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«NGC 1333: A Nearby Burst of Star Formation J. Walawender University of Hawaii, Institute for Astronomy, 640 N. Aohoku Pl. Hilo, HI 96720, USA J. ...»

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Handbook of Star Forming Regions Vol. I

Astronomical Society of the Pacific, 2008

Bo Reipurth, ed.

NGC 1333: A Nearby Burst of Star Formation

J. Walawender

University of Hawaii, Institute for Astronomy, 640 N. Aohoku Pl. Hilo, HI

96720, USA

J. Bally

University of Colorado, Center for Astrophysics and Space Astronomy, 389

UCB, Boulder, CO 80309, USA

J. Di Francesco

Herzberg Institute of Astrophysics, National Research Council of Canada,

5071 West Saanich Road, Victoria, BC V9E 2E7, Canada J. Jørgensen Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA K. Getman Department of Astronomy and Astrophysics, Penn State University, 525 Davey Lab, University Park, PA 16802, USA Abstract. NGC 1333 is the currently most active region of star formation in the Perseus molecular cloud. The presence of emission-line stars and Herbig-Haro objects first established NGC 1333 as an active region of star formation. Today, NGC 1333 is one of the best studied extremely young clusters of low to intermediate mass stars. This region is rich in sub-mm cores, embedded YSOs, radio continuum sources, masers, IRAS sources, SiO molecular jets, H2 and HH shocks, molecular outflows, and the lobes of extinct outflows. Dozens of outflows from embedded and young cluster members criss-cross this region. While the complexity and confusion of sources and outows has made it difficult to unravel the relations between various components, NGC 1333 has illuminated the roles of feedback and clustering phenomena in star formation.

1. Overview of NGC 1333 First discovered by Eduard Sch¨ nfeld in 1855, NGC 1333 (Figs. 1 & 2) is a bright o reflection nebula in the western portion of the Perseus molecular cloud. The earliest references to NGC 1333 in research literature are by Edwin Hubble who included NGC 1333 in a catalog of nebulae used to examine the distribution (Hubble 1922a) and stellar content (Hubble 1922b) of Galactic nebulae. The star BD +30◦ 549 illuminates NGC 1333 and was found to be a B8 spectral type (van den Bergh 1966; Racine 1968).

Walawender et al.

Figure 1. A composite of visible wavelength and infrared images of NGC 1333.

Hα, S II, and i′ images are from the Mosaic camera on the Mayall 4 meter telescope at Kitt Peak (from Walawender et al. 2005). The broadband i′ filter is mapped to blue, the Hα image is mapped to green, and the S II image is mapped to orange. The infrared component (mapped to the red channel) is from the Spitzer Space Telescope

4.6 µm image. The Spitzer image is courtesy of the Legacy Program ”From Molecular Cores to Planet Forming Disks” (NASA/JPL-Caltech & c2d Legacy Team). The field is approximately 35′ across and is oriented North up, East left.

The NGC 1333 reflection nebula and its associated dark cloud L1450 (also known as Barnard 205) are located at the northern end of a degree-long, north-south ridge of CO emission in the Perseus region at the west side of a large cavity in the Perseus molecular cloud (Fig. 1 in Sargent 1979; Loren 1976). Work by Herbig & Kameswara Rao (1972), Herbig (1974), and Liu et al. (1981) showed that NGC 1333 contains numerous H-alpha emission line stars. Today, the term NGC 1333 is used to denote the young stellar cluster in addition to the reflection nebula.

NGC 1333 3 Figure 2. Hα image of the NGC 1333 region from Walawender et al. (2005).

Several key objects are labeled.

The molecular mass in the NGC 1333 region is approximately 450 M⊙ (Warin et al. 1996). The molecular cloud surrounding NGC 1333 contains many cavities surrounded by filaments of dense gas which tend to point away from the most active centers of star formation (Lefloch et al. 1998; Quillen et al. 2005). Although there is some correlation with currently active outflows, most cavities are not associated with obvious sources. Quillen et al. (2005) interpreted the radial filaments pointing away from the NGC 1333 cluster as the walls of ancient outflow cavities which are no longer actively driven, and therefore do not contain Herbig-Haro objects, H2 shocks, or molecular outows.

