EDP Sciences
Herschel: the first science highlights
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Issue
A&A
Volume 518, July-August 2010
Herschel: the first science highlights
Article Number L94
Number of page(s) 5
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361/201014612
Published online 16 July 2010
A&A 518, L94 (2010)

Herschel: the first science highlights

LETTER TO THE EDITOR

Hier ist wahrhaftig ein Loch im Himmel[*],[*],[*]

The NGC 1999 dark globule is not a globule

T.  Stanke1 - A. M. Stutz2,3 - J. J. Tobin4 - B. Ali5 - S. T. Megeath6 - O. Krause2 - H. Linz2 - L. Allen7 - E. Bergin4 - N. Calvet4 - J. Di Francesco8,9 - W. J. Fischer6 - E. Furlan10 - L. Hartmann4 - T. Henning2 - P. Manoj11 - S. Maret12 - J. Muzerolle13 - P. C. Myers14 - D. Neufeld15 - M. Osorio16 - K. Pontoppidan17 - C. A. Poteet6 - D. M. Watson11 - T. Wilson1

1 - ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
2 - Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
3 - Department of Astronomy and Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
4 - Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
5 - NASA Herschel Science Center, California Institute of Technology, 770 South Wilson Ave, Pasadena, CA91125, USA
6 - Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA
7 - National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
8 - Department of Physics and Astronomy, University of Victoria, PO Box 355, STN CSC, Victoria BC, V8W 3P6, Canada
9 - National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria BC, V9E 2E7, Canada
10 - JPL, California Institute of Technology, Mail Stop 264767, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
11 - Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627, USA
12 - Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, CNRS, UMR 571, BP 53, 38041 Grenoble, France
13 - Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
14 - Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
15 - Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
16 - Instituto de Astrofisica de Andalucia, CSIC, Camino Bajo de Huetor 50, 18008, Granada, Spain
17 - Division of Geological and Planetary Sciences 150-21, California Institute of Technology, Pasadena, CA 91125, USA

Received 31 March 2010 / Accepted 3 May 2010

Abstract
The NGC 1999 reflection nebula features a dark patch with a size of $\sim$10 000 AU, which has been interpreted as a small, dense foreground globule and possible site of imminent star formation. We present Herschel PACS far-infrared 70 and 160 $\mu $m maps, which reveal a flux deficit at the location of the globule. We estimate the globule mass needed to produce such an absorption feature to be a few tenths to a few  ${M}_{\odot}$. Inspired by this Herschel observation, we obtained APEX LABOCA and SABOCA submillimeter continuum maps, and Magellan PANIC near-infrared images of the region. We do not detect a submillimer source at the location of the Herschel flux decrement; furthermore our observations place an upper limit on the mass of the globule of ${\sim}2.4\times 10^{-2}$  ${M}_{\odot}$. Indeed, the submillimeter maps appear to show a flux depression as well. Furthermore, the near-infrared images detect faint background stars that are less affected by extinction inside the dark patch than in its surroundings. We suggest that the dark patch is in fact a hole or cavity in the material producing the NGC 1999 reflection nebula, excavated by protostellar jets from the V 380 Ori multiple system.

Key words: ISM: clouds - ISM: individual objects: NGC 1999 - ISM: jets and outflows - infrared: ISM - dust, extinction

1 Introduction

In the year 1774 C.E. Friedrich Wilhelm Herschel first noticed patches of sky in the constellation Scorpio that were devoid of stars. Unable to find even the faintest star in these regions, his sister Caroline reported him to exclaim: ``Hier ist wahrhaftig ein Loch im Himmel!'' (``Truly there is a hole in the sky here!''). These dark areas are now known to be due to obscuring material (e.g., Barnard et al. 1927): clouds of molecular gas, whose dust content absorbs the light of background stars. Dark clouds, ranging in mass and size from giant molecular clouds (GMCs) to tiny globules, are the sites of star formation in our Galaxy.

NGC 1999 is a small reflection nebula in the NGC 1999 portion of the Orion A GMC, located in a small group of 22 pre-main sequence stars and protostars, including the driving source of the prototypical Herbig-Haro objects NGC 1999 and NGC 1999 (Megeath et al., in prep.). It is illuminated by the Herbig Ae/Be star NGC 1999, a multiple system with a circumsystem disk where the primary is a 100 $L_{\odot}$ B9 star exhibiting strong emission lines (e.g., Alecian et al. 2009; Hillenbrand et al. 1992; Leinert et al. 1997). NGC 1999 features a compact (20-30 $^{\prime \prime }$) dark patch (see Fig. 1), which is described in the literature as a dark globule and potential site of star formation (e.g., Herbig 1946; Warren-Smith et al. 1980; Herbig 1960), but which has never been studied in greater detail before.

