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The deuterium-to-oxygen ratio in the local interstellar medium from FUSE observations
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Planetary and Space Science 50 (2002) 1169 – 1172 www.elsevier.com/locate/pss
The deuterium-to-oxygen ratio in the local interstellar medium from FUSE observations G. H,ebrarda;∗ , S.D. Friedmanb , J.W. Krukb , N. Lehnerb , M. Lemoinea , J.L. Linskyc , H.W. Moosb , C.M. Oliveirab , K.R. Sembachb , G. Sonnebornd , A. Vidal-Madjara , B.E. Woodc a Institut
d’Astrophysique de Paris, CNRS, 98 bis Boulevard Arago, F-75014 Paris, France of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA c JILA, University of Colorado and NIST, Campus Box 440, Boulder, CO 80309-0440, USA d Laboratory for Astronomy and Solar Physics, NASA/GSFC, Code 681, Greenbelt, MD 20771, USA b Department
Received 12 November 2001; received in revised form 4 March 2002; accepted 11 March 2002
Abstract Since HI, OI, and DI have nearly the same ionization potential, the deuterium-to-oxygen ratio (D/O) is an important tracer of the D/H ratio and its putative spatial variations. D/O is indeed very sensitive to astration, both because of deuterium destruction and oxygen production. Here, we present DI, OI, and NI interstellar column density measurements performed with the Far Ultraviolet Spectroscopic Explorer (FUSE) on eight nearby lines of sight. The Arst results of this survey show that D/O is a better D/H proxy than D/N, and that D/O is constant in the local interstellar medium. The mean value is D=O = 3:81(±0:18) × 10−2 (1). This result supports both D/H and O/H stability in the LISM. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: ISM: Abundances; ISM: Clouds; cosmology: Observations; ultraviolet: ISM; stars: White dwarfs
1. Presentation Deuterium abundance is a key measurement for cosmology and galactic chemical evolution. Indeed, deuterium is believed to be entirely produced during the Big Bang Nucleosynthesis and then steadily destroyed by astration. Deuterium abundance is usually measured by number in comparison with hydrogen. Although the evolution of the deuterium abundance seems to be qualitatively understood, D/H measurements in diGerent astrophysical sites have not converged to deAnite values and show some dispersion (e.g. Lemoine et al., 1999). An accurate determination of the present-day abundance of deuterium in the local interstellar medium (LISM) is one of the main objectives of the Far Ultraviolet Spectroscopic Explorer (FUSE) mission, which was successfully
This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to US participants has been provided by NASA contract NAS5-32985. French participants are supported by CNES. ∗ Corresponding author. Fax: +33-1-44-32-80-01. E-mail address: [email protected] (G. H,ebrard).
launched on June 24, 1999 (Moos et al., 2000). Previous D/H measurements in the LISM show some dispersion, which may result from spatial variations due to some unknown physical processes or underestimation of systematic errors. There is still considerable debate over these two interpretations, and the Anal resolution of the issue may have implications for understanding the physics of the interstellar medium, as well as the baryonic density inferred from D/H measurements. One of the challenges of D/H measurements is to evaluate simultaneously HI and DI column densities, which are diGerent by about 5 orders of magnitudes. It could lead to systematic errors, due to the fact that all lines from the same species may lie on the non-linear part of the curve of growth, or that there may be clouds in which HI column densities are detectable, but whose DI column densities are below the detection limit. Here, we report the Arst results of a survey of the D/O ratio in the LISM performed with FUSE. Many of the diJculties in obtaining accurate D/H measurements may be avoided by measuring D/O (e.g. Timmes et al., 1997): indeed the average D/O ratio in the ISM is of order of a few
0032-0633/02/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 2 - 0 6 3 3 ( 0 2 ) 0 0 0 7 8 - 8
4:6 ± 0:5 3:5 ± 0:4 3:9 ± 0:6 4:0 ± 0:6 3:5 ± 0:3 4:9 ± 1:5 3:9 ± 0:8 4:5 ± 1:3 4:4 ± 0:4 3:4 ± 0:4 3:3 ± 0:5 4:4 ± 0:6 2:7 ± 0:3 3:8 ± 1:2 1:4 ± 0:5 1:8 ± 0:7 14:49 ± 0:04 14:86 ± 0:04 15:26 ± 0:04 15:34 ± 0:04 15:51 ± 0:03 15:57 ± 0:08 15:90 ± 0:06 15:88 ± 0:06 are photometric (Dph ) or from Hipparcos parallax (Dpa ). densities N (in cm−2 ); 1 error bars. b Column
DA1 DA1 DA1 DA1 DO DA1 sdO DA1 HZ 43 A G191 − B2B WD 0621 − 376 WD 2211 − 495 WD 1634 − 573 GD 246 CPD − 31 1701 WD 1631 + 781
a Distances
13:15 ± 0:02 13:40 ± 0:04 13:85 ± 0:05 13:94 ± 0:05 14:05 ± 0:03 14:26 ± 0:08 14:49 ± 0:06 14:53 ± 0:07 68 ± 15ph 69 ± 16pa 78ph 53ph 37 ± 3pa 79ph 131 ± 28pa 67ph
Type Target
Fig. 1. Location of the targets. Coordinates (deg.) are galactic.
