Sulfur Abundance Research Articles

SULFUR ABUNDANCES IN THE ORION ASSOCIATION B STARS

Sulfur abundances are derived for a sample of ten B main-sequence star members of the Orion association. The analysis is based on LTE plane-parallel model atmospheres and non-LTE line formation theory by means of a self-consistent spectrum synthesis analysis of lines from two ionization states of sulfur, SII and SIII. The observations are high-resolution spectra obtained with the ARCES spectrograph at the Apache Point Observatory. The abundance distribution obtained for the Orion targets is homogeneous within the expected errors in the analysis: A(S)=7.15+/-0.05. This average abundance result is in agreement with the recommended solar value (both from modelling of the photospheres in 1-D and 3-D, and meteorites) and indicates that little, if any, chemical evolution of sulfur has taken place in the last ~4.5 billion years. The sulfur abundances of the young stars in Orion are found to agree well with results for the Orion nebulae, and place strong constraints on the amount of sulfur depletion onto grains as being very modest or nonexistent. The sulfur abundances for Orion are consistent with other measurements at a similar galactocentric radius: combined with previous results for other OB-type stars produce a relatively shallow sulfur abundance gradient with a slope of -0.037+/-0.012 dex/kpc.

Elemental abundances and minimum mass of heavy elements in the envelope of HD 189733b

Oxygen (O) and carbon (C) have been inferred recently to be subsolar in abundance from spectra of the atmosphere of the transiting hot Jupiter HD 189733b. Yet, the mass and radius of the planet coupled with structure models indicate a strongly supersolar abundance of heavy elements in the interior of this object. Here we explore the discrepancy between the large amount of heavy elements suspected in the planet's interior and the paucity of volatiles measured in its atmosphere. We describe the formation sequence of the icy planetesimals formed beyond the snow line of the protoplanetary disk and calculate the composition of ices ultimately accreted in the envelope of HD 189733b on its migration pathway. This allows us to reproduce the observed volatile abundances by adjusting the mass of ices vaporized in the envelope. The predicted elemental mixing ratios should be 0.15--0.3 times solar in the envelope of HD 189733b if they are fitted to the recent O and C determinations. However, our fit to the minimum mass of heavy elements predicted by internal structure models gives elemental abundances that are 1.2--2.4 times oversolar in the envelope of HD189733b. We propose that the most likely cause of this discrepancy is irradiation from the central star leading to development of a radiative zone in the planet's outer envelope which would induce gravitational settling of elements. Hence, all strongly irradiated extrasolar planets should present subsolar abundances of volatiles. We finally predict that the abundances of nitrogen (N), sulfur (S) and phosphorus (P) are of $\sim$ $2.8 \times 10^{-5}$, $5.3 \times 10^{-6}$ and $1.8 \times 10^{-7}$ relative to H$_2$, respectively in the atmosphere of HD 189733b.

A VLT VIMOS integral-field spectroscopic study of perturbed blue compact galaxies: UM 420 and UM 462

We report on optical integral field spectroscopy of two unrelated blue compact galaxies mapped with the 13 x 13 arcsec^2 VIMOS integral field unit at a resolution of 0.33 x 0.33 arcsec^2. Continuum and background subtracted emission line maps in the light of [O III] 5007, H-alpha, and [N II] 6584 are presented. Both galaxies display signs of ongoing perturbation and/or interaction. UM 420 is resolved for the first time to be a merging system composed of two starbursting components with an 'arm-like' structure associated with the largest component. UM 462 which is a disrupted system of irregular morphology is resolved into at least four starbursting regions. Maps of the H-alpha radial velocity and FWHM are discussed. No underlying broad line region was detected from either galaxy as the emission lines are well-fitted with single Gaussian profiles only. Electron temperatures and densities as well as the abundances of helium, oxygen, nitrogen, and sulphur were computed from spectra integrated over the whole galaxies and for each area of recent star formation. Maps of the O/H ratio are presented: these galaxies show oxygen abundances that are ~20 per cent solar. No evidence of substantial abundance variations across the galaxies that would point to significant nitrogen or oxygen self-enrichment is found (<0.2 dex limit). Contrary to previous observations, this analysis does not support the classification of these BCGs as Wolf-Rayet galaxies as the characteristic broad emission line features have not been detected in our spectra. Baldwin-Phillips-Terlevich emission line ratio diagrams which were constructed on a pixel by pixel basis indicate that the optical spectra of these systems are predominantly excited by stellar photoionization.

