler with an intermediate frequency (IF) of 40 MHz. This prototype system will ultimately be functional with a variety of radio astronomy receivers in the microwave band. We have also built a prototype receiver centered at 100 MHz (in the FM broadcast band) to test the adaptive canceler with actual interferers, which are well characterized. The initial laboratory tests of the adaptive canceler are encouraging, with attenuation of strong frequency-modulated (FM) interference to 72 dB (a factor of more than 10 million), which is at the performance limit of our measurements. We also consider requirements of the system and the RFI environment for effective adaptive canceling.

A total of 18 image intensified CCD detectors were deployed at 6 locations (two in Negev Desert, Israel, and one in each of the Canary Islands, Long Key in Florida, Haleakala in Hawaii, and the Kwajalein Atoll) to provide a real-time reporting system, as well as data for subsequent detailed analysis, for the 1999 Leonid shower. Fields of view ranged from 9 to 34 degrees, with apparent limiting stellar magnitudes from about +7 to +9. In addition, a dual frequency (29.850 and 38.15 MHz) automated meteor radar with directional determination capability was located in the Canadian Arctic at Alert, Nunavut and provided continuous monitoring of the shower from a location where the radiant was constantly above the horizon. Both the radar and electro-optical systems successfully recorded the activity of the shower in real time, and typical real-time activity plots are presented. Post-event analysis has concentrated on the Israel electro-optical wide field cameras and the time interval centered around the peak of the storm. About 2700 meteors have been digitized, with 680 measured for this analysis. Of these 371 were well enough determined to permit a single-station technique to yield approximate heights. Light curves and photometric masses were computed for these 371 Leonids which form the basis of the preliminary results reported in this paper. These cameras recorded Leonid meteors with peak luminosity in the magnitude range -3 to +5, corresponding to the photometric mass range 10(-4) to 10(-7) kg. A regression plot of photometric mass with magnitude did not indicate any change in light curve shape over the interval studied here. The peak flux as determined by the electro-optical observations was 1.6 +/- 0.1 Leonid meteors of magnitude +6.5 or brighter falling on a one square kilometer area (oriented perpendicular to the Leonid radiant) per hour. This peak flux occurred at approximately 2:07 +/-: 06 UT on Nov 18 1999, corresponding to solar longitude lambda (o) = 235.248 (epoch 2000.0). The radar results were consistent with this maximum flux rate and time. There was not a strong change in mass distribution over the few hours around maximum, although there is some indication that the peak interval was stronger in fainter meteors. Height histograms are provided for beginning, maximum luminosity and ending heights. It was found that maximum luminosity and ending heights were completely independent of mass, consistent with a dustball model in which the meteoroids are fragmented into constituent grains prior to ablation of the grains. However, the beginning height increases sharply (9.1 km per decade of photometric mass change) with increasing mass. This is possibly indicative of a volatile component which ablates early in the atmospheric trajectory.

We report systematic observations of millimeter CO emission from a sample of 109 oxygen-rich evolved stars (AGB and supergiants), colour-selected from the IRAS Point Source Catalog (0.69 < S-25 mu m/S-12 mu m < 1.20). CO(1-0) has been searched with good sensitivity in 81 sources (74% of the sample). CO(1-0) is detected in 54 sources and a significant upper limit has been achieved in 27 sources.In our previous paper we reported on the statistical results of these observations. We showed that in almost 50% of the sources, the ratio of the IRAS 60 mu m flux to CO intensity, R = S-60/T-mb(1-0), is larger by a factor of 3 to more than 10 than what is expected according to the correlation found by Nyman et al. (1992). Supergiants only exhibit very high values (greater than or similar to 200). In most cases, the observed spread in the values of this ratio can be explained by a large range of luminosities. This leads to a new criterion to identify AGE stars: an object with R < 150 must have a low mass progenitor.Here ave study the correlations between R and carious physical properties of the sources, Most sources with high values of R also have low galactic latitudes, small IRAS variability indices, and early spectral types (typically M1-M5). Conversely there is no dependence on the IRAS colours, nor on the intensity of silicate 10 mu m emission. However, a few AGE stars exhibit large R; other factors than luminosity are required to explain these values. Different hypotheses, such as the possible presence of a chromosphere, a low C-12 abundance or a variable mass-loss rate, are examined. Considering the global high OH detection rate (similar to 67%), we studied the correlations with CO and OH emission. The detection of OH seems to be a useful discriminator of mechanisms that enhance R.

We report the detection of both (J = 1-0) and (J = 2-1) CO emission from the oxygen-rich circumstellar envelope around a carbon star with an oxygen-rich circumstellar envelope, BM Gem. The line has two distinct components. Unique among mass-losing carbon stars, there is a feature that is much narrower (FWHM ~ 1 km s-1) than the "normal" CO emission detected from winds. This narrow feature sits on top of a broader (FWHM = 15 km s-1) line, which is probably the emission from the "normal" wind. The most plausible interpretation of the narrow feature is that we are observing emission from a circumbinary reservoir of material, probably in the form of a distorted or puffed-up disk. We propose that this circumbinary reservoir is composed of oxygen-rich material left over from a previous phase of mass loss that was trapped in the system by the action of an as yet undetected companion.

DY Per was confirmed photometrically as an R CrB variable by Alksnis in 1994. Spectra near maximum light show the high-speed ejection of matter (sodium at -174 km/sec in DY Per) characteristic of many of these variable stars. Moderate hydrogen deficiency may also be present. DY Per is remarkable in having a temperature many hundreds of degrees lower than most of the R CrB variables. It is unusual also in not showing clear spectroscopic evidence of high luminosit.

Radial velocities have been measured in a time series of 30 two micron infrared spectra of the bright, carbon-type Mira S Cep. This is the first carbon-rich Mira variable to be examined with time-series, high-resolution, infrared spectroscopy. Velocities were measured by cross correlation of a spectral interval dominated by CN Delta upsilon = -2 red-system lines. The velocities sample the motion of the bulk infrared photosphere and show S Cep to have a typical Mira-type infrared velocity curve with amplitude of 22 km s(-1). The velocities of the cores of low-excitation CO Delta upsilon = 2 lines were also measured. These strong lines show a contribution to the spectrum from material falling into the star well past maximum light. The strong CO lines also have a contribution from material moving away from the star at a few km s(-1). The visual spectrum shows typical characteristics of Mira behavior with Her varying in strength and large differences among atomic line velocities. (C) 1996 American Astronomical Society.

We have compiled a moderate-resolution spectral atlas to aid in the classification of carbon stars on the 1993 Revised MK system of Keenan as refined and extended by the present work. The main purpose of this atlas is to permit rapid and reasonably accurate comparison of the properties of carbon stars in the solar neighborhood with those in the Galactic bulge, the Magellanic Clouds, and other nearby external systems. The classification scheme employed makes no assumptions about evolutionary status of the stars but is based entirely on observable criteria. Spectra of 39 stars are presented in detail, along with a catalog of 119 carbon stars classified according to the Revised MK system.