Table 1 Targets
lII (deg.)
bII (deg.)
Column density measurements have been obtained from interstellar spectral lines, observed in absorption on the lines of sight to the eight targets. We focus here on results on DI, OI, and NI column densities. FUSE is particularly well adapted for the measurement of these column densities since numerous transitions of these species are present in the L spectral window, with a large range of FUSE 905 –1187 A oscillator strengths. Several techniques were used to determine the DI, NI, and OI column densities (Moos et al., 2002): proAle
+84:2 +7:1 −21.4 −52.6 −7.0 −45.1 −5.5 +33:6
3. Data analysis
log N (DI)b
log N (NI)b
log N (OI)b
D=N × 10b
We present here Arst results obtained toward eight targets: seven white dwarfs and one sub-dwarf (see Table 1 and Fig. 1). Observations were performed mainly in 2000, as part of the FUSE Science Team D/H program and the FUSE calibration program. The one-dimensional spectra were extracted from the two-dimensional detector images and calibrated using the CALFUSE pipeline. Each FUSE observation is split up into individual exposures. They were co-added separately for each channel (SiC1, SiC2, LiF1, and LiF2) and for a given slit, after correcting for zero-point wavelength oGsets between individual calibrated exposures. A sample of a spectrum is shown in Fig. 2.
54.1 155.9 245.4 345.8 329.9 87.2 246.5 111.3
2. Observations and data processing
13:51 ± 0:03 13:87 ± 0:04 14:34 ± 0:05 14:30 ± 0:03 14:62 ± 0:04 14:68 ± 0:10 15:34 ± 0:09 15:28 ± 0:10
D=O × 102b
Reference
percent, instead of a few 10−5 for D/H, and many OI absorption lines with diGerent oscillator strengths are present in the FUSE bandpass. Furthermore, OI is believed to be a good tracer of HI in the Galactic disk (Meyer et al., 1998; Andr,e et al., in prep.) since both species have nearly the same ionization potential, and neutral forms dominate over ionized forms in the diGuse interstellar medium. Moreover, D/O is very sensitive to astration, both from D destruction and O production.
Kruk et al. (2002) Lemoine et al. (2002) Lehner et al. (2002) H,ebrard et al. (2002a) Wood et al. (2002) Oliveira et al. (in prep.) H,ebrard et al. (in prep.) H,ebrard et al. (in prep.)
G. H=ebrard et al. / Planetary and Space Science 50 (2002) 1169 – 1172
d (pc)a
1170
G. H=ebrard et al. / Planetary and Space Science 50 (2002) 1169 – 1172
1171
Fig. 2. Example of a spectrum obtained with FUSE. The target is the white dwarf WD 2211 − 495. This spectrum is a sample of that observed on the segment SiC1B through the LWRS slit. The HI Lyman series is indicated and the positions of the DI, OI, and NI interstellar absorption lines are marked.
Fig. 3. D/O ratios in the local interstellar medium. The weighted mean of these eight values is (D=O)LISM = 3:81(±0:18) × 10−2 . All the plotted error bars are 1.
Fig. 4. D/N ratios in the local interstellar medium. The plotted error bars are 1.