A SPITZER HIGH-RESOLUTION MID-INFRARED SPECTRAL ATLAS OF STARBURST GALAXIES

We present an atlas of Spitzer/IRS high resolution (R~600) 10-37um spectra for 24 well known starburst galaxies. The spectra are dominated by fine-structure lines, molecular hydrogen lines, and emission bands of polycyclic aromatic hydrocarbons. Six out of the eight objects with a known AGN component show emission of the high excitation [NeV] line. This line is also seen in one other object (NGC4194) with, a priori, no known AGN component. In addition to strong polycyclic aromatic hydrocarbon emission features in this wavelength range (11.3, 12.7, 16.4um), the spectra reveal other weak hydrocarbon features at 10.6, 13.5, 14.2um, and a previously unreported emission feature at 10.75um. An unidentified absorption feature at 13.7um is detected in many of the starbursts. We use the fine-structure lines to derive the abundance of neon and sulfur for 14 objects where the HI 7-6 line is detected. We further use the molecular hydrogen lines to sample the properties of the warm molecular gas. Several basic diagrams characterizing the properties of the sample are also shown. We have combined the spectra of all the pure starburst objects to create a high S/N template, which is available to the community.

Sulfur Abundances in Orion B Stars

AbstractSulfur abundances are derived for a sample of ten B MS star members of the Orion association. The analysis is based on LTE model atmospheres and non-LTE line formation theory by means of spectrum synthesis analysis of Sii and Siii lines. The abundance distribution obtained for the Orion targets is homogeneous within the errors in the analysis: A(S)=7.15±0.05. This abundance result is in agreement with the solar value and with results for the Orion nebula. The sulfur abundances for Orion combined with previous results for other OB-type stars produce a relatively shallow sulfur abundance gradient with a slope of −0.037±0.012 dex Kpc−1.

UNUSUAL DUST EMISSION FROM PLANETARY NEBULAE IN THE MAGELLANIC CLOUDS

We present a Spitzer Space Telescope spectroscopic study of a sample of 25 planetary nebulae in the Magellanic Clouds. The low-resolution modules are used to analyze the dust features present in the infrared spectra. This study complements a previous work by the same authors where the same sample was analyzed in terms of neon and sulfur abundances. Over half of the objects (14) show emission of polycyclic aromatic hydrocarbons, typical of carbon-rich dust environments. We compare the hydrocarbon emission in our objects to those of Galactic HII regions and planetary nebulae, and LMC/SMC HII regions. Amorphous silicates are seen in just two objects, enforcing the now well-known-fact that oxygen-rich dust is less common at low metallicities. Besides these common features, some planetary nebulae show very unusual dust. Nine objects show a strong silicon carbide feature at 11um and twelve of them show magnesium sulfide emission starting at 25um. The high percentage of spectra with silicon carbide in the Magellanic Clouds is not common. Two objects show a broad band which may be attributed to hydrogenated amorphous carbon and weak low-excitation atomic lines. It is likely that these nebulae are very young. The spectra of the remaining eight nebulae are dominated by the emission of fine-structure lines with a weak continuum due to thermal emission of dust, although in a few cases the S/N in the spectra is low, and weak dust features may not have been detected.

Sulfur in the globular clusters 47 Tucanae and NGC 6752

The light elements Li, O, Na, Al, and Mg are known to show star to star variations in the globular clusters 47 Tuc and NGC 6752. Such variations are interpreted as due to processing in a previous generation of stars. In this paper we investigate the abundances of the alpha-element sulphur, for which no previous measurements exist. In fact this element has not been investigated in any Galactic globular cluster so far. The only globular cluster for which such measurements are available is Terzan 7, which belongs to the Sgr dSph. We use high resolution spectra of the S I Mult. 1, acquired with the UVES spectrograph at the 8.2m VLT-Kueyen telescope, for turn-off and giant stars in the two globular clusters. The spectra are analyzed making use of ATLAS static plane parallel model atmospheres and SYNTHE spectrum synthesis. We also compute 3D corrections from CO5BOLD hydrodynamic models and apply corrections due to NLTE effects taken from the literature. In the cluster NGC 6752 sulphur has been measured only in four subgiant stars. We find no significant star to star scatter and a mean <[S/Fe]> = +0.49 +- 0.15, consistent with what observed in field stars of the same metallicity. In the cluster 47 Tuc we measured S in 4 turn-off and 5 subgiant stars with a mean <[S/Fe]> = +0.18 +- 0.14. While this result is compatible with no star to star scatter we notice a statistically significant correlation of the sulphur abundance with the sodium abundance and a tentative correlation with the silicon abundance.

