The First Orbital Period for a Dwarf Nova in a Globular Cluster: V101 in M5

We report the first orbital period determination for a Dwarf Nova (DN) in a glubular cluster: V101 in M5 has a period of 5.796 +- 0.036 hours. We derived this period from I-band photometry acquired with the Calypso Observatory High Resolution Camera operating with tip-tilt adaptive optics correction. Observations from the South African Astronomical Observatory in the V-band were also analyzed and exhibit a periodic signal of the same period. This orbital period suggests that V101 has a secondary of mid to late K spectral type with Mv = +8.2 +- 0.5. The predicted spectral type is consistent with previous spectral observations in quiescence which show a fairly red continuum. From the observed minimum brightness of V = 22.5, we derive a distance modulus of (m - M)v = 14.3 +- 0.5 to the DN which supports V101's membership in the globular cluster M5. Measurement of the ellipsoidality effect indicates that the orbital plane of the V101 system is moderately inclined, but not enough to exhibit eclipses.Comment: 28 pages, 12 figures, 3 table

Detection of Pre-Shock Dense Circumstellar Material of SN 1978K

The supernova SN 1978K has been noted for its lack of emission lines broader than a few thousand km/s since its discovery in 1990. Modeling of the radio spectrum of the peculiar SN 1978K indicates the existence of HII absorption along the line of sight. To determine the nature of this absorbing region, we have obtained a high-dispersion spectrum of SN 1978K at the wavelength range 6530--6610 \AA. The spectrum shows not only the moderately broad H-alpha emission of the supernova ejecta but also narrow nebular H-alpha and [N II] emission. The high [N II]6583/H-alpha ratio, 0.8-1.3, suggests that this radio absorbing region is a stellar ejecta nebula. The expansion velocity and emission measure of the nebula are consistent with those seen in ejecta nebulae of luminous blue variables. Previous low-dispersion spectra have detected a strong [N II]5755 line, indicating an electron density of 3-12x10^5 cm^{-3}. We argue that this stellar ejecta nebula is probably part of the pre-shock dense circumstellar envelope of SN 1978K. We further suggest that SN 1997ab may represent a young version of SN 1978K.Comment: 12 pages, 1 figure, accepted for publication in the ApJ Letter

Discovery of an M8.5 Dwarf With Proper Motion mu=2.38 arcsec/yr

We report the discovery of LSR1826+3014, a very faint (V=19.36) star with a very large proper motion (mu=2.38 arcsec/yr). A low resolution red spectrum reveals that LSR1826+3014 is an ultra-cool red dwarf with spectral type M8.5 V and with a radial velocity v_rad=+77+/-10 km/s. LSR1826+3014 is thus the faintest red dwarf ever discovered with a proper motion larger than 2 arcsec/yr. Optical and infrared photometry suggest that the star is at a distance d=13.9+/-3.5 pc from the Sun, which implies it is moving relative to the local standard of rest with a total velocity of 175+/-25 km/s. Numerical integration of its orbit suggests that LSR1826+3014 is on a halo-like galactic orbit.Comment: 12 pages, including 1 table and 3 figures, accepted for publication in The Astrophysical Journal Letter

Spitzer 24 um Images of Planetary Nebulae

Spitzer MIPS 24 um images were obtained for 36 Galactic planetary nebulae (PNe) whose central stars are hot white dwarfs (WDs) or pre-WDs with effective temperatures of ~100,000 K or higher. Diffuse 24 um emission is detected in 28 of these PNe. The eight non-detections are angularly large PNe with very low H-alpha surface brightnesses. We find three types of correspondence between the 24 um emission and H-alpha line emission of these PNe: six show 24 um emission more extended than H-alpha emission, nine have a similar extent at 24 um and H-alpha, and 13 show diffuse 24 um emission near the center of the H-alpha shell. The sizes and surface brightnesses of these three groups of PNe and the non-detections suggest an evolutionary sequence, with the youngest ones being brightest and the most evolved ones undetected. The 24 um band emission from these PNe is attributed to [O IV] 25.9 um and [Ne V] 24.3 um line emission and dust continuum emission, but the relative contributions of these three components depend on the temperature of the central star and the distribution of gas and dust in the nebula.Comment: 24 pages, 8 figures, to appear in the Astronomical Journal, September issue. Relace previous file; two references are added and typos are correcte

