Near-IR [Fe ii] Emission Diagnostics: Disk Winds in Young Stars

We investigate in this contribution emissivity properties of the [Fe ii] near-IR lines and their application to the study of jets in young stars. We report a model-independent method to determine the gas phase abundance in jets. Then, we present synthetic maps deduced from a recent self-consistent MHD cold disk wind model from which the thermal solution has been solved a posteriori. Kinematics is compared with observations in the [Fe ii] near-IR lines of L1551-IRS5. General kinematical behaviour is well reproduced, the existence of two velocity components in particular. However, we note a relative deficit in emission at intermediate velocity as observed in the jets from optically visible T Tauri stars. We examine predicted rotation signatures for various types of MHD disk winds. Compared to observations of DG Tau, warm disk winds reproduce quite well observed velocity shifts, whereas cold solutions predict too high toroidal velocities by a factor 2–3.     

The G‐dwarf problem in the solar neighbourhood: II. Halo subdwarfs

The oxygen abundance distribution in solar neighbourhood halo subdwarfs is deduced, using two alternative, known empirical relationships, involving the presence or the absence of [O/Fe] plateau for low [Fe/H] values, from a sample of 372 kinematically selected halo stars, for which the iron abundance distribution has been determined by Ryan & Norris (1991). The data are interpreted by a simple, either homogeneous or inhomogeneous model of chemical evolution, using an updated value of the solar oxygen abundance. The effect of changing the solar oxygen abundance, the power‐law exponent in the initial mass function, and the rate of oxygen nucleosyntesis, keeping the remaining input parameters unchanged, is investigated, and a theorem is stated. In all cases, part of the gas must necessarily be inhibited from forming stars, and no disk contamination has to be advocated for fitting the empirical oxygen abundance distribution in halo subdwarfs of the solar neighbourhood (EGD). Then a theorem is stated, which allows a one‐to‐one correspondence between simple, homogeneous models with and without inhibited gas, related to same independent parameters of chemical evolution, except lower stellar mass limit, real yield, and inhibition parameter. The mutual correlations between the latter parameters are also specified. In addition the starting point, and the point related to the first step, of the theoretical distribution of oxygen abundance (TGD) predicted by simple, inhomogeneous models, is calculated analytically. The mean oxygen abundance of the total and only inhibited gas, respectively, are also determined. Following the idea of a universal, initial mass function (IMF), a power‐law with both an exponent p = 2.9, which is acceptably close to Scalo IMF for m ≳ m_⊙, and an exponent p = 2.35, i.e. Salpeter IMF, have been considered. In general, both the age‐metallicity relationship and the empirical distribution of oxygen abundance in G dwarfs of the disk solar neighbourhood, are fitted by power‐law IMF exponents in the range 2.35 ≤ p ≤ 2.9. Acceptable models predict about 15% of the total mass in form of long‐lived stars and remnants, at the end of halo evolution, with a mean gas oxygen abundance which is substantially lower than the mean bulge and initial disk oxygen abundance. To avoid this discrepancy, either the existence of a still undetected, baryonic dark halo with about 15% of the total mass, or an equal amount of gas loss during bulge and disk formation, is necessary. The latter alternative implies a lower stellar mass limit close to 0.2 m_⊙, which is related to a power‐law IMF exponent close to 2.77. Acceptable models also imply a rapid halo formation, mainly during the first step, Δt = 0.5 Gyr, followed by a period (three steps) where small changes occur. Accordingly, statistical fluctuations are found to produce only minor effects on the evolution.     

Oxygen abundance in local disk and bulge: chemical evolution with a strictly universal IMF