We report here the serendipitous and surprising detection with PACS of a 70 and 160 $\mu $m flux decrement at the location of NGC 1999. The maps show a dark patch against the nebulous far-IR emission that closely resembles the dark patch seen at visible wavelengths. The MSX, ISO, and Spitzer space telescopes have detected clouds in absorption at mid-IR (5-30 $\mu $m) wavelengths against the diffuse IR background of the Galaxy (e.g., Tobin et al. 2010; Stutz et al. 2008,2009a; Bacmann et al. 2000), in a few cases even at 70 $\mu $m (Stutz et al. 2009b). However, the detection of the NGC 1999 globule by PACS would be the first detection of a dark globule in absorption at 160 $\mu $m. At wavelengths $\ge$160 $\mu $m, cold globules are normally detected through the emission from cold (10-30 K) dust. Furthermore, absorption at these wavelengths requires extinctions in excess of 100 AV.

Motivated by the possible discovery of a 160 $\mu $m dark cloud, we obtained follow-up ground based submillimeter and near-IR (extinction) observations towards the globule. We did not detect the column density or mass of cold dust necessary to produce such an absorption feature in the far-IR. We therefore conclude that the dark globule is actually a cavity in the NGC 1999 cloud carved by outflows from the V 380 Ori system. Thus, the Herschel telescope has discovered what truly is a hole in the sky.

\begin{figure}
\par\includegraphics[angle=270,width=8cm,clip]{14612fg1.ps}\vspace{-2mm}
\vspace*{-3mm}
\vspace{-2mm}\end{figure} Figure 1:

NGC 1999 and HH 1/2 region (DSS, left) and HST F450W/F555W/F675W true color image of the NGC 1999 dark patch.

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2 Observations and processing

2.1 Herschel PACS observations

NGC 1999 was observed with Herschel (Pilbratt et al. 2010) with the PACS instrument (Poglitsch et al. 2010) at 70 and 160 $\mu $m on 2009 October 9 (OBSIDs 1342185551 and 1342185552) as part of the science demonstration phase observations of the Herschel Orion Protostar Survey (HOPS; P.I. S. T. Megeath). The data are presented in Figs. 2 and 3 (see also Fischer et al. 2010). They were processed with the Herschel common software system (HCSS[*]) version 3.0 build 919, following standard steps, using v. 4 of the calibration file. After initial processing the two orthogonal scans were combined into a single observation. We used the same HCSS software modules as the automatic PACS pipeline. We used two different approaches for combining the data into final mosaics:

Method 1: Simple (``naive'') mapping with baseline removal. To preserve the extended emission we estimated the sky and the correlated signal drifts observed in PACS readouts (Sauvage et al. 2010). To determine the baselines, we removed pixel-to-pixel electronic offsets using the median of the entire time stream, then calculated the median for each frame/readout. The median values were divided into 500 readout bins, and we took the minimum value for each bin. This approach preserves the extended emission at all spatial scales, but does not remove 1/f noise. The final mosaic was created using the ``photProject'' routine.
Method 2: Optimal mapping with MADmap[*] to remove the bolometer 1/f noise from the pixel time-line. The initial processing is the same as for Method 1. However, instead of 'photProject', MADmap is used to determine an optimal solution for each sky pixel. This method preserves extended emission and removes the 1/f noise, at the price of a reduced sensitivity.

\begin{figure}
\par\includegraphics[angle=270,width=8cm,clip]{14612fg2.eps}\vspace{-2mm}
\vspace{-2mm}
\vspace{-2mm}\end{figure} Figure 2:

NGC 1999/HH 1/2 region as seen with Herschel PACS at 160 $\mu $m (left, the box marks the region shown in Fig. 3), and APEX SABOCA at 350 $\mu $m (right, smoothed to 10 $^{\prime \prime }$ resolution), all displayed with a logarithmic color stretch.

