# ProtostarsInNGC281

The idea is to start gathering two items:

1. Relevant figures
2. Text and references.

• Carol.

### Introduction to NGC 281

NGC 281 is an active star-forming nebulosity about 2.81± 0.24 kpc or 9200 light-years away at a relatively high galactic latitude ($\displaystyle \alpha$ 2000=00h52m, $\displaystyle \delta$ 2000=+56d34m or l=123.1deg, b= -6.3deg) in the constellation Cassiopeia. It is often referred to as the "PacMan nebula."

NGC 281 contains several distinct regions:

• an HII emission region Sharpless 184 of diameter 20 arcminutes containing the young galactic cluster IC 1590 centered about the OB star trapezium system HD5005.
• Two quite distinct CO molecular clouds:
• NGC 281 East: The southeastern CO region (N281A) with local standard of rest (LSR) similar to that of the HII region itself (-30.5 km/s vs. -26.5 km/s). This region contains highly recognizable “pillars of creation.” These pillars are known to contain newborn stars as a result of triggering from the nearby OB star trapezium system.
• NGC 281 West: (N281B), a molecular cloud in the southwestern region with three distinct clumps (NE, NW and S) (Megeath & Wilson 1997). The region is heavily obscured by dust and has a LSR (+44 km/s) quite different from that of its eastern neighbor and the HII region it borders.

• Lynn

### Two Scenarios for Star Formation

• Peggy

#### Spontaneous vs. Triggered Star Formation

• Most star formation begins due to spontaneous processes on a galactic scale, given sufficient time and material free fall will result in star formation.
• An outside source of energy can trigger the formation of a star before conditions become sufficient for free fall, leaving sequentially younger stars in its path while clouds broken into filaments by magnetic fields will show a filamentary pattern of protostars.

#### Star formation in a “controlled” environment

• small regions where the formation conditions except for the trigger are the same
• physical and geographical characteristics of protostars created can therefore be related to triggering mechanism.

#### NGC 281

• HII emission containing the young galactic cluster IC 1590, OB star trapezium system HD5005 with what appears to be two distinct start forming regions around it;
• Triggered East side with “pillars of creation”, newborn stars as a result of triggering from the nearby OB star trapezium system.
• Crowded West side with three distinct clumps (NE, NW and S) of star formation.

• Carol

### Spitzer data

Completing our analysis of the properties of the protostars in NGC 281 East and NGC 281 West required the analysis of 24 micron data taken from the Spitzer Space Telescope using MIPS. We obtained this data and photometry from the studies conducted by Scott Wolk et al. Using the Spitzer data and the 70, 100, and 160 microns data from the Hershel Observatory, we were able to create color-color diagrams of both the east and west candidate protostars. In addition, the Spitzer data allowed us to compare the SED slopes of the candidate protostars.

• Carol

• Lynn

### Final Source Selection

NGC 281 East--Identified over 100 possible sources by examining the 70 um FITS file in both DS9 and APT. In APT, we performed aperture photometry at 70, 100, and 160um of all possible sources. Then, in APT and DS9, we examined several features of the flux profile from each candidate protostar: (1) visual shape of the source and the surrounding dust and gas, (2) XY slices of the flux within the aperture, and (3) value of the full width-half maximum (FWHM). We plotted the distribution of the FWHM's to determine acceptable range of FWHMs for the aperture photometry in each band. Taking all of the above into consideration, we then determined 41 possible sources on the east side with 8 of them providing the most confidence given their shape, radial profile, and XY slices. We called these 8 our "yes" sources, and the other 33 our "maybe" sources. These are most likely sources, but do not inspire as much confidence.

• Peggy

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• Carol