Atting, single-component curves of growth Atted to the measured equivalent widths, and analysis of the apparent optical depths of the weak lines. Description of these methods can be found in the papers devoted to the analysis of the individual sight lines (Kruk et al., 2002; H,ebrard et al., 2002a; Lehner et al., 2002; Lemoine et al., 2002; Wood et al., 2002). The Arst results toward GD 246, CPD − 31 1701, and WD 1631+781 reported here were obtained only from the Atting method described in H,ebrard et al. (2002a); data analysis for these three objects (including extra observations) will be discussed in forthcoming papers (Oliveira et al., in prep.; H,ebrard et al., in prep.).
fact that OI is a better tracer of HI than NI, due to ionization eGects (Jenkins et al., 2000). The weighted mean of D/O and the standard deviation of the mean are
4. Results
The D/O stability in the LISM argues against variations of (D=H)LISM . Indeed, the only possibility to have both D/O stability and D/H variations would be that D/H and O/H vary precisely in the same way as to cause D/O to remain constant. That seems improbable since (i) O/H appears to be uniform in the ISM over paths of several hundreds parsecs
The results are presented in Table 1. Fig. 3 presents the D/O ratio as a function of the DI column density. D/O appears to be remarkably constant in the LISM, contrary to the D/N ratio (Fig. 4). The diGerence is probably due to the
(D=O)LISM = 3:81(±0:18) × 10−2 (1): Considering the individual D/O measurements and the weighted mean, the total 2 = 5:6 for 7 degrees of freedom gives a reduced 2 of 0.8. Therefore, there is no evidence for variation of D/O in the LISM. 5. Discussion and conclusion
1172
G. H=ebrard et al. / Planetary and Space Science 50 (2002) 1169 – 1172
(e.g. Meyer et al., 1998; Andr,e et al., in prep.), and (ii) astration should lead to an anti-correlation of DI and OI abundances. The stability of D/O in the LISM appears rather as a strong argument which support both D/H and O/H spatial stability in the LISM. The D/O ratio could be used to estimate D/H if an assumption on O/H is made. By assuming the value O=H = 3:19(±0:14) × 10−4 found by Meyer et al. (1998), we obtain D=H = 1:22(±0:08) × 10−5 (1). This value is slightly lower than the average value of Linsky (1998) obtained from the comparison of HST data for 12 nearby sightlines: D=H = 1:5 ± 0:1 × 10−5 (1). This latter D/H value would correspond to D=O = 4:8(±0:4) × 10−2 (1, according to the O/H Meyer et al., 1998 value). First FUSE results obtained for log N (DI) ¿ 15 and d ¿ 100 pc toward BD + 28◦ 4211 [D=O = 5:6(±0:7) × 10−2 (1); Sonneborn et al., 2002] and Feige 110 [D=O = 5:5(±0:8) × 10−2 (1); Friedman et al., 2002] suggest that D/O variations may occur at larger column densities (larger pathlengths). Such a trend is expected if oxygen depletion onto dust grains increase for denser clouds (Cartledge et al., 2001). Indeed, the results presented here refer only to the gaseous forms of H, D, and O, and approximately 30 – 40% of the total interstellar oxygen is probably in the solid phase (Meyer et al., 1998; SoAa and Meyer, 2001; Allende Prieto et al., 2001). Thus, D/O studies should be extended to more distant lines of sight. References Allende Prieto, C., et al., 2001. The forbidden abundance of oxygen in the Sun. Astrophys. J. 556, L63.