This paper has two parts: one about observational constraints related to the empirical differential oxygen abundance distribution (EDOD), and the other about inhomogeneous models of chemical evolution, in particular the theoretical differential oxygen abundance distribution (TDOD). In the first part, the EDOD is deduced from subsamples related to two different samples involving (i) N=532 solar neighbourhood (SN) stars within the range, −1.5<[Fe/H]<0.5, for which the oxygen abundance has been determined both in presence and in absence of the local thermodynamical equilibrium (LTE) approximation (Ramirez et al. in Astron. Astrophys. 465:271, 2007); and (ii) N=64 SN thick disk, SN thin disk, and bulge K-giant stars within the range, −1.7<[Fe/H]<0.5, for which the oxygen abundance has been determined (Melendez et al. in Astron. Astrophys. 484:L21, 2008). A comparison is made with previous results implying use of [O/H]–[Fe/H] empirical relations (Caimmi in Astron. Nachr. 322:241, 2001b; New Astron. 12:289, 2007) related to (iii) 372 SN halo subdwarfs (Ryan and Norris in Astron. J. 101:1865, 1991); and (iv) 268 K-giant bulge stars (Sadler et al. in Astron. J. 112:171, 1996). The EDOD of the SN thick + thin disk is determined by weighting the mass, for assumed SN thick to thin disk mass ratio within the range, 0.1–0.9. In the second part, inhomogeneous models of chemical evolution for the SN thick disk, the SN thin disk, the SN thick + thin disk, the SN halo, and the bulge, are computed assuming the instantaneous recycling approximation. The EDOD data are fitted, to an acceptable extent, by their TDOD counterparts with the exception of the thin or thick + thin disk, where two additional restrictions are needed: (i) still undetected, low-oxygen abundance thin disk stars exist, and (ii) a single oxygen overabundant star is removed from a thin disk subsample. In any case, the (assumed power-law) stellar initial mass function (IMF) is universal but gas can be inhibited from, or enhanced in, forming stars at different rates with respect to a selected reference case. Models involving a strictly universal IMF (i.e. gas neither inhibited from, nor enhanced in, forming stars with respect to a selected reference case) can also reproduce the data to an acceptable extent. Our main conclusions are (1) different models are necessary to fit the (incomplete) halo sample, which is consistent with the idea of two distinct halo components: an inner, flattened halo in slow prograde rotation, and an outer, spherical halo in net retrograde rotation (Carollo et al. in Nature 450:1020, 2007); (2) the oxygen enrichment within the inner SN halo, the SN thick disk, and the bulge, was similar and coeval within the same metallicity range, as inferred from observations (Prochaska et al. in Astron. J. 120:2513, 2000); (3) the fit to thin disk data implies an oxygen abundance range similar to its thick disk counterpart, with the extension of conclusion (2) to the thin disk, and the evolution of the thick + thin disk as a whole (Haywood in Mon. Not. R. Astron. Soc. 388:1175, 2008) cannot be excluded; (4) leaving outside the outer halo, a fit to the data related to different environments is provided by models with a strictly universal IMF but different probabilities of a region being active, which implies different global efficiencies of the star formation rate; (5) a special case of stellar migration across the disk can be described by models with enhanced star formation, where a fraction of currently observed SN stars were born in situ and a comparable fraction is due to the net effect of stellar migration, according to recent results based on high-resolution N-body + smooth particle hydrodynamics simulations (Roškar et al. in Astrophys. J. Lett. 684:L79, 2008).     

Abundance Ratios in Metal-Rich Halo and Thick-Disk Stars

Recent determinations of precise abundance ratios for nearby halo and thick disk stars in the metallicity range −1.3 < [Fe/H] < −0.5 have revealed a significant cosmic spread in the abundances of oxygen, magnesium, sodium, nickel, s-process and r-process elements relative to iron. Possible explanations of these variations are reviewed. In particular, it is discussed if the differences in abundance ratios are correlated with the kinematics of the stars, and hence can be used to identify stellar populations in the Galaxy. This revised version was published online in July 2006 with corrections to the Cover Date.     

The forbidden line [Ca ii] λ7323 in the fraunhofer spectrum

New observations of the [Caii] 7323 Fraunhofer line are reported. The blending H₂O line was weak at the time of observation. Accurate estimates of the centre-limb variation of the equivalent width of the [Caii] transition are obtained and shown to be consistent with the calcium abundance log N(Ca) = 6.33.     

Mg/Fe Ratios in Hierarchically-Forming Ellipticals

In the framework of semi-analytic models for hierarchical galaxy formation, star formation in ellipticals is not truncated but continues to low redshift. I show that, because of this extended star formation history, such models fail to reproduce super-solar Mg/Fe ratios in the global stellar populations. The abundance ratios in the starburst population that forms in the major merger are analysed. It turns out that a considerable flattening of the initial mass function with respect to the Salpeter slope is required in order to achieve overabundant Mg/Fe ratios. The resulting metallicities of the burst population exceed the observed values unless the efficiency of burst star formation is substantially lowered. The abundance features of the global–burst mixture for different proportions and varying IMF slope are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radial velocities andDDO, BV photometry of Henry Draper G5-M stars near the North Galactic Pole

Radial velocities are given for some 900 stars within 15‡ of the North Galactic Pole, including almost all such stars classified G5 or later in theHenry Draper Catalogue. Luminosities, two-dimensional spectral classes, composition indices, and distances are derived for the majority of the sample throughDDO andBV photometry. More than half of the stars are classified as G5-K5 giants: they show a clear relationship between composition and velocity dispersion for the two Galactic componentsV andW, and a less well-defined trend forU. Four abundance groups exhibit characteristics which imply association with, respectively, the thick disk, old thin disk, young thin disk, and Roman’s “4150” group. The sample is contained within l kpc of the Galactic plane, and no trends with distance are evident.     