Walsh et al. (2006) found evidence for pervasive infall of molecular gas onto the NGC 1333 region. They found excess redshifted self-absorption in several transitions of HCO+ which is spatially extended over a 0.39 pc2 region. They interpret this signature ˙ as evidence for a global infall rate of M ≈ 10−4 M⊙ yr−1. Currently, the NGC 1333 cluster contains about 150 young stars with a median age of about 106 years and a total Walawender et al.

mass of about 100 M⊙. Averaged over the last million years, the star formation rate in NGC 1333 must have been close to 10−4 M⊙ yr−1 (see also Walsh et al. 2007).

There are several measurements of the distance to NGC 1333. Cernis (1990) suggested a distance of 220 pc to NGC 1333 based on interstellar extinction. Herbig & Jones (1983) adopted a distance of 350 pc to NGC 1333 based on several previous measurements. Recently, Hirota et al. (2007) have determined a distance to NGC 1333 of 235 ± 18 pc based on VLBI parallax measurements of the SVS 131 source. Though this is a measurement of a single stellar source, it is consistent with the photometric measurements of the cluster made by Cernis (1990), therefore we consider it to be the best value currently available, however the reader should be aware that many papers have used and continue to use distance values of 300-350 pc.

NGC 1333 has been the target of numerous studies across the electromagnetic spectrum. In this chapter we summarize the infrared observations (Section 2.) and describe notable observations in the radio (submillimeter through centimeter wavelengths;

Section 3.) including high resolution interferometric observations.

Protostellar outflows may have played a significant role in the evolution of star formation in NGC 1333 and are described in Section 4. Detailed summaries of four notable objects (SVS 13/HH 7IRAS 2, IRAS 4, and HH 12) are given in Section 5. Lastly, NGC 1333 has been the target of several studies using X-rays which are summarized in Section 6.

2. Infrared Photometric Surveys The population of young stellar objects in the NGC 1333 region has been an obvious target for photometric surveys at near- and mid-infrared through far-infrared wavelengths.

2.1. The First Surveys (pre-1990) The NGC 1333 cluster was first mapped at infrared wavelengths, J (1.25 µm), H (1.6 µm), K (2.2 µm), and L (3.5 µm) by Strom et al. (1976), who identified 25 sources, all likely YSOs. Harvey et al. (1984) presented mid/far-infrared (1 µm–100 µm) photometry of a handful of these sources using the NASA Infrared Telescope Facility (IRTF) and Kuiper Airborne Observatory (KAO). They identified two sources with strongly increasing SEDs from near-infrared wavelengths toward 100 µm, indicative of their embeddedness and association with local warm dust condensations (envelopes in the current terminology). Jennings et al. (1987) used data from the Infrared Astronomical Satellite (IRAS) Chopped Photometric Channel to identify nine distinct farinfrared sources at 50 and 100 µm. They showed that in particular two of these sources (IRAS 1 and IRAS 4) were “protostars”, i.e., obscured by their infalling envelope of gas and dust: the latter did not show a peak in maps of dust temperature constructed on the basis of the emission at these two wavelengths, indicating that it was not significantly warmer than the large scale cloud. Jennings et al. (1987) also speculated that There is some confusion regarding the designation of this source as either SVS 13 or SSV 13. It was listed as source number 13 by Strom et al. (1976), which led to the SVS designation. Herbig & Jones (1983), however, chose to use SSV 13 because “the designation SVS has been pre-empted.” Subsequently both SVS and SSV have been used in the literature when referring to this source. We choose to use the SVS designation to match the majority of the literature, however the reader should be aware of the alternate naming convention.

NGC 1333 5 IRAS 4 was binary in nature based on its association with two maser sources, something which has since then been confirmed through higher resolution mid/far-infrared and (sub)millimeter observations (see Sections 3. and 5.3.).

2.2. After 1990; Near/Mid-IR Wavelengths The early surveys suffered from poor resolution, a particular issue in regions such as NGC 1333 where the source density is high. The continued development of nearinfrared ground based detectors allowed for a number of deep ground based surveys of NGC 1333 at near-infrared (J, H, and K) wavelengths up through the 1990s and early 2000s.

Aspin et al. (1994) mapped 10′ ×10′ of the southern region of NGC 1333 using the United Kingdom Infrared Telescope (UKIRT) and identified 134 sources complete down to a K magnitude of 16.0. Cross referencing this list with that of Strom et al.

(1976), they found 13 overlapping sources. Based on near-infrared and optical colorcolor diagrams (specifically J −H vs. H −K), Aspin et al. identified 55 likely pre-main sequence stars from this sample along with another 14 candidates. The remainder of the sample were likely reddened background stars. Of the possible pre-main sequence stars, only a small group (3) showed colors consistent with Class I YSOs, about 25% showed colors and magnitudes consistent with T-Tauri stars and the remainder were consistent with low-mass T-Tauri like pre-main sequence stars with masses 0.2 M⊙.

