interstellar absorption‐line evidence for high‐velocity expanding structures in the carina...

Interstellar Absorption‐Line Evidence for High‐Velocity Expanding Structures in the CarinaNebula ForegroundAuthor(s): Nolan R. Walborn, Nathan Smith, Ian D. Howarth, Gladys Vieira Kober,Theodore R. Gull, and Jon A. MorseSource: Publications of the Astronomical Society of the Pacific, Vol. 119, No. 852 (February2007), pp. 156-169Published by: The University of Chicago Press on behalf of the Astronomical Society of the PacificStable URL: http://www.jstor.org/stable/10.1086/511756 .

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156

Publications of the Astronomical Society of the Pacific, 119: 156–169, 2007 February� 2007. The Astronomical Society of the Pacific. All rights reserved. Printed in U.S.A.

Interstellar Absorption-Line Evidence for High-Velocity Expanding Structures in theCarina Nebula Foreground

Nolan R. Walborn

Space Telescope Science Institute,1 Baltimore, MD; [email protected]

Nathan Smith2

Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO; [email protected]

Ian D. Howarth

Department of Physics and Astronomy, University College London, London, UK; [email protected].

Gladys Vieira Kober3 and Theodore R. Gull

Laboratory for Extraterrestial Planets and Stellar Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD;[email protected], [email protected]

andJon A. Morse4

Department of Physics and Astronomy, Arizona State University, Tempe, AZ; [email protected]

Received 2006 February 14; accepted 2006 December 11; published 2007 February 2

ABSTRACT. The extreme, high-velocity interstellar absorption-line profiles toward h Carinae and 16neighboring stars in Trumpler 16 are examined, including several new sight lines observed in the ultraviolet withthe Hubble Space Telescope or in the optical from the Magellan and European Southern Observatories. No twosight lines are identical, but many velocity components are in common. When the velocity scale is shifted to astandard of rest defined by the Carina Nebula emission lines, the symmetries between negative and positivevelocities are striking; at least 15 distinct “shells” can be recognized. This circumstance suggests that the complexexpanding structures are predominantly in front of the ionizing cluster. There may be a relationship to indicationsof a supernova remnant in this direction, including a recent Chandra X-Ray Observatory image. Interpretationsin terms of high-energy phenomena generated by ongoing star formation possibly on the near side of the giantH ii region are also discussed.

Online material: color figure

1. INTRODUCTION

The remarkable interstellar absorption-line profiles towardionizing stars of the Carina Nebula (NGC 3372) have beeninvestigated with increasingly powerful optical and ultravioletinstruments for over 30 years (Walborn et al. 2002 and ref-erences therein), but a definitive explanation of their originremains elusive. Indeed, these profiles are more similar to cer-tain quasi-stellar object (QSO) narrow-line, low-ionization sys-tems than to other Galactic sight lines, combining completelyblack troughs at absolute velocities less than about 40 km s�1

1 Operated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.

2 Hubble Fellow. Current address: Astronomy Department, University ofCalifornia, Berkeley, CA.

3 Also with Science Systems and Applications, Inc., Lanham, MD.4 Current address: Observational Cosmology Laboratory, NASA Goddard

Space Flight Center, Greenbelt, MD.

with strong discrete components at higher velocities, in thedominant ultraviolet species (C ii, O i, Mg ii, Al ii, Si ii,Fe ii) (Danks et al. 2001). As many as 26 distinct velocitycomponents have been resolved in single sight lines, over atotal velocity range of 600 km s�1. While some componentsare in common among different stars, the profiles change dras-tically over small angular distances, and no two are identical.Secular variations have been observed in one sight line (Dankset al. 2001).

While no coherent model of this phenomenon has yetemerged, several characteristics suggested a close relationshipto the ionizing stars, namely, its concentration toward the centerof the nebula, the uniqueness of the individual profiles, thesecular variations, and an apparent decline in the number ofhigh-velocity components toward lower mass stars (Garcıa &Walborn 2000). In contrast, the dominant component in thehigh-ionization species (He i, C iv, Al iii, Si iv) and excited-



EXPANDING STRUCTURES TOWARD CARINA NEBULA 157

2007 PASP, 119:156–169

state transitions is clearly associated with the shortward com-ponent of the double nebular emission lines and, hence, thenear side of the globally expanding H ii region (Walborn &Hesser 1975; Walborn et al. 1984, 2002). However, the presenceof strong absorption components at high positive velocities inthe low-ionization lines is a problem for the “local” hypothesis;a few cases might be explained by depth effects within thestellar clusters, but they are in fact as ubiquitous and extensiveas the negative velocities.

Recently, observations of several additional interstellar sightlines toward and in the immediate vicinity of h Carinae (i.e.,within the Trumpler 16 cluster) have become available. It istimely to combine these new data with those previously pub-lished, to search for any systematic kinematical relationshipsthat may appear with the finer spatial sampling. Here the evi-dence that the intricate expanding structures may lie primarilyin the (immediate) foreground of the nebula and its ionizingclusters is emphasized and related to suggestions of a supernovaremnant in this direction from radio and X-ray observations.However, that possibility cannot yet be proven, so other origins,particularly related to recent evidence for large-scale, ongoingstar formation in the nebula, are also discussed.