Abundances of [WC] central stars and their planetary nebulaee

We review elemental abundances derived for planetary nebula (PN) WCcentral stars and for their nebulae. Uncertainties in the abundances of[WC] stars are still too large to enable an abundance sequenceto be constructed. In particular it is not clear why the hotter [WCE]stars have C and O abundances which are systematically lower than those oftheir supposed precursors, the [WCL] stars. This abundance differencecould be real or it may be due to unaccounted-for systematic effects inthe analyses. Hydrogen might not be present in [WC] star winds asoriginallysuggested, since broad pedestals observed at the base of nebular lines canplausibly be attributed to high velocity nebular components. It isrecommended that stellar abundance analyses should be carried out withnon-LTE model codes, although recombination line analyses can provideuseful insights. In particular, C II dielectronic recombinationlines provide a unique means to determine electron temperatures in cool[WC] star winds. We then compare the abundances found for PNe which have [WC] central starswith those that do not. Numerous abundance analyses of PNe have beenpublished, but comparisons based on non-uniform samples and methods arelikely to lack reliability. Nebular C/H ratios, which might be expected todistinguish between PNe around H-poor and H-rich stars, are rather similarfor the two groups, with only a small tendency towards larger values fornebulae around H-deficient stars. Nebular abundances should be obtainedwith photoionization models using the best-fitting non-LTE modelatmosphere for the central star as the input. Heavy-metal line blanketingstill needs to be taken into consideration when modeling the central star,as its omission can significantly affect the ionizing fluxes as well asthe abundance determinations. We discuss the discrepancies between nebularabundances derived from collisionally excited lines and thosederived from optical recombination lines, a phenomenon that may havelinks with the presence of H-deficient central stars.     

Helium contamination from the progenitor stars of planetary nebulae: The He/H radial gradient and the ΔY / ΔZ enrichment ratio

In this work, two aspects of the chemical evolution of ⁴He in the Galaxy are considered on the basis of a sample of disk planetary nebulae (PN). First, an application of corrections owing to the contamination of ⁴He from the evolution of the progenitor stars shows that the He/H abundance by number of atoms is reduced by 0.012 to 0.015 in average, leading to an essentially flat He/H radial distribution. Second, a determination of the helium to heavy element enrichment ratio using the same corrections leads to values in the range 2.8 < ΔY / ΔZ < 3.6 for Y _p = 0.23 and 2.0 < ΔY / ΔZ < 2.8 for Y _p = 0.24, in good agreement with recent independent determinations and theoretical models. This revised version was published online in July 2006 with corrections to the Cover Date.     

慧眼-HXMT观测到的黑洞双星系统中的W-K 关系

通过几十年的观测研究, 黑洞X射线双星(X-Ray Binary, XRB)部分特征被揭示. 然而, 吸积盘结构尚不确定. 黑洞XRB功率密度谱的截断频率与准周期振荡(Quasi Periodic Oscillation, QPO)的相关性质(W-K关系)可以限制吸积盘结构. 利用慧眼-HXMT (Hard X-ray Modulation Telescope)观测到的5个黑洞XRB的数据, 对黑洞XRB的W-K关系进行了研究, 结果表明在慧眼-HXMT观测的3个探测器能段中W-K关系成立. 此外在MAXI J1535-571之中存在截断频率和吸积盘内半径的相关关系, 这和截断的吸积盘结构一致. 如果观测到的功率密度谱来自质量吸积率的扰动传播, 可以推测吸积盘内半径接近最内圆形稳定轨道, 此黑洞可能是高自旋系统.     

Si VII/Mg VII and Si IX/Mg IX line diagnostics for solar plasma

New calculations for Si vii/Mg vii and Si ix/Mg ix theoretical line ratios as a tool for plasma density diagnostics and for the estimation of relative element abundance in the solar atmosphere are presented, making use of the EUV spectrum of an active region obtained by the Solar EUV Rocket Telescope and Spectrograph (SERTS). Theoretical line ratios, hitherto not observed, are discussed for diagnosing solar plasma from the observations obtainable with the Coronal Diagnostic Spectrometer (CDS) instrument on board the SOHO mission.In the honour of Dr P. K. Raju, Indian Institute of Astrophysics, Bangalore, on the completion of his 60 years.     