Andr,e, M., et al. Oxygen gas phase abundance revisited, in preparation. Cartledge, S.I.B., et al., 2001. Space telescope imaging spectrograph observations of interstellar oxygen and krypton in translucent clouds. Astrophys. J. 562, 394. Friedman, S.D., et al., 2002. Deuterium and oxygen toward feige 110: results from the FUSE mission. Astrophys. J. Suppl. 140, 36. H,ebrard, G., et al., 2002a. Deuterium abundance toward WD 2211 − 495: results from the FUSE mission. Astrophys. J. Suppl. 140, 103. H,ebrard, G., et al., in preparation. Jenkins, E.B., et al., 2000. The ionization of the local interstellar medium as revealed by far ultraviolet spectroscopic explorer observations of N, O, and Ar toward white dwarf stars. Astrophys. J. 538, L81. Kruk, J.W., et al., 2002. Interstellar deuterium, nitrogen, and oxygen towards HZ 43A: results from the FUSE mission. Astrophys. J. Suppl. 140, 19. Lehner, N., et al., 2002. Deuterium toward the white dwarf WD 0621 − 376: results from the FUSE mission. Astrophys. J. Suppl. 140, 81. Lemoine, M., et al., 1999. Deuterium abundances. New Astron. 4, 231. Lemoine, M., et al., 2002. Deuterium abundance toward G191-B2B: results from the FUSE mission. Astrophys. J. Suppl. 140, 67. Linsky, J.L., 1998. Deuterium abundance in the local ISM and possible spatial variations. Space Sci. Rev. 84, 285. Meyer, D.M., et al., 1998. The deAnitive abundance of interstellar oxygen. Astrophys. J. 493, 222. Moos, H.W., et al., 2000. Overview of the far ultraviolet spectroscopic explorer mission. Astrophys. J. 538, L1. Moos, H.W., et al., 2002. Abundances of deuterium, oxygen, and nitrogen in the local interstellar medium: overview of Arst results from the FUSE mission. Astrophys. J. Suppl. 140, 3. Oliveira, C., et al. in preparation. SoAa, U.J., Meyer, D.M., 2001. Interstellar abundance standards revisited. Astrophys. J. 554, L221 (Erratum: Astrophys. J. 558, L147). Sonneborn, G., et al., 2002. Interstellar deuterium, nitrogen, and oxygen abundances toward BD+28◦ 4211: Arst results from the FUSE mission. Astrophys. J. Suppl. 140, 51. Timmes, F.X., Truran, J.W., Lauroesch, J.T., York, D.G., 1997. Light-element abundances from z = 0 to z = 5. Astrophys. J. 476, 464. Wood, B.E., et al., 2002. Deuterium abundance toward WD 1634 − 573: results from the FUSE mission. Astrophys. J. Suppl. 140, 91.
Planetary and Space Science 50 (2002) 1169 – 1172 www.elsevier.com/locate/pss
The deuterium-to-oxygen ratio in the local interstellar medium from FUSE observations G. H,ebrarda;∗ , S.D. Friedmanb , J.W. Krukb , N. Lehnerb , M. Lemoinea , J.L. Linskyc , H.W. Moosb , C.M. Oliveirab , K.R. Sembachb , G. Sonnebornd , A. Vidal-Madjara , B.E. Woodc a Institut
d’Astrophysique de Paris, CNRS, 98 bis Boulevard Arago, F-75014 Paris, France of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA c JILA, University of Colorado and NIST, Campus Box 440, Boulder, CO 80309-0440, USA d Laboratory for Astronomy and Solar Physics, NASA/GSFC, Code 681, Greenbelt, MD 20771, USA b Department
Received 12 November 2001; received in revised form 4 March 2002; accepted 11 March 2002
Abstract Since HI, OI, and DI have nearly the same ionization potential, the deuterium-to-oxygen ratio (D/O) is an important tracer of the D/H ratio and its putative spatial variations. D/O is indeed very sensitive to astration, both because of deuterium destruction and oxygen production. Here, we present DI, OI, and NI interstellar column density measurements performed with the Far Ultraviolet Spectroscopic Explorer (FUSE) on eight nearby lines of sight. The Arst results of this survey show that D/O is a better D/H proxy than D/N, and that D/O is constant in the local interstellar medium. The mean value is D=O = 3:81(±0:18) × 10−2 (1). This result supports both D/H and O/H stability in the LISM. ? 2002 Elsevier Science Ltd. All rights reserved. Keywords: ISM: Abundances; ISM: Clouds; cosmology: Observations; ultraviolet: ISM; stars: White dwarfs
1. Presentation Deuterium abundance is a key measurement for cosmology and galactic chemical evolution. Indeed, deuterium is believed to be entirely produced during the Big Bang Nucleosynthesis and then steadily destroyed by astration. Deuterium abundance is usually measured by number in comparison with hydrogen. Although the evolution of the deuterium abundance seems to be qualitatively understood, D/H measurements in diGerent astrophysical sites have not converged to deAnite values and show some dispersion (e.g. Lemoine et al., 1999). An accurate determination of the present-day abundance of deuterium in the local interstellar medium (LISM) is one of the main objectives of the Far Ultraviolet Spectroscopic Explorer (FUSE) mission, which was successfully
This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to US participants has been provided by NASA contract NAS5-32985. French participants are supported by CNES. ∗ Corresponding author. Fax: +33-1-44-32-80-01. E-mail address: [email protected] (G. H,ebrard).