A subset of this region was surveyed in L-band (3.42 µm) by Aspin & Sandell (1997) confirming the nature of the infrared excess sources and aiding in the classification of some of these candidates.

Lada et al. (1996) covered a somewhat larger region of NGC 1333, also at J, H, K, but slightly shallower (completeness at K of 14.5 magnitudes). They found that the infrared sources in the region were non-uniformly clustered into two groups, one centered around the reflection nebula around BD +30◦ 549 and the other around the southern part of the cluster studied by Aspin et al. (1994). They also found that the bulk of the stars (61%) associated with this “double cluster” showed infrared excesses, indicative of these clusters being young (∼ 106 years) and thereby significantly different from the other prominent cluster in the Perseus region: IC 348 (see chapter by Herbst in this volume). Aspin (2003) performed infrared spectroscopy of a subsample of the sources in the southern cluster. Based on HR diagram classification of these sources and comparison to theoretical evolutionary tracks, it was suggested that the ages of young stars in NGC 1333 covered a wide range from a few×105 years up to sources close to the Zero Age Main Sequence at 5×107 years.

A deep J, H, and K survey (to a K magnitude of 16) of the northern cluster was performed by Wilking et al. (2004). From the near-infrared colors of the objects based on this survey, they identified 25 brown dwarf candidates. These sources were targets for follow-up observations using low resolution near-infrared spectroscopy to spectrally confirm the very low-mass nature of these sources.

Greissl et al. (2007) examined the core of the NGC 1333 cluster using NICMOS on HST and determined the IMF of the cluster to be consistent with a field IMF.

2.3. Spitzer and Beyond As a prelude to the Spitzer observations, Rebull et al. (2003) surveyed a small number of the more embedded objects in N (10.8 µm) and Q (17.9 µm) using the MIRLIN camera on the Palomar 5 m telescope and the NASA IRTF. They detected eight sources Walawender et al.

at these wavelengths and, together with SEDs compiled from the literature, classified them according to their embedded nature.

The NGC 1333 region was surveyed with the Spitzer Space Telescope, under a number of programs including the “Cores to Disks” legacy project (as part of Perseus;

see Jørgensen et al. 2005b and Rebull et al. 2007) and the GTO Spitzer Young Cluster Survey. From these combined data, Gutermuth et al. (2008) found 137 members associated with NGC 1333 itself, 39 protostars and 98 pre-main sequence stars with disks. Class I objects were found to have a spatial distribution similar to that of dense gas found in the region, as traced by Sandell & Knee (2001), while Class II objects accounted for the “double-cluster” morphology seen by Lada et al. (1996). The two density peaks of this morphology are anticorrelated with locations of dense gas. Despite this difference, the nearest-neighbor distance distributions of both classes each peak at 0.045 pc, suggesting the Class II population is both very young and has a low overall velocity distribution. They further argue that the cavities in the center of NGC 1333 were thus dispersed by the Class II populations and not by outflows. Overall, NGC 1333 was revealed to have a roughly uniform density distribution within a 0.3 pc radius, and a steep decline at larger radii, possibly reflecting original cloud structure.

Relative to the IC 348 cluster (also in Perseus but at the opposite end of the cloud), NGC 1333 shows a larger fraction of Class I objects vs. Class II objects, suggesting a significant age difference between these clusters. Indeed, NGC 1333 may be more similar in age to the smaller, very young groups in Perseus, e.g., L1448, L1455, or B1.

Interestingly, before Spitzer, a small fraction of the deeply embedded protostars in the region were known to have mid-infrared counterparts, but the high sensitivity and high angular resolution of the Spitzer observations identified a number of these sources at wavelengths as short as 3.6 µm, making it possible to characterize them.

To establish a relatively unbiased sample of such sources, Jørgensen et al. (2007b) combined surveys by Spitzer and the Submillimetre Common-User Bolometer Array (SCUBA) at the James Clerk Maxwell Telescope (JCMT) and studied the separation between the mid-IR sources and the SCUBA clumps and the characteristics of both (see Fig. 3). About half of the dust condensations in NGC 1333 were found to have associated mid-infrared sources and these cores were forming stars with an efficiency of 10 − 15% (not including the efficiency of forming the cores in the first place), similar to what is observed in the larger scale cloud.

3. Submillimeter, Millimeter & Radio Observations of NGC 1333

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