A galactic model with a pulsating active nucleus

The chemical evolution of the Galaxy with a pulsating active nucleus is investigated. The surface densities of gas, stellar remnants, stars and chemical species such as helium and heavy elements inZ6 are calculated as functions of the position in the Galaxy and of the evolutional time of the Galaxy. According to this model, the entire luminosity of the galactic disk becomes almost constant at some 2×10⁹ yr after the galactic formation, but the nuclear bulge, whose dimensions gradually diminishes, becomes more and more luminous with time. On the other hand, the abundance depletion of helium and heavy elements appears in the inner region of the disk after some 6×10⁹ yr of the galactic formation. It also becomes clear that the activity for the nucleosynthesis in the nucleus is limited only in the early history of the Galaxy and has been reduced rapidly with time. Using this model, we can account for the observed phenomena such as the smooth dependence of the elemental abundance in the halo population on the distance from the galactic center, the high abundance of heavy elements in quasar spectra and etc.     

Abundance Gradients as a tool for understanding the Formation of the Milky Way

According to the two-infall model for the chemical evolution of the Galaxy the halo and bulge formed on a relatively short timescale (0.8–1.0 Gyr) out of the first infall episode, whereas the disk accumulated much more slowly and ‘inside-out’ during a second independent infall episode. We explored the effects of a threshold in the star formation process, during both the halo and disk phases. In the comparison between model predictions and available data, we have focused our attention on abundance gradients as well as gas, stellar and star formation rate distributions along the disk. We suggest that the mechanism for the formation of the halo leaves detectable imprints on the chemical properties of the outer regions of the disk, whereas the evolution of the halo and the inner disk are almost completely disentangled. This is due to the fact that the halo and disk densities are comparable at large Galactocentric distances and therefore the gas lost from the halo can substantially contribute to building up the outer disk. We predict that the abundance gradients along the Galactic disk have increased in time during the first billion years of the disk evolution and remained almost constant in the last ~5Gyrs. This revised version was published online in September 2006 with corrections to the Cover Date.     

The oxygen abundance in the H II regions of the spiral galaxy M101 determined from the Sloan Digital Sky Survey spectra

We examined the Sloan Digital Sky Survey (SDSS) spectra of the H II regions in the disk of the spiral galaxy M101 (NGC 5457), and 17 H II regions with the auroral oxygen line [O III] λ 436.3 nm in their spectra were selected for line intensity measurements. The measurement data were used to determine the oxygen abundance in the H II region sample. We demonstrate that the spectral SDSS data supplemented with the information on the nebular oxygen line [O II] λ 372.7 nm based on the recently found ff-relation between the oxygen line intensities in the spectra of H II regions allow the oxygen abundance to be determined as accurately as in the standard T _e method. The parameters of the radial oxygen abundance distribution in the M101 disk (the abundance at the galactic center and the radial gradient) are estimated.     

[WR] nuclei of planetary nebulae: Inferences from statistical studies of the nebulae

There are about 50 galactic planetary nebulae know to have [WR] type nuclei. We have compared their nebular properties with those of the other planetary nebulae in the Galaxy. We have found that the nebular morphological types are similarly distributed in the two groups. Bipolar nebulae constitute only 20% of the total in each group. The distribution of the nebular electron densities and abundance ratios N/O, He/H and C/O are the same in the two groups. The only marked difference is that nebular expansion velocities are larger in the group of planetary nebulae with [WR] central stars. We argue that the WR phenomenon does not preferentially occur in more massive central stars of planetary nebulae, contrary to what has been suggested in some former studies. We demonstrate that, for most of the observed [WR] type objects, the WR phenomenon cannot be triggered by a late helium shell flash event.The results of our investigation are published inAstronomy & Astrophysics 303, 893 (1995) and in the proceedings of the 2nd International Colloquium on Hydrogen-deficient Stars, C.S. Jeffery & U. Heber (eds), Astronomical Society of the Pacific Conference Series, Vol. 96, p. 209 (1996).     

Galactic scale gas flows in colliding galaxies: 3-Dimensional,N-body/hydrodynamics experiments

We present some results from three dimensional computer simulations of collisions between models of equal mass galaxies, one of which is a rotating, disk galaxy containing both gas and stars and the other is an elliptical containing stars only. We use fully self consistent models in which the halo mass is 2.5 times that of the disk. In the experiments we have varied the impact parameter between zero (head on) and 0.9R (whereR is the radius of the disk), for impacts perpendicular to the disk plane. The calculations were performed on a Cray 2 computer using a combined N-body/SPH program. The results show the development of complicated flows and shock structures in the direction perpendicular to the plane of the disk and the propagation outwards of a density wave in both the stars and the gas. The collisional nature of the gas results in a sharper ring than obtained for the star particles, and the development of high volume densities and shocks.     

