UV Counterparts Research Articles

Discovery of Faint Ultraviolet Sources in the Globular Cluster NGC 6624 with the [ITAL]Hubble Space Telescope[/ITAL

Using the Faint Object Camera (FOC) on the Hubble Space Telescope (HST), we have identified three faint ultraviolet sources in the innermost ~15 arcseconds of the globular cluster NGC 6624. These sources are in addition to the previously discovered UV counterpart to the X-ray source 4U 1820-30, which is observed in the same field. At 1400 A, the sources have dereddened fluxes of 4.4 × 10-16 to 1.8 × 10-15 erg cm-2 s-1 A-1. The faintest source is within the field of view of an existing HST/FOC B image; its B magnitude is ~23.4, or MB ~ 7.8. The two fainter sources may be hot white dwarfs, although it would be unusual to observe two of these objects at such a young age. Alternatively, one or more of the sources could be hot, helium-burning subdwarfs. In particular, the brightest source may be on the extreme blue end of the horizontal branch, which would be notable, as NGC 6624 is a metal-rich cluster with a red horizontal branch. Finally, one or more of these stars could be cataclysmic variables. We briefly discuss future observations that could distinguish among these possibilities.

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

view Abstract Citations (44) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of an Ultraviolet and Visible Counterpart of the NGC 6624 X-Ray Burster King, I. R. ; Stanford, S. A. ; Albrecht, R. ; Barbieri, C. ; Blades, J. C. ; Boksenberg, A. ; Crane, P. ; Disney, M. J. ; Deharveng, J. M. ; Jakobsen, P. ; Kamperman, T. M. ; Macchetto, F. ; Mackay, C. D. ; Paresce, F. ; Weigelt, G. ; Baxter, D. ; Greenfield, P. ; Jedrzejewski, R. ; Nota, A. ; Sparks, W. B. ; Sosin, C. Abstract We have detected, in images taken with the HST FOC, the UV and optical counterpart of the X-ray source 4U 1820-30 in the globular cluster NGC 6624. Astrometric measurements place this object 2 sigma from the X-ray position of 4U 1820-30. The source dominates a far-UV FOC image and has the same flux at 1400 A as was seen through the large IUE aperture by Rich et al. (1993). It has a B magnitude of 18.7 but is not detected in V. It is 0.66 arcsec from the center of NGC 6624, a fact that may change the interpretation of the P-average of the 11 minute binary orbit. The flux drops between 1400 and 4300 A at a rate that is nearly as steep as that of a Rayleigh-Jeans curve. The flux is far too large to come from the neutron star directly but could accord with radiation from a heated accretion disk and/or the heated side of the companion star. Publication: The Astrophysical Journal Pub Date: August 1993 DOI: 10.1086/186973 Bibcode: 1993ApJ...413L.117K Keywords: Globular Clusters; Iue; Ultraviolet Astronomy; X Ray Sources; Astrometry; Neutron Stars; Visible Spectrum; Astrophysics full text sources ADS | data products SIMBAD (2) MAST (2) ESA (1)

Response to color by male and female Frankliniella occidentalis during swarming and non‐swarming behavior

AbstractResponses of male and female Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) to colors of various hues and brightness levels were compared between swarming and non‐swarming behavior periods. Relative rankings of color preference were similar between males and females and between swarming and non‐swarming behavior periods. Numbers of thrips were higher on blues, violets, white and somewhat less on some yellows, while lower numbers were found on greens, reds, some yellows and highly UV reflective white. The effect of UV reflection on thrips response to color depended upon the amount of UV reflectance. Highly UV reflective white (78% reflectance at 365 nm) captured very few thrips compared with low UV white (14% reflectance at 365 nm), but colors with less than 35% UV reflectance had no negative effect on numbers of thrips captured compared with their lower UV counterparts. Correlations of average preference rank of colors across all tests with relative rank of brightness of the colors (based on the area under the reflectance curve in different spectral ranges) indicated highly significant correlations of preference with the brightness in the blue‐violet range (R = 0.69 for females; R = 0.86 for males, P < 0.0021), but no significant correlation with brightness in the visible, green‐yellow, or UV range. This contrasts with previous physiological research which indicates that spectral response efficiency of this species peaks in the UV and at 540 nm (green‐yellow range). Several possible physiological, behavioral and color brightness explanations for this discrepancy are discussed.Significantly higher numbers of male thrips were trapped during swarming (4.5–6.3 ×) compared with non‐swarming behavior periods. Significantly higher numbers of males were trapped than females during swarming behavior periods, but more females were trapped than males during non‐swarming behavior periods. Sex ratios during non‐swarming periods approximated sex ratios found in populations in plants. Based on the density change relative to sex ratio change between behavior periods, there was an indication of a greater change in male behavior than in female behavior. Since males and females responded similarly to color during both behavior periods and attractive colors were similar to flower colors, this suggests that male thrips use resource‐based areas for aggregation sites.

Liquid chromatography—thermospray mass spectrometric study of N-acylamino dilactones and 4-butyrolactones derived from antimycin A

Reversed-phase high-performance liquid chromatography—thermospray mass spectrometric (HPLC—MS) characteristics of four sets of lactonic complexes (one 4-butyrolactones and three dilactone complexes) derived from antimycin A were investigated. Three types of 8-hydroxy analogues were also included in the study. Pairs of a–b structures isomeric at the 8-acyloxy ester side-chains were best separated with a high-efficiency octadecylsilica column prior to analysis by HPLC—MS. Mass spectra of the a–b pairs each with identical molecular weights exhibited virtually indistinguishable fragmentation patterns, although their relative intensities were not superimposable. In some cases, HPLC—MS of the title compounds yielded mass chromatograms showing the minor components more easily recognizable than the HPLC—UV counter parts because of the apparent higher ionization efficiency of the minor isomers and increased resolution of subcomponents in the MS system. Under the mobile phase conditions employed, analyte ionization occurred with variable degrees of gas phase ammonolysis depending upon the ammonia concentration of the buffer. Potential applicability of the on-line HPLC—MS technique for the characterization of components in mixtures of antimycin analogues and isomers is demonstrated.

Images in the rocket ultraviolet - Star formation and extinction in the M51 system

UV images of M51 with up to 15" resolution were obtained by a rocket- borne telescope. The bandwidth was 970 A with maximum response at 2650 A. The two most prominent features of M51 in the UV are the bright central region and a region of intense star formation about 2.5' NE of the nucleus toward the companion NGC 5195. This complex is the source of 20% of the total UV flux in M51. The companion is much less prominent in the UV than in optical bands. Spiral arms show much higher contrast in UV and U bands than in the R band. The nuclear region in the UV band shows clumped emission from probable star-forming regions, possibly associated with the inner Lindblad resonance. These regions are probably the UV counterparts of FIR sources discovered in an EW scan across the nucleus. UV/U colors of most bright H II regions with known extinction are consistent with O star spectra reddened by amounts estimated from radio and Balmer line measurements. However, some of the brightest H II regions have redder UV/U colors, probably indicating the presence of cooler stars which contribute in the U band. CO and IR observations indicate that the companion NGC 5195 may be a reddened starburst in spite of its faintness in the UV.