SBS 0335-052E+W: deep VLT/FORS+UVES spectroscopy of the pair of the lowest-metallicity blue compact dwarf galaxies

(abridged) We present deep archival VLT/FORS1+UVES spectroscopic observations of the system of two blue compact dwarf (BCD) galaxies SBS 0335-052E and SBS 0335-052W. Our aim is to derive element abundances in different HII regions of this unique system of galaxies and to study spatial abundance variations. We determine abundances of helium, nitrogen, oxygen, neon, sulfur, chlorine, argon and iron. The oxygen abundance in the brighter eastern galaxy varies in the range 7.11 to 7.32 in different HII regions supporting previous findings and suggesting the presence of oxygen abundance variations on spatial scales of ~1-2 kpc. The oxygen abundance in the brightest region No.1 of SBS 0335-052W is 7.22+/-0.07, consistent with previous determinations.Three other HII regions are much more metal-poor with an unprecedently low oxygen abundance of 12+logO/H=7.01+/-0.07 (region No.2), 6.98+/-0.06 (region No.3), and 6.86+/-0.14 (region No.4). These are the lowest oxygen abundances ever derived in emission-line galaxies. Helium abundances derived for the brightest HII regions of both galaxies are mutually consistent. We derive weighted mean He mass fractions of 0.2485+/-0.0012 and 0.2514+/-0.0012 for two different sets of HeI emissivities. The N/O abundance ratio in both galaxies is slightly higher than that derived for other BCDs with 12+logO/H<7.6. This implies that the N/O in extremely metal-deficient galaxies could increase with decreasing metallicity.

A SPECTROSCOPIC AND PHOTOMETRIC STUDY OF THE METAL-POOR, PULSATING, POST-ASYMPTOTIC GIANT BRANCH BINARY HD 46703

The metal-poor post-asymptotic giant branch (AGB) star HD 46703 is shown to be a single-line spectroscopic binary with a period of 600 days, a high velocity of –94 km s–1, and an orbital eccentricity of 0.3. Light-curve studies show that it also pulsates with a period of 29 days. High-resolution, high signal-to-noise spectra were used for a new abundance study. The atmospheric model determined is T eff = 6250 K, log g = 1.0, Vt = 3.0 km s–1, and a metal abundance of [M/H] = –1.5. A low carbon abundance and a lack of s-process element enhancement indicate that the star has not experienced a third dredge-up on the AGB. The sulfur and zinc abundances are high compared with iron, and the chemical abundances show a clear anti-correlation with condensation temperature. The abundance depletion pattern is similar to that seen in other post-AGB binaries, and, like them, is attributed to the chemical fractionation of refractory elements onto dust stored in a circumbinary disk and the re-accretion of volatiles in the stellar atmosphere. The infrared excess is small but the excess energy distribution is very similar to what can be expected from a disk. HD 46703 joins the growing list of depleted, post-AGB stars which are likely surrounded by a dusty and stable circumbinary disk.

The spectroscopic variability ofTeffand log gin the hot pulsating star β Cephei

Time resolved spectra of β Cep yield the following average results: T eff = 24000 ± 250 K, log g = 3.91 ± 0.05 and ζ =8.1 ± 0.9 km s -1 . Nitrogen, oxygen, neon, aluminium, silicon and sulfur abundances are solar while carbon, magnesium and iron are slightly underabundant. Pulsational amplitudes of ∇T eff ∼ 700 K and Alog g ∼ 0.2 dex are found from Hβ. The metal lines give similar amplitudes but centred on T eff ∼ 25 000 K. An upper limit of 1.0 km s -1 to the variability of the microturbulence is derived from the Si III triplet at 455 nm. The radial-velocity amplitude derived from the core of Hβ is ∼15 per cent greater than that from the metal lines.

Returning to Europa: can traces of surficial life be detected?