The effect of increasing helium content and disk dwarfs evolution on the chemical enrichment of the Galaxy

This paper deals with two main effects: First the empirical metal abundance distribution in Main Sequence disk dwarfs of the solar neighbourhood, and second, the theoretical possibility of (i) an increased helium content as the Galaxy evolves, and (ii) the presence of evolutionary effects in disk dwarfs (i.e., the age of some or all stars considered up to the subgiant phase is not necessarily longer than the age of the galactic disk). We take into account a linear increase of helium content with metal content, and we impose some constraints relative to initial, solar and present-day observed values ofY andZ, and to observed relative helium to heavy element enrichment, Y/Z. In this way, little influence is found on the empirical metal abundance distribution in the range 0Y/Z3, while larger values of Y/Z would lead to a more significant influence. Evolved and unevolved theoretical metal abundance distributions are derived by accounting for a two-phase model of chemical evolution of galaxies and for a linear mass dependence of star lifetimes in the spectral range G2V–G8V, and are compared with the empirical distribution. All are in satisfactory agreement due to systematic shift data by different observations; several values o collapse timeT _c and age of the GalaxyT are also considered. Finally, models of chemical evolution invoking homogeneous collapse without infall and inhomogeneous collapse with infall, are briefly discussed relative to the empirical metal abundance distribution in Main Sequence disk dwarfs of the solar neighbourhood.     

The Mg/Ne abundance ratio in a recently emerged flux region observed by CDS

Evidence for the existence of the FIP-effect in the transition region is presented here based on recent observations from the Coronal Diagnostic Spectrometer (CDS) on-board the Solar and Heliospheric Observatory (SOHO). Observations of an emerging flux region in lines of Mgv–vii and Nevi–vii reveal differences in the relative Mg/Ne abundance of a factor of 9.2 between two transition region brightenings separated by less than 1 arc min on the Sun. The lower abundance ratio is approximately equal to the photospheric Mg/Ne value and is associated with a small loop-like feature in the central, hottest part of the active region. The higher abundance ratio is found in spike-like structures at the edge of the active region. A density diagnostic of Oiv is used to derive an electron number density of 10^11.3 cm^-3 for the low Mg/Ne brightening, while a Mgvii diagnostic gives a density of 10^9.2 cm for the high Mg/Ne brightening.     

Observations of Venus water vapor over the disk of Venus: The 1972–1974 data using the H2O lines at 8197 Å and 8176 Å

The Venus water vapor line at 8197.71 Å has been monitored at several positions on the disk of Venus and at phase angles between 21° and 162°. Variations in the abundance have been found with spatial location, phase angle and time. During the 1972–1974 period, the total two-way absorption has varied from less than 1 to 77 μm of water vapor. The dependence on phase angle indicates 20 to 50 μm over the disk between 30° and 110° and small, but detectable amounts present during the rest of the observations. The spatial distribution with respect to the intensity equator is uniform with no location on the disk having systematically a higher or lower abundance. Comparisons made between the water vapor abundandances and the CO₂ abundances determined from near-simultaneous observations of CO₂ bands at the same positions on the disk of Venus show no correlation for the majority of the samples.     

Empirical NLTE analyses of solar spectral lines

The center-to-limb behaviour of the Ba ii 4554 resonance line is analyzed together with data from the extreme limb, flash intensities and profiles of other Ba ii lines. An empirical NLTE method is employed in which the observed profiles are compared with synthesized profiles based on a standard one-dimensional model atmosphere, with the line source function, the barium abundance, the collisional damping and the atmospheric turbulence as free parameters.The line profiles from the extreme limb furnish considerable constraints on the formation of Ba ii 4554. Its wings reverse into emission well inside the solar limb, a phenomenon which cannot be explained by any frequency-independent line source function. Accounting for effects of partially coherent scattering in the line source function is a necessary and adequate step to reproduce the observations both over the disk and near the limb. The form of the empirically derived frequency-dependent line source function is discussed.Results are given for various parameters (gf-values, solar barium abundance and isotope ratios, collisional damping, microturbulence and macroturbulence).The 4554 profile of disk center shows a depression in its blue wing resembling asymetries found in various stellar spectral lines.