launched on June 24, 1999 (Moos et al., 2000). Previous D/H measurements in the LISM show some dispersion, which may result from spatial variations due to some unknown physical processes or underestimation of systematic errors. There is still considerable debate over these two interpretations, and the Anal resolution of the issue may have implications for understanding the physics of the interstellar medium, as well as the baryonic density inferred from D/H measurements. One of the challenges of D/H measurements is to evaluate simultaneously HI and DI column densities, which are diGerent by about 5 orders of magnitudes. It could lead to systematic errors, due to the fact that all lines from the same species may lie on the non-linear part of the curve of growth, or that there may be clouds in which HI column densities are detectable, but whose DI column densities are below the detection limit. Here, we report the Arst results of a survey of the D/O ratio in the LISM performed with FUSE. Many of the diJculties in obtaining accurate D/H measurements may be avoided by measuring D/O (e.g. Timmes et al., 1997): indeed the average D/O ratio in the ISM is of order of a few
0032-0633/02/$ - see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 2 - 0 6 3 3 ( 0 2 ) 0 0 0 7 8 - 8
4:6 ± 0:5 3:5 ± 0:4 3:9 ± 0:6 4:0 ± 0:6 3:5 ± 0:3 4:9 ± 1:5 3:9 ± 0:8 4:5 ± 1:3 4:4 ± 0:4 3:4 ± 0:4 3:3 ± 0:5 4:4 ± 0:6 2:7 ± 0:3 3:8 ± 1:2 1:4 ± 0:5 1:8 ± 0:7 14:49 ± 0:04 14:86 ± 0:04 15:26 ± 0:04 15:34 ± 0:04 15:51 ± 0:03 15:57 ± 0:08 15:90 ± 0:06 15:88 ± 0:06 are photometric (Dph ) or from Hipparcos parallax (Dpa ). densities N (in cm−2 ); 1 error bars. b Column
DA1 DA1 DA1 DA1 DO DA1 sdO DA1 HZ 43 A G191 − B2B WD 0621 − 376 WD 2211 − 495 WD 1634 − 573 GD 246 CPD − 31 1701 WD 1631 + 781
a Distances
13:15 ± 0:02 13:40 ± 0:04 13:85 ± 0:05 13:94 ± 0:05 14:05 ± 0:03 14:26 ± 0:08 14:49 ± 0:06 14:53 ± 0:07 68 ± 15ph 69 ± 16pa 78ph 53ph 37 ± 3pa 79ph 131 ± 28pa 67ph
Type Target
Fig. 1. Location of the targets. Coordinates (deg.) are galactic.
Table 1 Targets
lII (deg.)
bII (deg.)
Column density measurements have been obtained from interstellar spectral lines, observed in absorption on the lines of sight to the eight targets. We focus here on results on DI, OI, and NI column densities. FUSE is particularly well adapted for the measurement of these column densities since numerous transitions of these species are present in the L spectral window, with a large range of FUSE 905 –1187 A oscillator strengths. Several techniques were used to determine the DI, NI, and OI column densities (Moos et al., 2002): proAle
+84:2 +7:1 −21.4 −52.6 −7.0 −45.1 −5.5 +33:6
3. Data analysis
log N (DI)b
log N (NI)b
log N (OI)b
D=N × 10b
We present here Arst results obtained toward eight targets: seven white dwarfs and one sub-dwarf (see Table 1 and Fig. 1). Observations were performed mainly in 2000, as part of the FUSE Science Team D/H program and the FUSE calibration program. The one-dimensional spectra were extracted from the two-dimensional detector images and calibrated using the CALFUSE pipeline. Each FUSE observation is split up into individual exposures. They were co-added separately for each channel (SiC1, SiC2, LiF1, and LiF2) and for a given slit, after correcting for zero-point wavelength oGsets between individual calibrated exposures. A sample of a spectrum is shown in Fig. 2.