AbstractThere is at present a possibility for returning to Europa with LAPLACE, a mission to Europa and the Jupiter System for European Space Agency's Cosmic Vision Programme. The question of habitability by the identification of reliable bio-indicators is a major priority. We explain the options for approaching the question of selecting the right instrumentation for measuring the more abundant sulphur isotope, in spite of the fact that32S is isobaric (samem/z) with16O2. Two technologies are available for investigating the possible biogenicity of the surficial sulphur on the icy patches discovered by the Galileo mission. We argue that there is a need to use higher-order statistics in the data that are to be gathered with the instruments chosen for the payload (ion-traps for orbital measurements, or penetrators for surficial measurements). In particular, we argue in favour of data analysis taken from an orbital spacecraft that addresses fluctuations of the data retrieved, rather than the mean. For this purpose, we reconsider the significance of deviations of sulphur abundances relative to normal (meteoritic) values. In the present work, we consider the experimentally testable possibility of biogenically driven isotopic anomalies in the light of statistical data analysis. The fluctuation test that is being proposed in the context of future missions to Europa may well be appropriate to a laboratory experiment with sulphur-reducing bacteria with the corresponding isotopic fractionation.

The blue supergiant Sher 25 and its intriguing hourglass nebula

The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log[O/H] = 8.61 +/- 0.13 dex) is similar to that in the background nebula (8.56 +/- 0.07), suggesting the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 +/- 0.15, compared to the background value of 7.47 +/- 0.18. A new analysis of the stellar spectrum with the FASTWIND model atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher 25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50 M_sun, which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances.

Chemical Abundances and Dust in Planetary Nebulae in the Galactic Bulge

We present mid-infrared Spitzer spectra of eleven planetary nebulae in the Galactic Bulge. We derive argon, neon, sulfur, and oxygen abundances for them using mainly infrared line fluxes combined with some optical line fluxes from the literature. Due to the high extinction toward the Bulge, the infrared spectra allow us to determine abundances for certain elements more accurately that previously possible with optical data alone. Abundances of argon and sulfur (and in most cases neon and oxygen) in planetary nebulae in the Bulge give the abundances of the interstellar medium at the time their progenitor stars formed; thus these abundances give information about the formation and evolution of the Bulge. The abundances of Bulge planetary nebulae tend to be slightly higher than those in the Disk on average, but they do not follow the trend of the Disk planetary nebulae, thus confirming the difference between Bulge and Disk evolution. Additionally, the Bulge planetary nebulae show peculiar dust properties compared to the Disk nebulae. Oxygen-rich dust feature (crystalline silicates) dominate the spectra of all of the Bulge planetary nebulae; such features are more scarce in Disk nebulae. Additionally, carbon-rich dust features (polycyclic aromatic hydrocarbons) appear in roughly half of the Bulge planetary nebulae in our sample, which is interesting in light of the fact that this dual chemistry is comparatively rare in the Milky Way as a whole.

Chemical Composition and Mixing in Giant HiiRegions: NGC 3603, 30 Doradus, and N66

We investigate the chemical abundances of NGC 3603 in the Milky Way, of 30 Doradus in the Large Magellanic Cloud, and of N66 in the Small Magellanic Cloud. Mid-infrared observations with the Infrared Spectrograph on board the Spitzer Space Telescope allow us to probe the properties of distinct physical regions within each object, the central ionizing cluster, the surrounding ionized gas, photodissociation regions, and buried stellar clusters. We detect [S III], [S IV], [Ar III], [Ne II], [Ne III], [Fe II], and [Fe III] lines and derive the ionic abundances. Based on the ionic abundance ratio (Ne III/H)/(S III/H), we find that the gas observed in the MIR is characterized by a lower degree of ionization than the gas observed in the optical spectra. We compute the elemental abundances of Ne, S, Ar, and Fe. We find that the ?-elements Ne, S, and Ar scale with each other. Our determinations agree well with the abundances derived from the optical. The Ne/S ratio is higher than the solar value in the three giant H II regions and points toward a moderate depletion of sulfur on dust grains. We find that the neon and sulfur abundances display a remarkably small dispersion (0.11 dex in 15 positions in 30 Doradus), suggesting a relatively homogeneous ISM, even though small-scale mixing cannot be ruled out.

Distinguishing solid bitumens formed by thermochemical sulfate reduction and thermal chemical alteration