2. NEW DATA

Interstellar observations toward the Carina Nebula have beenmade with a variety of ground-based optical and space-basedultraviolet instruments, which must be kept in mind when theresults are intercompared, because only the highest resolutionUV data reveal the full complexity and extent of the profiles.Previous optical data have been obtained with the Cerro TololoInter-American Observatory (CTIO) 1.5 m coude (R p 2 #

; Walborn & Hesser 1975) and 4 m echelle (410 R p; Walborn 1982) spectrographs, and with the Liege4[3–6] # 10

echelle spectrograph at the 2 m CASLEO telescope (R p; Garcıa & Walborn 2000) in Argentina. Ultraviolet41.3 # 10

data are from the International Ultraviolet Explorer (IUE)echelles ( ; Walborn & Hesser 1982) and4R p [1–1.5] # 10the Hubble Space Telescope (HST) Space Telescope ImagingSpectrogaph (STIS) high-resolution echelles ( ;5R p 1.1 # 10Walborn et al. 2002). The UV data show many high-velocitycomponents that are not seen in the weaker optical lines, andthe STIS data supersede the IUE for the four stars observedwith the former, resolving all IUE components into multiplesubcomponents. The new data presented here are discussed inthe following subsections. All stars referenced in this paper areidentified in Figure 1.

2.1. HST Space Telescope Imaging Spectrograph

As part of the HST investigations of h Carinae, observationswith the STIS E230H near-ultraviolet (NUV), high-resolutionechelle were made at several epochs. These data reveal intricatestructure and large temporal variations in the ejected circum-stellar shells (Gull et al. 2005). However, complex interstellar

profiles are easily distinguished in these data and are similarto those observed with the same instrumental configurationtoward neighboring O stars by Walborn et al. (2002). Hence,the sight line toward h Car itself can be added to the interstellardata set. The data quality, reduction, and analysis are as describedin the earlier work, with the differences that a less extensivewavelength range was observed, and the “continuum” in thepeculiar h Car spectrum is essentially impossible to define ac-curately. These effects reduce the accuracy of the profile fitting,because most of the weaker lines used to determine the lowervelocity structure (completely black in the strong lines) are notavailable, and meaningful equivalent-width measurements arenot possible. However, the high-velocity measurements, of mostinterest here, have accuracy comparable to that of the previouswork. The interstellar profiles are best defined at the epochs inwhich the circumstellar absorption is weakest; accordingly, theobservations used here are from 2001 October 1 (Mg, Fe;0.2� # 0.09� aperture; ID 9242, PI: A. Danks) and 2002 July4 (Mn; 0.2� # 0.2� aperture; ID 9337, PI: K. Davidson). All ofthe useful profiles for our purpose are shown in Figure 2.

2.2. HST Goddard High Resolution Spectrograph

GHRS observations of HD 93204 were obtained on 1991April 8 in calibration program ID 3146 (PI: D. Ebbets); theinterstellar Si ii l1526 profile in this spectrum was suggestedby N. R. W. to R. Gilliland for a comparison of the three GHRSresolutions. Thus, these data are hardly new, but they have notbeen previously discussed scientifically; since it was not pos-sible to observe HD 93204 with STIS, they are currently uniquefor the present purpose. The GHRS ECH-A echelle had a some-what lower resolution than the STIS high-resolution echelles(i.e., ), but the one-dimensional Digicon detector4R p 8 # 10limited its wavelength coverage to a few A per exposure. Thisobservation occurred before correction of the HST sphericalaberration, but the 0.25� aperture was used, so the spectralresolution was not degraded. The continuum signal-to-noiseratio (S/N) of this observation is only 10 per 2 pixel resolutionelement, so it has been smoothed by 5 pixels for measurementand display. The profile was fitted with the same techniquesused for the STIS data; the availability of only a single UVprofile obviously limits the resolution of blends and realityassessment of weak features, but the prior optical data havebeen used as guides for the fitting, and only well-defined com-ponents are retained for discussion, so the results are reliablefor the present purpose. The profile is shown in Fig-ure 3, together with the STIS data (smoothed by 3 pixels) forthe same line in HD 93205 (which is only 20� or 0.25 pc inprojection from HD 93204) and CPD �59 2603 for comparison(Walborn et al. 2002).

2.3. Magellan Observatory MIKE

The spectra of four relatively faint stars immediately north-east of h Car have been observed in the optical to determine



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Fig. 1.—Identification of all stars discussed, in a CTIO 4 m/MOSAIC2 [O iii] l5007 image of Trumpler 16 in the northern Carina Nebula (see Smith et al.2005a). A six-digit number is from the HDE, five-digit numbers are from the HD, four-digits from the �59� zone of the CPD, and two-digits preceded by “F”from Feinstein et al. (1973). The extended image of the h Car Homunculus is marked with the superimposed Greek letter.

whether they are behind or in front of the ejected nebulosities(Smith & Morse 2004 and references therein), as well as therecently recognized [O iii] “veil” (Smith et al. 2005a); theyappear to be involved, so if they were behind, their spectrashould provide valuable absorption diagnostics of the circum-stellar shells. These stars are Feinstein et al. (1973) Nos. 64,65, 66, and 77. They were observed by N. S. and J. A. M. on2005 February 22 with the Magellan Inamori Kyocera Echelle(MIKE; Bernstein et al. 2003) at the Clay Telescope of the

Magellan Observatory.5 MIKE is a cross-dispersed echellespectrograph that records blue and red channels simultaneously.The blue channel, which covers 3200–5000 A, is equippedwith a 2k # 4k CCD detector. In the spatial direction, pixelswere binned by 2, and the slit width was 0.5�, resulting in a

5 The Magellan Observatory is a joint facility of the Carnegie Observatories,Harvard University, the Massachusetts Institute of Technology, the Universityof Arizona, and the University of Michigan.




