Constraints on the Lyman continuum radiation from galaxies: first results with FUSE on Mrk 54

We present Far Ultraviolet Spectroscopic Explorer observations of the star-forming galaxy Mrk 54 at z = 0.0448. The Lyman continuum radiation is not detected above the HI absorption edge in our Galaxy. An upper limit is evaluated by comparison with the background measured in regions of the detector adjacent to the observed spectrum. A spectral window of 16 A, reasonably free of additional HI Lyman series line absorption is used. No correction is needed for molecular hydrogen absorption in our Galaxy but a foreground extinction of 0.29 mag is accounted for. An upper limit of 6.15 10^{-16} erg/cm^2/s/A is obtained for the flux at ~ 900 A in the rest frame of Mrk 54. By comparison with the number of ionizing photons derived from the H-alpha flux, this limit translates into an upper limit of f_esc < 0.062 for the fraction of Lyman continuum photons that escape the galaxy without being absorbed by interstellar material. This limit compares with the limits obtained in three other nearby galaxies and is compatible with the escape fractions predicted by models. The upper limits obtained in nearby galaxies contrasts with the detection of Lyman continuum flux in the composite spectrum of Lyman-break galaxies at z ~ 3.4. The difficulties and implications of a comparison are discussed.Comment: 9 pages, 3 figures, accepted for publication in A&A include aa.cls v5.0

Surprisingly Little O VI Emission Arises in the Local Bubble

This paper reports the first study of the O VI resonance line emission (1032, 1038 Angstroms) originating in the Local Bubble (or Local Hot Bubble) surrounding the solar neighborhood. In spite of the fact that O VI absorption within the Local Bubble has been observed, no resonance line emission was detected during our 230 ksec Far Ultraviolet Spectroscopic Explorer observation toward a ``shadowing'' filament in the southern Galactic hemisphere. As a result, tight 2 sigma upper limits are set on the intensities in the 1032 and 1038 Angstrom emission lines: 500 and 530 photons cm^{-2} s^{-1} sr^{-1}, respectively. These values place strict constraints on models and simulations. They suggest that the O VI-bearing plasma and the X-ray emissive plasma reside in distinct regions of the Local Bubble and are not mixed in a single plasma, whether in equilibrium with T ~ 10^6 K or highly overionized with T ~ 4 to 6 x 10^4 K. If the line of sight intersects multiple cool clouds within the Local Bubble, then the results also suggest that hot/cool transition zones differ from those in current simulations. With these intensity upper limits, we establish limits on the electron density, thermal pressure, pathlength, and cooling timescale of the O VI-bearing plasma in the Local Bubble. Furthermore, the intensity of O VI resonance line doublet photons originating in the Galactic thick disk and halo is determined (3500 to 4300 photons cm^{-2} s^{-1} sr^{-1}), and the electron density, thermal pressure, pathlength, and cooling timescale of its O VI-bearing plasma are calculated. The pressure in the Galactic halo's O VI-bearing plasma (3100 to 3800 K cm^{-3}) agrees with model predictions for the total pressure in the thick disk/lower halo. We also report the results of searches for other emission lines.Comment: accepted by ApJ, scheduled for May 2003, replacement astro-ph submission corrects typos and grammatical errors in original versio

Herschel observations of interstellar chloronium. II - Detections toward G29.96-0.02, W49N, W51, and W3(OH), and determinations of the ortho-to-para and 35^{35}Cl/37^{37}Cl isotopic ratios

We report additional detections of the chloronium molecular ion, H$_2$Cl$^+$, toward four bright submillimeter continuum sources: G29.96, W49N, W51, and W3(OH). With the use of the HIFI instrument on the Herschel Space Observatory, we observed the $2_{12}-1_{01}$ transition of ortho-H$_2^{35}$Cl$^+$ at 781.627 GHz in absorption toward all four sources. Much of the detected absorption arises in diffuse foreground clouds that are unassociated with the background continuum sources and in which our best estimates of the $N({\rm H_2Cl^+})/N({\rm H})$ ratio lie in the range $(0.9 - 4.8) \times 10^{-9}$. These chloronium abundances relative to atomic hydrogen can exceed the predictions of current astrochemical models by up to a factor of 5. Toward W49N, we have also detected the $2_{12}-1_{01}$ transition of ortho-H$_2^{37}$Cl$^+$ at 780.053 GHz and the $1_{11}-0_{00}$ transition of para-H$_2^{35}$Cl$^+$ at 485.418 GHz. These observations imply $\rm H_2^{35}Cl^+/H_2^{37}Cl^+$ column density ratios that are consistent with the solar system $^{35}$Cl/$^{37}$Cl isotopic ratio of 3.1, and chloronium ortho-to-para ratios consistent with 3, the ratio of spin statistical weights.Comment: 31 pages, including 7 figures. Accepted for publication in the Ap