Imaging and Spectroscopy of Damped Lyα Quasi-Stellar Object Absorption-Line Clouds

We present the results of a multifaceted search for line emission from the vicinities of high-redshift quasi-stellar object (QSO) absorption-line clouds, most of them damped Lyα systems at z ≳ 2. Seven fields containing QSOs with known intervening damped Lyα absorbers were imaged with the GSFC Fabry-Perot Imager to search for diffuse redshifted Lyα. Apart from the one Lyα companion galaxy reported previously, no confirmed extended Lyα emission was detected down to 3 σ flux levels of around 3 x 10-17 ergs s-1 cm-2, corresponding to star formation rates ≲1 M⊙ yr-1, assuming case B recombination, a reasonable initial mass function, and negligible extinction by dust. One of the damped Lyα systems studied here, toward Q0836+113, has been reported to show faint, extended Lyα emission. While our Lyα images of that field are not sensitive enough to confirm the reported flux levels, we did detect and spectroscopically confirm redshifted [O II] λ3727 and continuum emission from a closer intervening system, a Mg II system at z = 0.788, at the same spatial position as the reported Lyα emission from the more distant object, and we suggest the possibility that all the observations of this field can be explained by the closer system alone. Six damped Lyα systems, including two that were imaged with the Fabry-Perot, were also imaged with two-dimensional long-slit CCD spectroscopy at ∼2 Å resolution in the core of the Lyα absorption line. No convincing Lyα emission was found from any of the systems, including Q0836+113, for which our sensitivity was again insufficient to confirm the previously reported extended Lyα emission. However, there is yet another independent claim of Lyα emission from that cloud, but spatially unresolved, in conflict with the report of extended emission; our observations do not reproduce the report of compact Lyα emission, which should have appeared at about the 7 σ level. Although observationally allowable quantities of dust in the damped Lyα clouds can in some cases quench Lyα flux by up to several orders of magnitude, several of the damped clouds studied here are arguably metal and dust poor, leading us to believe that our limits on Lyα emission generally constrain the star formation rates to be ≲10 M⊙ yr-1, comparable to normal Sc galaxies today. Whatever their exact nature, the damped Lyα clouds therefore appear not to be spectacular primeval galaxies seen in the act of forming a galaxy\u27s worth of stars

Discovery of a Lyα Galaxy Near a Damped Lyα Absorber at z = 2.3

We report the detection of a galaxy associated with the damped Lyα absorbing cloud seen at z = 2.309 toward the QSO PHL 957 (zem = 2.681). The galaxy was discovered in deep Fabry-Perot narrow-band CCD frames and was subsequently imaged spectroscopically. In addition to a strong but narrow Lyα emission line (FLyα = 5.6 × 10-16 ergs s-1 cm-2, FWHM ∼ 700 km s-1) and weaker C IV and He II lines, the object shows continuum at V ∼ 24, with a slope (in Fν) rising slightly toward the red, similar to what is seen in high-redshift radio galaxies; however, the galaxy does not correspond to any known radio source in the literature. The detected emission lines and continuum are most easily interpreted as light from hot, recently formed stars, implying not only a sizable star formation rate (SFR ≥ 5 M⊙ yr-1) but also a scarcity of dust, which readily quenches Lyα photons. The emission region appears to be marginally resolved spatially and is located 48 to the NW of the QSO, corresponding to a projected distance of 270h-1 kpc (for q0 = 0.1); the velocity difference with respect to the damped Lya cloud is ∼350 km s-1. The spatial correlation of the absorbing cloud and the companion galaxy supports the interpretation of damped Lyα clouds as objects fundamentally different from the lower column density Lyα forest clouds, which show weak or no clustering. The absorption trough itself shows no Lya emission, extended or unresolved, in either the Fabry-Perot frames or in deep, moderate resolution (∼3 Å FWHM), two-dimensional spectra, down to a limiting flux (3 σ) for an unresolved line of 2 ×10-17 ergs s-1 cm-2, ∼30 times fainter than the Lyα flux detected from the companion galaxy. The lack of strong Lya emission from the absorbing cloud can be interpreted as evidence either for a low SFR or for heavy dust obscuration