Insoluble solid bitumens are organic residues that can form by the thermal chemical alteration (TCA) or thermochemical sulfate reduction (TSR) of migrated petroleum. TCA may actually encompass several low temperature processes, such as biodegradation and asphaltene precipitation, followed by thermal alteration. TSR is an abiotic redox reaction where petroleum is oxidized by sulfate. It is difficult to distinguish solid bitumens associated with TCA of petroleum from those associated with TSR when both processes occur at relatively high temperature. The focus of the present work was to characterize solid bitumen samples associated with TCA or TSR using X-ray photoelectron spectroscopy (XPS). XPS is a surface analysis conducted on either isolated or in situ (>25 μm diameter) solid bitumen that can provide the relative abundance and chemical speciation of carbon, organic and inorganic heteroatoms (NSO). In this study, naturally occurring solid bitumens from three locations, Nisku Fm. Brazeau River area (TSR-related), LaBarge Field Madison Fm. (TSR-related), and the Alaskan Brooks range (TCA-related), are compared to organic solids generated during laboratory simulation of the TSR and TCA processes. The abundance and chemical nature of organic nitrogen and sulfur in solid bitumens can be understood in terms of the nature of (1) petroleum precursor molecules, (2) the concentration of nitrogen by way of thermal stress and (3) the mode of sulfur incorporation. TCA solid bitumens originate from polar materials that are initially rich in sulfur and nitrogen. Aromaticity and nitrogen increase as thermal stress cleaves aliphatic moieties and condensation reactions take place. Organic sulfur in TCA organic solids remains fairly constant with increasing maturation (<3.4 sulfurs per 100 carbons) due to offsetting preservation and H 2S elimination reactions. In contrast, TSR solid bitumens are sulfur rich and nitrogen poor solids. These heteroatom distributions are attributed to the ability of TSR to incorporate copious amounts of inorganic sulfur (>3.5 to ∼17 sulfur per 100 carbons) into aromatic structures and to the low levels of nitrogen in their hydrocarbon precursors. Hence, XPS results provide organic chemical composition information that helps to distinguish whether solid bitumen, either in situ or removed and concentrated from the rock matrix, was formed via the TCA or TRS process.

Laboratory simulations of sulfur depletion at Eros

The X-ray spectrometer of the Near-Earth Asteroid Rendezvous (NEAR) mission discovered a low abundance of sulfur on the surface of asteroid Eros, which is seemingly inconsistent with the match of the overall surface composition to that of ordinary chondrites. Since troilite, FeS, is the primary sulfur-bearing mineral in ordinary chondrites, we investigated the hypothesis that sulfur loss from surface FeS could result from ‘space weathering’ by impact of solar wind ions and micrometeorites. We performed laboratory studies on the chemical alteration of FeS by 4 keV ions simulating exposure to the solar wind and by nanosecond laser pulses simulating pulsed heating by micrometeorite impact. We found that the combination of laser irradiation followed by ion impact lowers the S:Fe atomic ratio on the surface by a factor of up to 2.5, which is consistent with the value of at least 1.5 deduced from the NEAR measurements. Thus, our results support the hypothesis that the low abundance of sulfur at the surface of Eros is caused by space weathering.

Photoionization Models Applied to Planetary Nebulae

Good to excellent photoionization models based on the Cloudy code (from Ferland and coworkers) were obtained for 13 out of 19 spectra of planetary nebulae (PNs). Results are deficient when the slit is missing most of the in-depth extent of the ionized region. Features that can be associated to shock excitation and abnormally large helium abundances are found when this is the case. Models assume that the exciting star is a Rauch photosphere illuminating a static uniform density spherical shell. Model central stars lie close to a 2.5 M☉ post-AGB theoretical evolutionary track in the H-R diagram (from Vassiliadis and Wood), with implied PN ages between 1000 and 7000 yr. Observed and modeled nebular temperatures derived from [N II] λ λ (6548 + 6584)/λ 5755 agree within 10%, but models usually underestimate temperatures found from [O III] λ λ (4959 + 5007)/λ 4363, more so when the slit does not cover the in-depth extent of the ionized region. Helium, nitrogen, oxygen, neon, sulfur, chlorine, and argon model abundances are uncertain at the 15%, 15%, 10%, 7%, 30%, 5%, and 7% levels, respectively. The following relationships between chemical elements are found: He tends to be more abundant when N/O is large; there is a loose anticorrelation between N/O and O/H; N/C and C/H are anticorrelated; and the sum of the carbon, nitrogen, and oxygen abundances is larger in carbon-rich objects. Finally, it is shown that neon abundance in PNs has been overestimated, and an alternative ionization correction factor is provided.