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2.2 Other data

APEX SABOCA and LABOCA - We obtained submillimeter continuum maps using LABOCA and SABOCA on APEX. LABOCA (Siringo et al. 2009) is a $\sim$250 bolometer array operating at 870 $\mu $m, with a spatial resolution of 19 $^{\prime \prime }$. Observations were done on 2009 November 29 and 30 in fair conditions, with precipitable water vapour (PWV) values around 1 mm ( $\tau_{{\rm zenith,} 870} \sim 0.26$). We used a combination of spiral and straight on-the-fly scans in order to recover extended emission. Data reduction was done with the BOA software (Schuller et al., in prep.) following standard procedures, including iterative source modeling. SABOCA (Siringo et al. 2010) is a 37 bolometer array operating at 350 $\mu $m, with a resolution of 7 $.\!\!^{\prime\prime}$8. Data were taken on 2009 December 1st and 3rd (NGC 1999) and on 2008 October 7 and 8 (HH 1/2 area) with PWV < 0.5 mm ( $\tau_{{\rm zenith,} 350} < 1$). The observing and data reduction procedures were similar to those used for LABOCA. The 350 $\mu $m map is presented in Fig. 2, and both maps in Fig. A.1 (available in electronic form only).

Magellan PANIC - NGC 1999 was observed with the PANIC near-IR camera (2$^\prime$ field of view) at Magellan on 2009 December 4 in photometric conditions through H, $K_{\rm s}$ and H2 filters in 0 $.\!\!^{\prime\prime}$3 to 0 $.\!\!^{\prime\prime}$4 seeing. Separate sky exposures were taken for each filter. The data were reduced with standard near-IR routines in the IRAF UPSQIID package. The photometry is presented in Appendix B. The $K_{\rm s}$ and H2 images are shown in Figs. 3 and 4, respectively.

3 Data analysis

3.1 Herschel 70 $\mu $m and 160 $\mu $m

\begin{figure}
\par\includegraphics[width=18.3cm,clip]{14612fg3.eps}\vspace{-1mm}
\vspace*{-2.5mm}
\end{figure} Figure 3:

1 $.\mkern -4mu^\prime $75$\times $1 $.\mkern -4mu^\prime $75 images of the region around NGC 1999 (including V 380 Ori) centered on RA = $5^{\rm h} 36^{\rm m} 24.4^{\rm s}$, Dec = $-06\hbox {$^\circ $ }42\hbox {$^\prime $ }56.4\hbox {$^{\prime \prime }$ }$ (J2000). The white circle ( $14\hbox {$^{\prime \prime }$ }$ diameter) on the PANIC near-IR $K_{\rm s}$ image indicates the NGC 1999 region; the image is annotated with the source designations for five faint stars in the field as listed in Table B.1, where we give their ( $H - K_{\rm s}$) colors. The PACS 70 $\mu $m and 160 $\mu $m maps both show NGC 1999 observed as a flux deficit; the overlays represent the pixel masks used for the analysis of the NGC 1999 feature. The right-most two panels show the SABOCA and LABOCA maps.

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A cursory inspection of the Herschel data (Figs. 2 and 3) immediately reveals a flux decrement in both PACS maps, which closely follows the morphology of the putative dark globule in NGC 1999. Following Stutz et al. (2009b), we determine the column density and mass of the putative globule in the foreground of NGC 1999, assuming that the observed 70 and 160 $\mu $m decrement is due to extinction. The optical depth is given by

\begin{displaymath}\tau = -1.0 \cdot \ln [(f + f_{\rm BG})/(f_0 + f_{\rm BG})],
\end{displaymath} (1)

where f is the shadow flux level, f0 is the intrinsic unabsorbed flux level, and $f_{\rm BG}$ is the background contribution to the flux zero-level in the images. We estimate the shadow flux level f as the mean pixel value in a $\sim$7 $^{\prime \prime }$ radius region centered on the darkest part of NGC 1999; the unobscured flux level f0 is estimated as the median pixel value in a half-annulus with inner and outer radii of 15 $^{\prime \prime }$ and 30 $^{\prime \prime }$, with a southwest orientation chosen to avoid the bright V 380 Ori flux. The fand f0 image regions are over-plotted on the PACS maps in Fig. 3. The $f_{\rm BG}$ flux level is not present in the Herschel maps because constant flux level pedestals are removed by the data reduction. We estimate the 70 $\mu $m BG flux value by interpolating the IRAS 60 and 100 $\mu $m images; the 160 $\mu $m BG flux values were obtained from the ISO Serendipity Survey in the near vicinity of NGC 1999. In both cases we take 50% of the total measured flux as our estimate for $f_{\rm BG}$ as we are only interested in the missing flux originating from behind NGC 1999, and not the foreground component. While this assumption is crude, the $f_{\rm BG}$ values are low compared to the f and f0levels and do not have a large effect on our analysis.