2007 PASP, 119:156–169

Fig. 2.—STIS E230H interstellar profiles in the spectrum of h Car. As explained in the text, in this and subsequent figures, the velocity scale at bottomand individual component velocities at top are heliocentric plus 14 km s�1. The notation “cs” identifies circumstellar features at �146 km s�1 heliocentric(Gull et al. 2005).



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Fig. 3.—Profiles of interstellar Si ii l1526 observed with GHRS toward HD 93204 (top) and with STIS toward HD 93205 (center) and CPD �59 2603 (bottom).

pixel scale of A (at 3933 A), and an effective′′0.28 # 0.183spectral resolution of ∼0.068 A ( ). The red chan-4R � 6 # 10nel covers 4900–10000 A with an identical 2k # 4k CCD,and it uses the same slit width, since the red and blue obser-vations are obtained simultaneously. At red wavelengths, how-ever, the pixels were not binned in the spatial direction, and

the plate scale is slightly different, resulting in a pixel scale ofA at the Na i lines. The effective spectral res-′′0.13 # 0.0437

olution measured from the FWHM of emission lines in theThAr lamp is 0.11 A ( ). During the observa-4R � 5.5 # 10tions, the weather was nonphotometric and the seeing was0.8�–1�. The data were not flux-calibrated in view of the sky




2007 PASP, 119:156–169

conditions, but wavelength calibration was performed with theinternal ThAr lamp. Radial velocities of the interstellar com-ponents were measured by cursor settings in screen displaysof the profiles; their accuracy is about 1 km s�1. Despite thevery small angular separations, the spectra of these stars alsohave diverse interstellar profiles with high-velocity compo-nents, as shown in Figures 4 and 5. Detailed component pa-rameters from modeling of these new data are given in theAppendix.

2.4. European Southern Observatory VLT/UVES

For comparison with the very nearby sight lines discussedin § 2.3, we also show in Figures 4 and 5 optical interstellarobservations of h Car itself. These data are from the Ultravioletand Visual Echelle Spectrograph (UVES) at the Very LargeTelescope (VLT) of the European Southern Observatory (ESO)and are as described by Weis et al. (2005). Their resolvingpower is in the blue and in the red. The4 58 # 10 1.1 # 10observations shown were obtained on 2005 February 12.

3. RESULTS

The Carina Nebula emission lines are double, with helio-centric radial velocities of �32 and �4 km s�1 at the positionof HD 93204 (Walborn & Hesser 1975). A global expansionof the giant H ii region at �18 km s�1 about a Carina Nebulastandard of rest (CNSR) at �14 km s�1 heliocentric is implied.Walborn et al. (2002) showed that correcting the interstellarcomponent velocities by �14 km s�1 produces a symmetricaldistribution of depletion effects as a function of radial velocityabout zero. Hence, in order to search for kinematical rela-tionships among the interstellar components, we have cor-rected all radial velocities discussed here (excepting the Ap-pendix) by that amount, including the scales and componentsin Figures 2–6.

A summary listing of high-velocity interstellar components(i.e., with CNSR absolute radial velocities greater than 30 kms�1) toward 17 stars in Trumpler 16 is given in Table 1. Asspecified in the first column, they have been grouped into 15“shells” with approximately symmetrical negative and positivevelocities. Clearly, there is some arbitrariness in these group-ings. A histogram of the velocities is given in Figure 6; itshows that some of the groupings are well peaked and distinctfrom their neighbors, while others are less well defined. (Fivecomponents, at �44, �161, �179, �182, and �202 km s�1,have not been assigned to any grouping.) The poor definitionof the highest velocity groupings, above 140 km s�1, is likelyan observational effect, since the highest velocities are pref-erentially detected only in the subset of stars with high-reso-lution UV data, so they are less numerous. Another observa-tional effect is that only stars with STIS or GHRS data showpositive velocities in shell 1, because of blending with thestrong Galactic disk line-of-sight component—for which, ofcourse, the CNSR correction is not meaningful. No evidence

for systematic projection effects across the field could bediscerned, although in principle some component radial ve-locities could be projections of higher ones in other sightlines. Thus, we do not claim that all of these “shells” areproven physical structures. Nevertheless, these groupingsserve to demonstrate the multiple symmetries between neg-ative and positive velocities among these interstellar profiles.Mean velocities, standard deviations of the means, and num-bers of components (total, negative, and positive) of the 15groupings are listed in Table 2.

Optical observations only are available for seven additionalstars in this field, which do not display strong high-velocityinterstellar components: HD 93343 and CPD �59 2595, 2606,2624, 2626, 2635, and 2636 (Figure 1; Walborn 1982; Garcıa& Walborn 20006). All of these are mid- to late-type O starsor early B stars, in contrast to the very early O types of severalstars with high-velocity components; Garcıa & Walborn pointedout that the latter might thus be produced by interactions ofthe more massive stellar winds with immediately surroundinginterstellar/nebular material. However, as already noted, it isimportant to bear in mind that while some high-velocity com-ponents are strong in the optical lines, others that become quitestrong in the UV are entirely undetected in the optical. Thisinhomogeneity of the data strongly limits any search for ki-nematical systematics over the field. Eventually, all accessiblestars in the field must be observed at high resolution in theUV to establish a complete picture of the interstellar structures.