A Multiwavelength Analysis of the Halo Planetary Nebula DdDm‐1

We present new HST optical imagery as well as new UV and IR spectroscopic data obtained with the Hubble Space Telescope and Spitzer Space Telescope, respectively, of the halo planetary nebula DdDm-1. For the first time we present a resolved image of this object, which indicates that the morphology of DdDm-1 can be described as two orthogonal elliptical components in the central part surrounded by an extended halo. The extent of the emission is somewhat larger than was previously reported in the literature. We combine the spectral data with our own previously published optical measurements to derive nebular abundances of He, C, N, O, Ne, Si, S, Cl, Ar, and Fe. The metallicity, as gauged by oxygen, is found to be 0.60 dex below the solar value, confirming DdDm-1's status as a halo PN. In addition, we find that Si and Fe are markedly underabundant, suggesting their depletion onto dust. The very low C/O ratio suggests that the chemistry of the nebula should be consistent with an oxygen-rich environment. With regard to the unexpectedly low S abundance relative to O often seen in PNe, we find that the sulfur abundance of DdDm-1 is only slightly below the value expected based on the normal lockstep behavior between S and O observed in H II regions and blue compact galaxies. We performed a photoionization model analysis from which we inferred a central star effective temperature and luminosity of 55,000 K and 1000 L☉, respectively, implying an initial progenitor mass of <1 M☉. Finally, we report on a new radial velocity determination from echelle observations.

Elemental Abundances of Blue Compact Dwarfs from Mid‐Infrared Spectroscopy withSpitzer

We present a study of elemental abundances in a sample of 13 blue compact dwarf (BCD) galaxies, using the ~10-37 μm high-resolution spectra obtained with Spitzer IRS. We derive the abundances of neon and sulfur for our sample using the infrared fine-structure lines probing regions which may be obscured by dust in the optical and compare our results with similar infrared studies of starburst galaxies from ISO. We find a good correlation between the neon and sulfur abundances, although sulfur is underabundant relative to neon with respect to the solar value. A comparison of the elemental abundances (neon and sulfur) measured from the infrared data with those derived from the optical (neon, sulfur, and oxygen) studies reveals a good overall agreement for sulfur, while the infrared-derived neon abundances are slightly higher than the optical values. This indicates either that the metallicities of dust-enshrouded regions in BCDs are similar to the optically accessible regions, or that if they are different they do not contribute substantially to the total infrared emission of the host galaxy.

Sulfur abundance of asteroid 25143 Itokawa observed by X-ray fluorescence spectrometer onboard Hayabusa

Abstract The Japanese Hayabusa spacecraft successfully carried out in situ observations of S-class asteroid 25143 Itokawa, including the surface major elemental analysis with the X-ray fluorescence spectrometer (XRSHayabusa). Our previous results for the X-ray experiments (Okada et al., 2006a) indicated that major elemental ratios of Mg/Si and Al/Si on the surface of Itokawa resemble ordinary LL- or L-chondrites more than any other meteorite analogues. In the NEAR Shoemaker observations of S-class asteroid 433 Eros, the results of X-ray fluorescence observations indicated the depletion of sulfur, probably reflecting impact-induced volatilization, photoor ion-induced sputtering at the surface, or the loss of FeS-rich materials due to partial melting. Here, we determined the elemental abundance of sulfur (S) on the surface of Itokawa, in addition to that of Mg, Al, and Si, and its regional variation using XRS-Hayabusa observations. In particular, we carefully corrected the fluctuation of solar X-rays, variation of surface geometry, and sensor response function in this analysis, and thus we believe that the results are more accurate than those of our previous report. In this study, the upper and lower limits for Mg/Si, Al/Si, and S/Si overlap those of meteorite analogues for ordinary chondrites or primitive achondrites. In terms of the major elemental composition, Itokawa is best classified as a ordinary chondrite or a primitive achondrite. Our models do not include the mineral mixing effects. With the effects, the abundance of sulfur is expected to be 30% lower than our results. Hence, we conclude that the abundance of sulfur on the surface of Itokawa is almost equal to or even lower than the average abundance in ordinary chondrites. Although the abundances for Mg and Si are globally homogeneous, best-fit or upper limits of mass fraction for Al and S vary in local areas. There is a negative correlation (−0.92) for Al/Si vs. S/Si in ten facets. In particular, the area with the lowest sulfur, accompanied with enriched aluminum, is found in Arcoona, close to a cratered area. Therefore, aluminum enrichment and sulfur depletion features may support events of partial melting on the parent body of Itokawa or aluminum-rich material impacts on the surface of Itokawa. In some areas, Itokawa has a brighter geometric albedo and color variation. Little altered, fresh material may be exposed in these portions of the surface. The sulfur abundance on the surface appears to vary between little and highly altered areas by space weathering. Thus, the sulfur regional variation in our result may reflect the heterogeneity of a surface altered by space weathering.