Microstructure of the Local Interstellar Cloud and the Identification of the Hyades Cloud

We analyze high-resolution UV spectra of the Mg II h and k lines for 18 members of the Hyades Cluster to study inhomogeneity along these proximate lines of sight. The observations were taken by the Space Telescope Imaging Spectrograph (STIS) instrument on board the Hubble Space Telescope (HST). Three distinct velocity components are observed. All 18 lines of sight show absorption by the Local Interstellar Cloud (LIC), ten stars show absorption by an additional cloud, which we name the Hyades Cloud, and one star exhibits a third absorption component. The LIC absorption is observed at a lower radial velocity than predicted by the LIC velocity vector derived by Lallement & Bertin (1992) and Lallement et al. (1995), (v(predicted LIC) - v(observed LIC) = 2.9 +/- 0.7 km/s), which may indicate a compression or deceleration at the leading edge of the LIC. We propose an extention of the Hyades Cloud boundary based on previous HST observations of other stars in the general vicinity of the Hyades, as well as ground-based Ca II observations. We present our fits of the interstellar parameters for each absorption component. The availability of 18 similar lines of sight provides an excellent opportunity to study the inhomogeneity of the warm, partially ionized local interstellar medium (LISM). We find that these structures are roughly homogeneous. The measured Mg II column densities do not vary by more than a factor of 2 for angular separations of < 8 degrees, which at the outer edge of the LIC correspond to physical separations of < 0.6 pc.Comment: 35 pages, 11 figures, AASTEX v.5.0 plus EPSF extensions in mkfig.sty; accepted by Ap

Studying the Pulsation of Mira Variables in the Ultraviolet

We present results from an empirical study of the Mg II h & k emission lines of selected Mira variable stars, using spectra from the International Ultraviolet Explorer (IUE). The stars all exhibit similar Mg II behavior during the course of their pulsation cycles. The Mg II flux always peaks after optical maximum near pulsation phase 0.2-0.5, although the Mg II flux can vary greatly from one cycle to the next. The lines are highly blueshifted, with the magnitude of the blueshift decreasing with phase. The widths of the Mg II lines are also phase-dependent, decreasing from about 70 km/s to 40 km/s between phase 0.2 and 0.6. We also study other UV emission lines apparent in the IUE spectra, most of them Fe II lines. These lines are much narrower and not nearly as blueshifted as the Mg II lines. They exhibit the same phase-dependent flux behavior as Mg II, but they do not show similar velocity or width variations.Comment: 26 pages, 12 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty; to appear in Ap

The Ionization of the Local Interstellar Medium, as Revealed by FUSE Observations of N, O and Ar toward White Dwarf Stars

FUSE spectra of the white dwarf stars G191-B2B, GD 394, WD 2211-495 and WD 2331-475 cover the absorption features out of the ground electronic states of N I, N II, N III, O I and Ar I in the far ultraviolet, providing new insights on the origin of the partial ionization of the Local Interstellar Medium (LISM), and for the case of G191-B2B, the interstellar cloud that immediately surrounds the solar system. Toward these targets the interstellar abundances of Ar I, and sometimes N I, are significantly below their cosmic abundances relative to H I. In the diffuse interstellar medium, these elements are not likely to be depleted onto dust grains. Generally, we expect that Ar should be more strongly ionized than H (and also O and N whose ionizations are coupled to that of H via charge exchange reactions) because the cross section for the photoionization of Ar I is very high. Our finding that Ar I/H I is low may help to explain the surprisingly high ionization of He in the LISM found by other investigators. Our result favors the interpretation that the ionization of the local medium is maintained by a strong EUV flux from nearby stars and hot gases, rather than an incomplete recovery from a past, more highly ionized condition.Comment: 13 pages, 2 figures. To appear in a special issue of the Astrophysical Journal Letters devoted to the first scientific results from the FUSE missio

Deuterium toward the WD0621-376 sight line: Results from the Far Ultraviolet Spectroscopic Explorer (FUSE) Mission

Far Ultraviolet Spectroscopic Explorer observations are presented for WD0621-376, a DA white dwarf star in the local interstellar medium (LISM) at a distance of about 78 pc. The data have a signal-to-noise ratio of about 20-40 per 20 km/s resolution element and cover the wavelength range 905-1187 \AA. LISM absorption is detected in the lines of D I, C II, C II*, C III, N I, N II, N III, O I, Ar I, and Fe II. This sight line is partially ionized, with an ionized nitrogen fraction of > 0.23. We determine the ratio $D/O = (3.9 \pm ^{1.3}_{1.0})\times 10^{-2}$ (2$\sigma$). Assuming a standard interstellar oxygen abundance, we derive ${\rm D/H} \approx 1. 3 \times 10^{-5}$. Using the value of N(H I) derived from EUVE data gives a similar D/H ratio. The D I/N I ratio is $(3.3 \pm ^{1.0}_{0.8})\times 10^{-1}$ (2$\sigma$).Comment: accepted for publication in the ApJ