Following Eq. (1), we calculate the mean optical depth per pixel. Table 1 presents the results for the data reduced with both methods (which we find to agree well, indicating that both recover extended emission equally well). From the resulting optical depth we calculate the column density and mass (in a $7\hbox{$^{\prime\prime}$ }$ radius aperture) required to cause this flux-decrement at the two PACS wavelengths; these are presented in Table 1. We use the extreme Ossenkopf & Henning (1994) model dust opacities for grains with thick ice mantles: $\kappa_{70} = 541$ cm2g-1 and $\kappa_{160} =
55.7$ cm2g-1, a gas-to-dust mass-ratio equal to 100, and a distance of 420 pc (e.g., Menten et al. 2007). The resulting column densities and masses for the two wavelength bands are clearly inconsistent. For example, we derive that masses of 0.1  ${M}_{\odot}$ and 2.5  ${M}_{\odot}$ are needed to account for the observed flux decrement in the the 70 and 160 $\mu $m data, respectively.

\begin{figure}
\par\includegraphics[angle=270,width=9cm,clip]{14612fg4.eps}\vspace{-2mm}
\vspace*{-2.5mm}
\end{figure} Figure 4:

Left: PANIC near-IR H2 narrow-band image of the NGC 1999; right: the same image with a scaled $K_{\rm s}$ continuum image subtracted.

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Table 1:   Far-infrared optical depth, mass, and column density estimates.

3.2 Ground-based follow-up

Neither the APEX 350 nor 870 $\mu $m maps show an emission feature at the location of the Herschel flux decrement. Instead, the submillimeter emission bears a strong resemblance to the 160 $\mu $m emission, suggesting that the 160, 350, and 870 $\mu $m maps are all tracing the morphology of the dust emission (Fig. 3). This morphology is suggestive of a diffuse ring of material, not a hot region absorbed by a foreground cold cloud. Assuming optically thin dust emission, total gas+dust masses can be obtained from submillimeter fluxes as

\begin{displaymath}M_{{\rm G}+{\rm D}} =
\frac{M_{\rm G}}{M_{\rm D}} \frac{S_\nu d^2}{B_\nu(T_{\rm D}) \kappa_{\nu, {\rm D}}},
\end{displaymath} (2)

where $\frac{M_{\rm G}}{M_{\rm D}}$ is the gas-to-dust mass ratio, $S_\nu$ the flux density, d the distance, $B_\nu(T_{\rm D})$ the Planck function, and $\kappa_{\nu, {\rm D}}$ the dust opacity.

With an rms noise level of $\sim$13 mJy in our LABOCA map, we should be able to detect (3 $\sigma$) a 40 mJy point source, corresponding to a mass of 0.13  ${M}_{\odot}$, assuming $T_{\rm D}=10$ K and Ossenkopf & Henning (1994) opacities for thick ice mantle grains. Although the 870 $\mu $m sensitivity limits are uncertain due to the surrounding highly structured low surface-brightness emission, we conclude that a mass around 0.1  ${M}_{\odot}$ should have been detected in the LABOCA map. More interestingly, the rms noise on the SABOCA map is around 17 mJy, implying a 3$\sigma$ point-source detection limit of $\sim$50 mJy. Due to the steeply rising Planck function and dust opacity, this limit corresponds to a much lower mass detection limit of only $2.4 \times 10^{-2}$  ${M}_{\odot}$. For comparison, the mass necessary to produce an extinction shadow as derived from the 70 $\mu $m map (on the order of 0.1  ${M}_{\odot}$) would produce a 350 $\mu $m source with a flux of $\sim$200 mJy, i.e., a ${>}10\sigma$detection. This result is in stark contradiction with the dense globule/shadow interpretation of the absorption features observed in the Herschel data.

The PANIC images show five faint stars around V 380 Ori, marked in Fig. 3 with their source designation as listed in Table B.1, where we also give their $(H-K_{\rm s})$ colors and estimated extinction. Stars 3 and 4 are within the dark patch and have moderately red colors, implying a mean extinction of $A_V \sim 10$. In comparison, stars 1, 2, and 5 outside the dark patch are slightly redder and have a mean extinction of $A_V \sim 12$. None of the five stars are apparent in the HST images, indicating that they are background stars (Fig. 1). The $H - K_{\rm s}$ colors show that the extinction toward the dark patch is much less than the 100 AV needed to attenuate the 160 $\mu $m emission and that the extinction through the dark patch is slightly less than that through the surrounding region.