A further curious property of these interstellar profiles is thatalthough the symmetries between negative and positive veloc-ities have been emphasized here, the intensities of the oppositecomponents at a given velocity are usually anticorrelated. Thiseffect is easily seen in Figures 2 and 3, which show severalexamples in both senses; column densities for individual in-terstellar components in the O-star STIS data are given byWalborn et al. (2002). Whether the intensity asymmetries aremerely a quirk or an important clue to the origin of the phe-nomenon remains to be seen.

Finally, we comment further on the interstellar spectra of theFeinstein stars very near h Car, shown in Figures 4 and 5. Aprimary motivation for these observations was to search forevidence that they lie in front of or behind the h Car circum-stellar shell; in the latter case, they might provide valuableabsorption diagnostics for the shell. Unfortunately, we are un-able to reach any definitive conclusions, for the following rea-sons. We searched for absorption features in the stellar spectracorresponding to the stronger emission lines of the shell, andalso for Ca ii and Na i features, at velocities out to �1800 kms�1, with null results. The high-velocity interstellar lines that areseen are comparable to those found throughout the Carina Neb-

6 Two minor errors in this paper are corrected here. For CPD �59� 2525 inTables 1 and 4, read CPD �59� 2595. The equivalent width of the �196 kms�1 component of Ca ii K in CPD �59� 2574 (Table 4) should read 0.144;we thank Dr. Beatrız Garcıa for supplying the revised value.



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Fig. 4.—Rectified profiles of interstellar Ca ii l3933 toward h Car and four Feinstein et al. (1973) stars very nearby on the sky (see Fig. 1). An overplot ofthe five profiles is shown at the bottom. The broad feature near �130 km s�1 in h Car is circumstellar.




2007 PASP, 119:156–169

Fig. 5.—Rectified profiles of interstellar Na i l5896 toward h Car and four Feinstein et al. (1973) stars very nearby on the sky (see Fig. 1). An overplot ofthe five profiles is shown at the bottom; note that the “high-velocity” features in the Feinstein stars are actually telluric absorptions, as shown by their identity inthe overplot. The broad feature near �130 km s�1 in h Car is circumstellar.



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TABLE 1High-Velocity Interstellar Absorption-Line Components (CNSR, km s�1) toward Stars in Trumpler 16

Shell 93162 2574 93204* 93205* 2600 2603* 2629 h* F64 F65 F66 303308* 2627 F77 2628 2641 2644

15 . . . . . . … … … … … �219 … … … … … … … … … … ….. . . . . . . . … … … … … [�202] … … … … … … … … … … …

14 . . . . . . … [�182] … … … �171 … �170 … [�179] … [�161] … … … … …13 . . . . . . … … �147 … �145 �152 … �148 … … … … … … … … …12 . . . . . . … … … … … �139 … … … … … … … … … … …11 . . . . . . … … … �128 … … … … … … … … �134 … … … …10 . . . . . . … �119 … … … �123 … … … … … �119 … … … … …9 . . . . . . . … … … … … … … �110 … �109 … … … �109 … … …8 . . . . . . . … … �106 … … �106 … … … … … … … … … … …7 . . . . . . . … … … … … … … … … … … �97 … … �94 … �956 . . . . . . . … … �84 �84 �87 �87 … �82 … … … �90 … … Pr? … …5 . . . . . . . … … �76 �75 �77 Pr … … … … … �77 �73 �79 … … …4 . . . . . . . �72 … �68 �69 … … �67 … … … … �68 … … … … …3 . . . . . . . … … … … … �63 … �59 … … … �62/�57 … … … … …2 . . . . . . . �48 … … �52 … �49 … �51 �49 … … �47 … �48 [�44] … …1 . . . . . . . �38 �36 �36 �39 �33 … … �39/�32 �35 �35 �36 �40 … �36 … … …1 . . . . . . . … … 34 32 … 31 … 35 … … … 33 … … … … …2 . . . . . . . … … … 49 … 52 … 56 … … … 49 … … 54 … …3 . . . . . . . … … 63 61 Pr? … 60 … 60 60 … 64 … 59/64 … … …4 . . . . . . . … … 71 … … … … … 68 … … … … … 68 … …5 . . . . . . . … … 79 … … 75 … 77 76 75 … 75 … 74 … … …6 . . . . . . . … … … 83 Pr? (83) … … 89 87 … 85 82 … … … …7 . . . . . . . … … 94 94 … … … 93/100 … … … 97 … … … … …8 . . . . . . . … … Pr 102 104 … … 107 … 104 … 104 … 103 … … …9 . . . . . . . … … 114 114 … 112 … 113 … … … 112 … … … … …10 . . . . . . … … … 122 … 124 … … … … … … … 120 … 124 …11 . . . . . . … … 128 127/132 … 134 … 129 … … … … … … … … …12 . . . . . . … … 137 … 140 141 … … … … … … … … … … …13 . . . . . . … … 151 … 146 … … … … … … … … … … … …14 . . . . . . 174 … … … … … … … … … … … … … … … …15 . . . . . . 214 … … … … … … … … … … … … … … … …