Fabry-Perot Images of NGC 1275 and Its Puzzling High-Velocity System

We report the first images obtained with the Goddard Fabry-Perot imager, a very sensitive and tunable imaging system designed to achieve the high levels of performance required in the optical studies of faint emission-line extragalactic objects. A velocity sequence of calibrated narrow-band CCD images (FWHM ∼7 Å) has been obtained to cover the 3000 km s-1 velocity space between the redshifted Hα emission lines of NGC 1275 (the central dominant galaxy of the Perseus Cluster), its extended associated system of low-velocity (LV) filaments and the high-velocity (HV) system of knots, projected on the same line of sight in the sky. The lack of intermediate-velocity emission-line gas between the two systems leads to an upper limit of 1.5 x 10-16 ergs cm-2 s-1 arcsec-2 (3 σ) on stripped ionized gas due to dynamical interaction between NGC 1275 and its high-velocity companion galaxy. It also confirms the previous reports that the level of continuum light arising from stellar or nonstellar sources must be very low in otherwise bright, strongly concentrated emission-line knots with unresolved diameters of 425 h-1 pc. The two galaxies are well separated kinematically. We have measured the Hα luminosities of the emission-line regions of the two systems and have derived star formation rates in order to investigate quantitatively the physical relation between the HV galaxy, NGC 1275, and the surrounding cooling flow filaments. We found that the 3′ diameter region around NGC 1275 has a total observed Hα luminosity of 5 x 1041 h-2 ergs s-1, a factor of 2.5 lower than a currently popular value (based on 1983 data). On the other hand, our measurements of central regions match other published values. Implications of this new measurement are discussed in the context of cooling flows. Corrected for Galactic foreground absorption, the Hα luminosity of NGC 1275 of LG(Hα) ∼ 1.2 x 1042 h-2 ergs s-1 is comparable to those of other strong cooling flows. A normal initial mass function (IMF) for star formation in NGC 1275 is consistent with published X-ray, UV, and optical data in this paper. In particular, the revised Hα luminosity of a strong emission-line extranuclear region can be reconciled with the limit on its continuum UV flux at 1250 Å; therefore, the exclusion of stars more massive than 25 M⊙ is no longer needed. Also, the hypothesis of a low-mass cutoff to the IMF at 2 M⊙, which had been introduced to reconcile the star formation rate (SFR) derived from the Hα luminosity with the mass deposition rate of X-ray gas (ṀX), is not needed when the revised value SFR ∼ 10 h-2 M⊙ yr-1 is compared with the similar value MX ∼ 7.5-15 h-2 M⊙ yr-1 within the 30″ radius central region. In the HV galaxy, the Ha luminosities of 13 regions have been measured in six narrow-band images, leading to a total observed luminosity L(Hα) = 7.2 x 1040 h-2 ergs s-1 over a surface area of 877 arcsec2. The star formation rate SFR ∼ 1 h-2 Ṁ yr-1 corresponds to a total stellar mass of 12 x 106 h-2 Ṁ if massive stars ionize the Hα knots. The collision of gas clouds in a heterogeneous intracluster medium with the fast-moving HV galaxy has been modeled. Following the collision, the HV interstellar medium becomes violently perturbed, with giant expanding cavities sweeping considerable masses of gas. Star formation with a 2-4 h-2 % efficiency in the HV shocked disk supershells may occur under favorable conditions 1-8 Myr after the collision event