4 Discussion

Optical images of NGC 1999 show a dark patch suggestive of a small, dense globule obscuring the NGC 1999 reflection nebula. Surprisingly, our 70 and 160 $\mu $m images clearly show a dark patch against the bright nebula with a strikingly similar morphology to that in visible light images. These Herschel measurements, combined with subsequent ground based data, lead to the conclusion that the dark feature is a hole in the NGC 1999 nebula. First, we find that the masses needed to cause the 70 and 160 $\mu $m dark patch - 0.1 and 2.5  ${M}_{\odot}$, respectively - are inconsistent. Furthermore, the globule is not detected in emission at 350 and 870 $\mu $m: the SABOCA obervations place an upper limit of $2.4 \times 10^{-2}$  ${M}_{\odot}$ for a temperature of 10 K. This upper limit is far below the amount of mass needed to cause the obscuration in the PACS data. Finally, near-IR observations with PANIC detect background stars toward the dark patch; the $H - K_{\rm s}$ colors of these stars are slightly bluer than stars detected outside the globule, suggesting a lower extinction toward the dark patch. Furthermore, the extinctions of the background stars are less than that required to absorb the 160 $\mu $m flux. Taken together, these observation show that the dark patch is not a globule, but instead a cavity in the nebula.

The presence of a well delineated cavity of the size of $\sim$10 000 AU deserves some attention. With the typical turbulent velocities on the order of a few km s-1 in clouds, such a cavity should be filled on timescales of at most a few 10 000 yrs and quickly disappear. The PANIC H2 narrow band data (Fig. 4) deliver important hints about the possible origin and peculiar

shape of the cavity. They reveal a previously unknown, faint H2 bow shock enveloping the SMZ 60/HH 148 compact knots (Stanke et al. 2002; Corcoran & Ray 1995), constituting the clearest evidence so far for a collimated flow running northeast to southwest through the cavity. This flow, which likely originates in the V 380 Ori multiple system, could possibly excavate the southern part of the cavity. NGC 1999 in the southeastern corner of the PANIC image resembles a small bow shock in a flow coming from the northwest; together with NGC 1999, located northwest of V 380 Ori (Fig. 1), it indicates a second, northwest to southeast oriented flow, which could be responsible for digging the northwestern lobe of the cavity.

We note a similar flux depression in the 160 $\mu $m Herschel image southwest of the protostar HOPS 166, which drives the NGC 1999 outflow (Corcoran & Ray 1995). Optical images (e.g., Fig. 1) show a circular reflection nebula marking the HH 147 outflow cavity, coinciding with the far-IR flux depression. The NGC 1999 dark patch may therefore only be a somewhat peculiar example of a cavity carved in the ambient medium by an outflow, rendered particularly visible by the illumination and heating of the cavity walls by V 380 Ori. Sensitive far-IR maps taken with Herschel may therefore provide a new tool to assess the importance of outflow feedback on cloud cores.

Acknowledgements
We thank Frank Bertoldi and Markus Albrecht for their invaluable help with BOA, Giorgio Siringo for his help with the SABOCA data, Jonathan Williams for encouraging discussions, and the APEX staff for their help wiht taking the data. Based in part on observations made with Herschel, a European Space Agency Cornerstone Mission with significant participation by NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. J.J.T. acknowledges funding through HST-GO-11548.04-A. Figure 1 produced from data taken with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).


References

Online Material

Appendix A: SABOCA and LABOCA submillimeter maps

\begin{figure}
\par\includegraphics[angle=270,width=18cm,clip]{14612fgA1.eps}
\end{figure} Figure A.1:

Full submillimeter maps. Left: SABOCA, displayed at the original resolution of 7 $.\!\!^{\prime\prime}$8; right: LABOCA. Protostars in the field are labeled with their HOPS designations. For both maps a logarithmic color scale is used.

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Appendix B: PANIC H and K $_{\rm\sf s}$ photometry

Table B.1:   PANIC NGC 1999 near-IR colors of background stars.

Five faint stars are visible in the PANIC H and $K_{\rm s}$ images. Their positions and photometry are listed in Table B.1. Photometric calibration was performed with 2MASS[*] photometry of comparison fields containing 20 2MASS sources and verified with a 2MASS star in the science field. Photometry was conducted with the IRAF task apphot.