Notes.—The first column gives the shell numbers. Stellar identifications heading subsequent columns are as follows: six digits, HDE; five digits, HD; fourdigits, �59� zone of CPD; two digits preceded by “F,” Feinstein et al. (1973); “h” is h Car. Asterisks denote stars with STIS or GHRS UV data. The notation“Pr” signifies present but not measurable, generally due to blending. Five components in square brackets are isolated and not assigned to any grouping. Thepositive shell 6 velocity in CPD �59 2603 is in parentheses because that component disappeared in a second observation.

ula, and so they cannot be unambiguously identified with the h

Car shell. As already noted, the interstellar spectra of this tightgroup of stars (on the sky; Fig. 1) are remarkably diverse. Twoof them, F65 and F77, show Ca ii lines at �109 km s�1 (withquite different intensities) that are not seen toward the others;however, h Car has a strong feature near that velocity in theultraviolet lines (Fig. 2) that is not detected in its optical spec-trum. This is a specific example of the general problem of datainhomogeneity noted above, which precludes even a conclusionthat some of the Feinstein stars are in front of the material atthat velocity. F65 and F77 also have Ca ii features in com-mon at 74/75 and 103/104 km s�1, but the latter star has oneat �79 km s�1 not seen toward the former, while the formerhas one at 87 km s�1 not present in the latter that is strongtoward F64 (89 km s�1). And F65 has a well-defined featureat �179 km s�1 that is not seen toward any of the other stars,as does F64 at �49 km s�1. Thus, no conclusions regardingthe relative line-of-sight locations of these stars can be drawnfrom this information, except perhaps that F66 is in the fore-ground; clearly, there is intricate interstellar structure across

the line of sight on very small angular scales, as already knownelsewhere in the Carina Nebula (e.g., toward HD 93204 vs.HD 93205; Figs. 1 and 3). The bow shock associated with theshell N condensations is expanding toward these stars (Morseet al. 2001), so it is possible that higher density material movinginto these lines of sight will enable a determination of thedistribution in depth at some future time. A final point of in-terest is the large Na i/Ca ii ratio in the �35 km s�1 componenttoward F64, which is unusual, as can be seen in the figureshere and in Figure 25 of Walborn (1982). The implication isthat it arises in moderately high-velocity material that remainsdepleted. Curiously, the strong feature near that velocity in F66does not share this characteristic, providing yet another ex-ample of the complexity of the interstellar structures. Again,detailed modeling of these profiles is given in the Appendix.

4. DISCUSSION

The first X-ray images of the Carina Nebula from the Ein-stein Observatory provided the surprise that its entire extent is




2007 PASP, 119:156–169

Fig. 6.—Histogram of interstellar velocity components toward members of Trumpler 16 in the Carina Nebula, distinguishing positive and negative velocities.Consecutive groupings are denoted by alternating black and white (except that isolated components at �44, �161, �179, �182, and �202 km s�1 are not assignedto any grouping), and “shell” numbers are indicated above.

TABLE 2Mean CNSR Absolute Radial Velocities of

Shells toward Trumpler 16

ShellMean

(km s�1)j(mean)(km s�1) n n� n�

1 35 0.6 17 12 52 50 0.8 12 7 53 61 0.6 12 4 84 69 0.6 8 5 35 76 0.5 13 6 76 85 0.8 12 6 67 96 0.8 8 3 58 104 0.6 8 2 69 112 0.7 8 3 510 122 0.8 7 3 411 130 1.1 7 2 512 139 0.8 4 1 313 148 1.1 6 4 214 172 1.2 3 2 115 216 2.5 2 1 1Total: … … 127 61 66

a source of diffuse, soft X-rays (Seward et al. 1979; Seward& Chlebowski 1982). Walborn & Hesser (1982) showed thatthe X-ray and high-velocity interstellar energies are compa-rable, while Walborn (1982) showed that in principle, the cu-mulative effects of the known stellar winds in the region aresufficient to drive both high-energy phenomena (see also Smith2006). This result, together with the small angular scale of theinterstellar profile spatial variations, the apparent stellar-massdependence of the complex profiles (Garcıa & Walborn 2000),and the temporal variations found by Danks et al. (2001), en-couraged interpretation of the high-velocity material as beingassociated with and driven by individual massive stars in theionizing cluster of the nebula.

However, the apparent persistence of certain interstellar ve-locity components over the entire field, and especially the ubiq-uity of positive-velocity absorption components, which shouldnot be observed toward the driving sources themselves, couldbe indicative of a global structure predominantly in the fore-

ground of the stellar cluster. Two possible origins of such struc-ture(s) are discussed here.

4.1. A Supernova Remnant toward the Carina Nebula?

Jones (1973) reported low-frequency radio evidence for anonthermal absorption source toward the northeastern sectorof the Carina Nebula, which he interpreted as a supernovaremnant (SNR) in front of the nebula. (Elliott [1979] suggestedthat broad Ha emission near h Car might be related, but thatwas subsequently shown by Boumis et al. [1998 and referencestherein] to be the reflected stellar profile.) More recently, Town-sley et al. (2005) have presented Chandra X-Ray Observatoryresults that rejuvenate the idea of an SNR in this direction.Two discrete, diffuse structures are present in the image: acircular, soft region south of Trumpler 14 and west of Trumpler16, adjacent to the western dark lane, that is not obviouslyrelated to either cluster; and a very high surface brightnessfeature further to the south, seen in an off-axis detector (seealso the discussion of diffuse emission by Evans et al. 2003).For this latter structure, there is spectral evidence of an en-hanced metal content, leading Townsley et al. to propose thatit is an SNR. The full extent of this feature is currently un-known, leaving open the possibility that it may be large (orpart of a larger structure), perhaps related to the earlier radioobservation and the high-velocity interstellar lines.