Clinical proteomics of myeloid leukemia

Myeloid leukemias are a heterogeneous group of diseases originating from bone marrow myeloid progenitor cells. Patients with myeloid leukemias can achieve long-term survival through targeted therapy, cure after intensive chemotherapy or short-term survival because of highly chemoresistant disease. Therefore, despite the development of advanced molecular diagnostics, there is an unmet need for efficient therapy that reflects the advanced diagnostics. Although the molecular design of therapeutic agents is aimed at interacting with specific proteins identified through molecular diagnostics, the majority of therapeutic agents act on multiple protein targets. Ongoing studies on the leukemic cell proteome will probably identify a large number of new biomarkers, and the prediction of response to therapy through these markers is an interesting avenue for future personalized medicine. Mass spectrometric protein detection is a fundamental technique in clinical proteomics, and selected tools are presented, including stable isotope labeling with amino acids in cell culture (SILAC), isobaric tags for relative and absolute quantification (iTRAQ) and multiple reaction monitoring (MRM), as well as single cell determination. We suggest that protein analysis will play not only a supplementary, but also a prominent role in future molecular diagnostics, and we outline how accurate knowledge of the molecular therapeutic targets can be used to monitor therapy response

Dust in the Ionized Medium of the Galaxy: GHRS Measurements of Al III and S III

We present interstellar absorption line measurements of the ions S III and Al III towards six stars using archival Goddard High Resolution Spectrograph data. The ions Al III and S III trace heavily depleted and non-depleted elements, respectively, in ionized gas. We use the photoionization code CLOUDY to derive the ionization correction relating N(Al III)/N(S III) to the gas-phase abundance [Al/S]_i in the ionized gas. For spectral types considered here, the corrections are small and independent of the assumed ionization parameter. Using the results of these photoionization models, we find [Al/S]_i = -1.0 in the ionized gas towards three disk stars. These values of [Al/S]_i (=[Al/H]_i) imply that Al-bearing grains are present in the ionized nebulae around these stars. If the WIM of the Galaxy is photoionized by OB stars, our data for two halo stars imply [Al/S]_i = -0.4 to -0.5 in the WIM and thus the presence of dust grains containing Al in this important phase of the ISM. While photoionization appears to be the most likely origin of the ionization for Al III and S III, we cannot rule out confusion from the presence of hot, collisionally ionized gas along two sightlines. We find that [Al/S]_i in the ionized gas along the six sightlines is anti-correlated with the electron density and average sightline neutral density. The degree of grain destruction in the ionized medium of the Galaxy is not much higher than in the warm neutral medium. The existence of grains in the ionized regions studied here has important implications for the thermal balance of these regions. (Abstract Abridged)Comment: 30 pages including 8 embedded tables and 8 embedded figures. Accepted for publication in the Astrophysical Journa

IMAPS Observations of Interstellar Neutral Argon and the Implications for Partially Ionized Gas

We use the absorption features from neutral argon at 1048 and 1066 A to determine interstellar abundances or their lower limits toward nine early-type stars. These features were observed with the Interstellar Medium Absorption Profile Spectrograph (IMAPS) along sight lines with low reddening and low fractional abundances of molecular hydrogen. We find that the interstellar Ar I is below its solar and B-star abundance with respect to hydrogen toward zeta Pup, gamma2 Vel and beta Cen A with (logarithmic) reduction factors -0.37+/-0.09, -0.18+/-0.10, and -0.61+/-0.12 dex, respectively. While Ar can condense onto the surfaces of dust grains in the interiors of dense clouds, it is unlikely that argon atoms are depleted by this process in the low-density lines of sight considered in this study. Instead, we propose that the relatively large photoionization cross section of Ar makes it much easier to hide in its ionized form than H. In regions that are about half ionized, this effect can lower Ar I/H I by -0.11 to -0.96 dex, depending on the energy of the photoionizing radiation and its intensity divided by the local electron density. We apply this interpretation for the condition of the gas in front of beta Cen A, which shows the largest deficiency of Ar. Also, we determine the expected magnitudes of the differential ionizations for He, N, O, Ne and Ar in the partly ionized, warm gas in the local cloud around our solar system. For the local cloud and others that can be probed by UV studies, the observed Ar I to H I ratio may be a good discriminant between two possible alternatives, collisional ionization or photoionization, for explaining the existence of partly ionized regions.Comment: 36 pages, 3 figure