54.1 155.9 245.4 345.8 329.9 87.2 246.5 111.3
2. Observations and data processing
13:51 ± 0:03 13:87 ± 0:04 14:34 ± 0:05 14:30 ± 0:03 14:62 ± 0:04 14:68 ± 0:10 15:34 ± 0:09 15:28 ± 0:10
D=O × 102b
Reference
percent, instead of a few 10−5 for D/H, and many OI absorption lines with diGerent oscillator strengths are present in the FUSE bandpass. Furthermore, OI is believed to be a good tracer of HI in the Galactic disk (Meyer et al., 1998; Andr,e et al., in prep.) since both species have nearly the same ionization potential, and neutral forms dominate over ionized forms in the diGuse interstellar medium. Moreover, D/O is very sensitive to astration, both from D destruction and O production.
Kruk et al. (2002) Lemoine et al. (2002) Lehner et al. (2002) H,ebrard et al. (2002a) Wood et al. (2002) Oliveira et al. (in prep.) H,ebrard et al. (in prep.) H,ebrard et al. (in prep.)
G. H=ebrard et al. / Planetary and Space Science 50 (2002) 1169 – 1172
d (pc)a
1170
G. H=ebrard et al. / Planetary and Space Science 50 (2002) 1169 – 1172
1171
Fig. 2. Example of a spectrum obtained with FUSE. The target is the white dwarf WD 2211 − 495. This spectrum is a sample of that observed on the segment SiC1B through the LWRS slit. The HI Lyman series is indicated and the positions of the DI, OI, and NI interstellar absorption lines are marked.
Fig. 3. D/O ratios in the local interstellar medium. The weighted mean of these eight values is (D=O)LISM = 3:81(±0:18) × 10−2 . All the plotted error bars are 1.
Fig. 4. D/N ratios in the local interstellar medium. The plotted error bars are 1.
Atting, single-component curves of growth Atted to the measured equivalent widths, and analysis of the apparent optical depths of the weak lines. Description of these methods can be found in the papers devoted to the analysis of the individual sight lines (Kruk et al., 2002; H,ebrard et al., 2002a; Lehner et al., 2002; Lemoine et al., 2002; Wood et al., 2002). The Arst results toward GD 246, CPD − 31 1701, and WD 1631+781 reported here were obtained only from the Atting method described in H,ebrard et al. (2002a); data analysis for these three objects (including extra observations) will be discussed in forthcoming papers (Oliveira et al., in prep.; H,ebrard et al., in prep.).
fact that OI is a better tracer of HI than NI, due to ionization eGects (Jenkins et al., 2000). The weighted mean of D/O and the standard deviation of the mean are
4. Results
The D/O stability in the LISM argues against variations of (D=H)LISM . Indeed, the only possibility to have both D/O stability and D/H variations would be that D/H and O/H vary precisely in the same way as to cause D/O to remain constant. That seems improbable since (i) O/H appears to be uniform in the ISM over paths of several hundreds parsecs
The results are presented in Table 1. Fig. 3 presents the D/O ratio as a function of the DI column density. D/O appears to be remarkably constant in the LISM, contrary to the D/N ratio (Fig. 4). The diGerence is probably due to the
(D=O)LISM = 3:81(±0:18) × 10−2 (1): Considering the individual D/O measurements and the weighted mean, the total 2 = 5:6 for 7 degrees of freedom gives a reduced 2 of 0.8. Therefore, there is no evidence for variation of D/O in the LISM. 5. Discussion and conclusion
1172
G. H=ebrard et al. / Planetary and Space Science 50 (2002) 1169 – 1172