Three characteristics of the latter are especially relevant inthis context. (1) Several high-velocity profiles are known inthe southern part of the Carina Nebula, toward members of theionizing cluster Collinder 228 there, not otherwise discussedhere; indeed, the highest known interstellar velocity in the neb-ula occurs in the spectrum of HD 93222 in Cr 228 (�388 kms�1; Walborn et al. 2002). Thus, available information is con-sistent with an overall extent of the high-velocity interstellarmaterial that is much greater than the field of Tr 16, which isthe primary focus of this paper because of its current higherdensity of observed sight lines. The lack of “closure” of thevelocities toward the edges of the Tr 16 field, as expected for



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2007 PASP, 119:156–169

a fully covered expanding structure, should also be recalled.(2) The interstellar high-ionization C iv/Si iv ratios of somehigh-velocity components (as opposed to that of the dominant,expanding H ii region component) are consistent with X-rayor collisional ionization (Walborn et al. 1984, 2002). (3) An-other nearby Galactic region with complex, high-velocity in-terstellar profiles is the Vela SNR (Cha & Sembach 2000 andreferences therein).

Shull & Hippelein (1991) developed techniques for derivingthe three-dimensional structure of an SNR from spatially re-solved radial and tangential velocity information. While itmight become possible to attempt a related analysis of theCarina Nebula interstellar velocities in the future, the sheercomplexity of the profiles, the lack of tangential information,the inhomogeneity of the current radial data, and the absenceof velocity closure at the peripheries of the observed fieldsdiscourage such an effort at the present time. In addition tofurther interstellar observations, it will be important to extendthe X-ray observations of the region to pursue the SNRhypothesis.

4.2. Ongoing Star Formation in the Carina Nebula

There is relatively recent and increasingly detailed evidencefor ongoing star formation in the Carina Nebula. In the south-ern part of the nebula, giant pillars, embedded clusters, anda parsec-scale Herbig-Haro flow (HH 666, “the Axis of Evil”)have been recognized (Smith et al. 2000, 2004a, 2005b; Rath-borne et al. 2004). In particular, HH 666 displays velocitiesof �250 km s�1, the same range as the interstellar lines. Indeed,one Cr 228 member with very high velocity components, HD93130 (Walborn 1982; Walborn & Hesser 1982), lies very nearHH 666 on the sky. If there are other as yet undetected pro-tostellar outflows associated with the Carina Nebula, theywould provide a source of material at discrete high velocities.

It is well known that triggered, second-generation star for-mation occurs at the peripheries of giant H ii regions (e.g.,Walborn 2002). In fact, much of the current star formation inthe Carina Nebula occurs on its near side, since dust pillarsand other dark clouds are seen in silhouette against the H iiregion. Protostellar outflows with different velocities and pro-jections on the near side would produce differing high positiveas well as negative velocity interstellar components towardmembers of the first-generation clusters inside. These objectscan be difficult to discern in such complex fields, and existingdata do not provide the detail required for an exhaustive census

at the distance of the Carina Nebula, so others may well remainto be found there.

The requisite level of detail can be seen in the Orion Nebula,the nearest H ii region, and its characteristics are illustrative.In a large HST Ha imaging survey of Orion, Bally et al. (2006)find thin shock structures tracing HH jet outflows and windinteractions throughout, covering a significant fraction of theobserved area. These structures are produced by very youngstars within the nebula, as well as by embedded IR sourceslaunching jets that break out of the background cloud into thenebula (Smith et al. 2004b). In fact, bow shocks around youngstars that point inward toward the center of the nebula trace alarge-scale flow of material, indicating that a majority of theinterior volume is moving supersonically (Bally et al. 2006).These thin shocks will also be more difficult to detect at thelarger distance of the Carina Nebula, but similar HST narrow-band images there do show numerous large-scale shock featuresthroughout, down to the resolution limit (N. Smith et al. 2007,in preparation).

Moreover, a more general interaction between the first-gen-eration stellar winds and second-generation photoevaporativeflows could produce some high interstellar velocities, but maybe more relevant as a source of the large-scale, diffuse soft X-rays. The dust pillars are being irradiated by UV light thatgenerates slow, dense photoevaporative flows from their sur-faces, which diffuse into the H ii region. Simultaneously, thereare fast, hot, low-density accumulated stellar winds flowingfrom Tr 14, Tr 16, and Cr 228. At some point, these two flowswill collide and produce a shock interface, which will have avery complex geometry because of the irregular spatial distri-bution of the photoevaporating pillars. This mechanism maybe relevant to the high-ionization interstellar lines and, hence,their observed profile differences from the low-ionization ones,i.e., the line widths (greater in the former), dominant negative-velocity component, and diverse relative intensities (Walbornet al. 2002).

Further observational and theoretical work will be requiredto establish which if any of these morphological ideas willultimately explain the high-energy phenomena toward the Ca-rina Nebula.