The measured $(H - K_{\rm S})$ color was used to estimate the extinction AV toward the stars. We assumed an intrinsic $(H - K_{\rm S})$ color of 0.17, derived as the median $(H - K_{\rm S})$ colors of stars in an unreddened control field near Orion (Megeath et al., in prep). We adopted the reddening law of Indebetouw et al. (2005) to convert $(H - K_{\rm S})$ excess into K-band extinction AK, from which we obtained the optical extinction as $A_V = 8 \times A_K$, corresponding to a total to selective extinction RV between the diffuse ISM value of 3.1 and the higher values (up to 5) found for dense clouds (e.g. Campeggio et al. 2007).

Footnotes

... Himmel[*]
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA
...[*]
This publication includes data acquired with the Atacama Pathfinder Experiment (APEX; proposal E-082.F-9807 and E-284.C-5015). APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
...[*]
Appendices A and B are only available in electronic form at http://www.aanda.org
... (HCSS[*]
HCSS is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS, and SPIRE consortia.
... MADmap[*]
Microwave Anisotropy Dataset mapper (Cantalupo et al. 2010, see Poglitsch et al. 2010, for its implementation in HCSS).
... 2MASS[*]
The Two Micron All Sky Survey is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.
Copyright ESO 2010

All Tables

Table 1:   Far-infrared optical depth, mass, and column density estimates.

Table B.1:   PANIC NGC 1999 near-IR colors of background stars.

All Figures

  \begin{figure}
\par\includegraphics[angle=270,width=8cm,clip]{14612fg1.ps}\vspace{-2mm}
\vspace*{-3mm}
\vspace{-2mm}\end{figure} Figure 1:

NGC 1999 and HH 1/2 region (DSS, left) and HST F450W/F555W/F675W true color image of the NGC 1999 dark patch.

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In the text

  \begin{figure}
\par\includegraphics[angle=270,width=8cm,clip]{14612fg2.eps}\vspace{-2mm}
\vspace{-2mm}
\vspace{-2mm}\end{figure} Figure 2:

NGC 1999/HH 1/2 region as seen with Herschel PACS at 160 $\mu $m (left, the box marks the region shown in Fig. 3), and APEX SABOCA at 350 $\mu $m (right, smoothed to 10 $^{\prime \prime }$ resolution), all displayed with a logarithmic color stretch.

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In the text

  \begin{figure}
\par\includegraphics[width=18.3cm,clip]{14612fg3.eps}\vspace{-1mm}
\vspace*{-2.5mm}
\end{figure} Figure 3:

1 $.\mkern -4mu^\prime $75$\times $1 $.\mkern -4mu^\prime $75 images of the region around NGC 1999 (including V 380 Ori) centered on RA = $5^{\rm h} 36^{\rm m} 24.4^{\rm s}$, Dec = $-06\hbox {$^\circ $ }42\hbox {$^\prime $ }56.4\hbox {$^{\prime \prime }$ }$ (J2000). The white circle ( $14\hbox {$^{\prime \prime }$ }$ diameter) on the PANIC near-IR $K_{\rm s}$ image indicates the NGC 1999 region; the image is annotated with the source designations for five faint stars in the field as listed in Table B.1, where we give their ( $H - K_{\rm s}$) colors. The PACS 70 $\mu $m and 160 $\mu $m maps both show NGC 1999 observed as a flux deficit; the overlays represent the pixel masks used for the analysis of the NGC 1999 feature. The right-most two panels show the SABOCA and LABOCA maps.

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In the text

  \begin{figure}
\par\includegraphics[angle=270,width=9cm,clip]{14612fg4.eps}\vspace{-2mm}
\vspace*{-2.5mm}
\end{figure} Figure 4:

Left: PANIC near-IR H2 narrow-band image of the NGC 1999; right: the same image with a scaled $K_{\rm s}$ continuum image subtracted.

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In the text

  \begin{figure}
\par\includegraphics[angle=270,width=18cm,clip]{14612fgA1.eps}
\end{figure} Figure A.1:

Full submillimeter maps. Left: SABOCA, displayed at the original resolution of 7 $.\!\!^{\prime\prime}$8; right: LABOCA. Protostars in the field are labeled with their HOPS designations. For both maps a logarithmic color scale is used.

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In the text


Copyright ESO 2010