(e.g. Meyer et al., 1998; Andr,e et al., in prep.), and (ii) astration should lead to an anti-correlation of DI and OI abundances. The stability of D/O in the LISM appears rather as a strong argument which support both D/H and O/H spatial stability in the LISM. The D/O ratio could be used to estimate D/H if an assumption on O/H is made. By assuming the value O=H = 3:19(±0:14) × 10−4 found by Meyer et al. (1998), we obtain D=H = 1:22(±0:08) × 10−5 (1). This value is slightly lower than the average value of Linsky (1998) obtained from the comparison of HST data for 12 nearby sightlines: D=H = 1:5 ± 0:1 × 10−5 (1). This latter D/H value would correspond to D=O = 4:8(±0:4) × 10−2 (1, according to the O/H Meyer et al., 1998 value). First FUSE results obtained for log N (DI) ¿ 15 and d ¿ 100 pc toward BD + 28◦ 4211 [D=O = 5:6(±0:7) × 10−2 (1); Sonneborn et al., 2002] and Feige 110 [D=O = 5:5(±0:8) × 10−2 (1); Friedman et al., 2002] suggest that D/O variations may occur at larger column densities (larger pathlengths). Such a trend is expected if oxygen depletion onto dust grains increase for denser clouds (Cartledge et al., 2001). Indeed, the results presented here refer only to the gaseous forms of H, D, and O, and approximately 30 – 40% of the total interstellar oxygen is probably in the solid phase (Meyer et al., 1998; SoAa and Meyer, 2001; Allende Prieto et al., 2001). Thus, D/O studies should be extended to more distant lines of sight. References Allende Prieto, C., et al., 2001. The forbidden abundance of oxygen in the Sun. Astrophys. J. 556, L63.
Andr,e, M., et al. Oxygen gas phase abundance revisited, in preparation. Cartledge, S.I.B., et al., 2001. Space telescope imaging spectrograph observations of interstellar oxygen and krypton in translucent clouds. Astrophys. J. 562, 394. Friedman, S.D., et al., 2002. Deuterium and oxygen toward feige 110: results from the FUSE mission. Astrophys. J. Suppl. 140, 36. H,ebrard, G., et al., 2002a. Deuterium abundance toward WD 2211 − 495: results from the FUSE mission. Astrophys. J. Suppl. 140, 103. H,ebrard, G., et al., in preparation. Jenkins, E.B., et al., 2000. The ionization of the local interstellar medium as revealed by far ultraviolet spectroscopic explorer observations of N, O, and Ar toward white dwarf stars. Astrophys. J. 538, L81. Kruk, J.W., et al., 2002. Interstellar deuterium, nitrogen, and oxygen towards HZ 43A: results from the FUSE mission. Astrophys. J. Suppl. 140, 19. Lehner, N., et al., 2002. Deuterium toward the white dwarf WD 0621 − 376: results from the FUSE mission. Astrophys. J. Suppl. 140, 81. Lemoine, M., et al., 1999. Deuterium abundances. New Astron. 4, 231. Lemoine, M., et al., 2002. Deuterium abundance toward G191-B2B: results from the FUSE mission. Astrophys. J. Suppl. 140, 67. Linsky, J.L., 1998. Deuterium abundance in the local ISM and possible spatial variations. Space Sci. Rev. 84, 285. Meyer, D.M., et al., 1998. The deAnitive abundance of interstellar oxygen. Astrophys. J. 493, 222. Moos, H.W., et al., 2000. Overview of the far ultraviolet spectroscopic explorer mission. Astrophys. J. 538, L1. Moos, H.W., et al., 2002. Abundances of deuterium, oxygen, and nitrogen in the local interstellar medium: overview of Arst results from the FUSE mission. Astrophys. J. Suppl. 140, 3. Oliveira, C., et al. in preparation. SoAa, U.J., Meyer, D.M., 2001. Interstellar abundance standards revisited. Astrophys. J. 554, L221 (Erratum: Astrophys. J. 558, L147). Sonneborn, G., et al., 2002. Interstellar deuterium, nitrogen, and oxygen abundances toward BD+28◦ 4211: Arst results from the FUSE mission. Astrophys. J. Suppl. 140, 51. Timmes, F.X., Truran, J.W., Lauroesch, J.T., York, D.G., 1997. Light-element abundances from z = 0 to z = 5. Astrophys. J. 476, 464. Wood, B.E., et al., 2002. Deuterium abundance toward WD 1634 − 573: results from the FUSE mission. Astrophys. J. Suppl. 140, 91.