We thank Kerstin Weis for permission to use her VLT ob-servations of h Car. Publication support was provided, andN. S. was supported, by NASA through grants GO-10205.01-Aand HF-01166.01-A, respectively, from the Space Telescope Sci-ence Institute, which is operated by AURA, Inc., under contractNAS 5-26555.




2007 PASP, 119:156–169

TABLE 3Model Fits to Magellan Data

Ca H and K Na D

v,

(km s�1)b

(km s�1)log N

(dex cm�2)v,

(km s�1)b

(km s�1)log N

(dex cm�2)

F64

�59.8 � 0.2 6.1 � 0.3 11.94 � 0.01 … … …�46.0 � 0.5 3.4 � 0.7 11.75 � 0.08 �47.6 � 0.2 2.1 � 0.3 12.09 � 0.05�34.4 � 8.4 4.9 � 6.6 11.9 � 1.0 �34.6 � 1.1 3.9 � 1.8 11.42 � 0.17�30.1 � 1.0 2.3 � 3.8 11.7 � 1.4 … … …�19.9 � 1.2 5.2 � 1.5 12.56 � 0.14 �16.9 � 0.7 9.8 � 1.0 12.53 � 0.05�12.3 � 0.6 3.2 � 0.7 12.56 � 0.13 �13.6 � 1.2 0.2 � 1.4 13.1�1.7 � 0.4 4.5 � 0.9 12.28 � 0.08 … … …�9.5 � 0.2 5.6 � 0.3 12.83 � 0.02 �5.2 � 0.3 6.3 � 0.3 12.86 � 0.04

�23.7 � 0.3 3.9 � 0.5 11.60 � 0.04 … … …�60.0 � 0.7 8.2 � 1.2 11.28 � 0.04 … … …�77.0 � 0.2 0.2 � 0.3 12.0 � 2.0 … … …�82.0 � 0.5 6.5 � 0.6 11.62 � 0.03 … … …

F65

�118.6 � 0.4 3.4 � 0.8 11.26 � 0.05 … … …�43.4 � 4.2 9.2 � 3.6 11.58 � 0.24 �47.6 � 2.3 5.0 � 3.9 11.11 � 0.21�31.4 � 1.2 5.1 � 1.3 12.28 � 0.16 �34.8 � 1.3 3.9 � 2.7 11.53 � 0.19�22.4 � 0.8 4.1 � 1.7 12.43 � 0.22 �23.3 � 0.4 4.6 � 0.8 12.33 � 0.04�12.8 � 1.0 5.6 � 2.5 12.49 � 0.18 … … …�2.1 � 0.5 3.5 � 1.3 12.23 � 0.16 �5.3 � 7.1 7.8 � 5.9 12.2 � 0.6�8.9 � 0.3 5.6 � 0.4 12.90 � 0.02 �5.4 � 2.0 6.6 � 1.0 12.61 � 0.22

�23.5 � 0.5 3.8 � 0.7 11.60 � 0.05 … … …�52.5 � 1.8 3.4 � 3.6 10.65 � 0.21 … … …�63.7 � 0.4 2.5 � 0.9 11.40 � 0.07 … … …�75.4 � 0.8 7.1 � 1.3 11.54 � 0.06 … … …�93.3 � 0.3 1.8 � 0.8 11.25 � 0.04 … … …

F66

�45.8 � 0.6 9.2 � 0.7 12.21 � 0.03 �51.0 � 0.5 3.9 � 1.0 11.46 � 0.06�33.5 � 1.7 2.4 � 1.6 12.00 � 0.44 �31.4 � 0.7 7.1 � 1.1 12.02 � 0.05�27.1 � 2.6 4.1 � 6.9 12.0 � 0.9 … … …�15.1 � 1.2 8.9 � 3.2 12.81 � 0.14 �19.4 � 0.5 2.9 � 0.9 12.03 � 0.07�1.6 � 0.5 3.6 � 1.3 12.37 � 0.15 �7.2 � 2.1 6.2 � 3.1 12.13 � 0.25�9.5 � 0.3 4.7 � 0.5 12.86 � 0.03 �5.0 � 1.2 7.1 � 0.8 12.58 � 0.08

�22.3 � 0.8 4.3 � 1.1 11.66 � 0.08 … … …

F77

�120.9 � 0.5 8.3 � 0.8 11.72 � 0.04 … … …�119.2 � 0.3 1.0 � 1.0 11.43 � 0.08 … … …�88.6 � 0.5 1.5 � 1.4 10.99 � 0.06 … … …

�57.8 1.5 10.48 � 0.18 … … …�47.4 � 0.6 1.8 � 1.6 11.06 � 0.15 �47.6 2.1 7.75

�29.4 8.5 12.2 �30.2 � 0.3 4.4 � 0.5 12.41 � 0.05�25.6 � 4.9 6.1 12.0 �23.8 27.1 11.97 � 0.73�15.2 � 1.5 6.3 � 1.6 12.74 � 0.19 �18.5 � 0.3 2.8 � 0.5 12.52 � 0.09�1.7 � 0.4 4.4 � 0.9 12.37 � 0.08 �2.5 11.1 12.38 � 0.68�9.9 � 0.2 5.3 � 0.3 12.88 � 0.02 �6.9 � 0.6 5.6 � 1.9 12.64 � 0.32

�23.8 � 0.4 3.4 � 0.7 11.53 � 0.05 �13.5 � 7.6 3.4 10.62�52.6 � 0.5 2.9 � 1.1 11.11 � 0.07 … … …�64.3 � 0.2 4.2 � 0.3 11.78 � 0.02 … … …�93.1 � 0.2 3.2 � 0.3 11.61 � 0.02 … … …

�108.0 � 0.6 3.8 � 1.0 11.12 � 0.06 … … …



168 WALBORN ET AL.

2007 PASP, 119:156–169

Fig. 7.—Model fits (gray curve) to the interstellar Ca ii K profiles in the Feinstein stars. [See the electronic edition of PASP for a color version of this figure.]

APPENDIX A

Interstellar-cloud models were fitted to the interstellarprofiles of the Feinstein stars by means of VAPID (Howarth2002), under the customary assumption of a Gaussian line-of-sight velocity dispersion in each “cloud.” With this assumption,each cloud is fully specified by a central radial velocity ,vvelocity-dispersion parameter b, and column density N. (Notethat unlike in the body of the paper, all radial velocities givenin this Appendix are heliocentric.) We optimized theseparameters through least-squares fitting of the model to bothdoublet components simultaneously (allowing for a zero-pointvelocity offset between spectral regions), using atomic data

from Morton (2003). The adopted fits are satisfactory in thatthey provide a reasonable representation of the data (in a formalstatistical sense, as well as judged by eye), but the solutionsfor the low-velocity blends are not unique; that applies to mostof the Na i components, and in the worst cases, the uncertaintiesare unconstrained. The parameters for the high-velocitycomponents are quite secure, however. The results are givenin Table 3, and the Ca ii K fits are illustrated in Figure 7. TheF64 component with an anomalously large Na i/Ca ii column-density ratio occurs at �46/48 km s�1 heliocentric.

REFERENCES

Bally, J., Licht, D., Smith, N., & Walawender, J. 2006, AJ, 131, 473Bernstein, R., Shectman, S. A., Gunnels, S. M., Mochnacki, S., &

Athey, A. E. 2003, Proc. SPIE, 4841, 1694Boumis, P., Meaburn, J., Bryce, M., & Lopez, J. A. 1998, MNRAS,

294, 61Cha, A. N., & Sembach, K. R. 2000, ApJS, 126, 399Danks, A. C., Walborn, N. R., Vieira, G., Landsman, W. B., Gales,

J., & Garcıa, B. 2001, ApJ, 547, L155Elliott, K. H. 1979, MNRAS, 186, 9PEvans, N. R., et al. 2003, ApJ, 589, 509Feinstein, A., Marraco, H. G., & Muzzio, J. C. 1973, A&AS, 12, 331Garcıa, B., & Walborn, N. R. 2000, PASP, 112, 1549

Gull, T. R., Vieira, G., Bruhweiler, F., Nielsen, K. E., Verner, E., &Danks, A. 2005, ApJ, 620, 442

Howarth, I. D. 2002, MNRAS, 335, 267Jones, B. B. 1973, Australian J. Phys., 26, 545Morse, J. A., Kellogg, J. R., Bally, J., Davidson, K., Balick, B., &

Ebbets, D. 2001, ApJ, 548, L207Morton, D. C. 2003, ApJS, 149, 205Rathborne, J. M., Brooks, K. J., Burton, M. G., Cohen, M., & Bon-

temps, S. 2004, A&A, 418, 563Seward, F. D., & Chlebowski, T. 1982, ApJ, 256, 530Seward, F. D., et al. 1979, ApJ, 234, L55Shull, P., Jr., & Hippelein, H. 1991, ApJ, 383, 714




2007 PASP, 119:156–169

Smith, N. 2006, MNRAS, 367, 763 (erratum 368, 1983)Smith, N., Bally, J., & Brooks, K. J. 2004a, AJ, 127, 2793Smith, N., Bally, J., Shuping, R. Y., Morris, M., & Hayward, T. L.

2004b, ApJ, 610, L117Smith, N., Egan, M. P., Carey, S., Price, S. D., Morse, J. A., & Price,

P. A. 2000, ApJ, 532, L145Smith, N., & Morse, J. A. 2004, ApJ, 605, 854Smith, N., Morse, J. A., & Bally, J. 2005a, AJ, 130, 1778Smith, N., Stassun, K. G., & Bally, J. 2005b, AJ, 129, 888Townsley, L. K., Broos, P. S., Feigelson, E. D., & Garmire, G. P.

2005, in IAU Symp. 227, Massive Star Birth: A Crossroads ofAstrophysics, ed. R. Cesaroni, M. Felli, E. Churchwell, & C. M.Walmsley (Cambridge: Cambridge Univ. Press), 297

Walborn, N. R. 1982, ApJS, 48, 145———. 2002, in ASP Conf. Ser. 267, Hot Star Workshop III: The

Earliest Stages of Massive Star Birth, ed. P. A. Crowther (SanFrancisco: ASP), 111

Walborn, N. R., Danks, A. C., Vieira, G., & Landsman, W. B. 2002,ApJS, 140, 407

Walborn, N. R., Heckathorn, J. N., & Hesser, J. E. 1984, ApJ, 276,524

Walborn, N. R., & Hesser, J. E. 1975, ApJ, 199, 535———. 1982, ApJ, 252, 156Weis, K., Stahl, O., Bomans, D. J., Davidson, K., Gull, T. R., &

Humphreys, R. M. 2005, AJ, 129, 1694



interstellar absorption‐line evidence for high‐velocity expanding structures in the carina...

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