The work reported on here was done as my Masters Thesis "Insights into high mass star formation from methanol maser observations."* at DePaul University, advised by Professor Anuj P. Sarma PhD, and was defended successfully on June 17th 2013. A full copy of it can be found on my Selected Works website

A powerpoint of talk which I gave for my thesis defense is here. I also have a video of the introductory explanation of my thesis.

To get an idea of what we mean by massive stars consider the sun. Astrophysicist measure mass in terms of masses of our sun. The sun is more massive than the combined mass of every other planet in the solar system. Among the star our sun is a runt. A massive star, one of the most if not the most massive star we know of is Eta Carinae which is over one hundred times the mass of our sun.

(Note in the above they are speaking of stars size.  However, a stars size does not relate to it's mass.  Eta Carinae has a mass of 120 solar masses, VY Canis Majoris has a mass of about seventeen solar masses.)

The study of these stars is difficult, as I explain in my video, and powerpoint, they form farther away, and in regions which are at least twice as distant and many times more obscured by dust and gasses. To study massive star formation we need to search for sources that are bright, compact, and intense enough to reach us through all the interference. Enter the Maser. Microwave Amplification by Stimulated Emission of Radiation. These sources are what my thesis focused on.

Astrophysical masers have certain physical properties which allow us to understand the conditions in the regions where they originate. For example, water masers are found where particles of water collide. One type of methanol maser is also found where particles collide. Another is found where particles are irradiated, such as near a protostar. Knowing these things allowed me to model where these masers may be in relation to a possible circumstellar disk and bipolar molecular outflow as shown in Figure

Figure 1:

Class I methanol masers are found in bipolar outflows where the outflow meets the ambient interstellar medium. Water masers are found either in outflows or in circumstellar disk. Class II methanol masers are pumped by radiation and so they are found near protostars. (Farmer, 2013)

The region G10.47+0.27 has been studied at multiple radio wavelengths as part of large surveys such as Hofner and Churchwell (1996); Caswell et al. (1995); Kurtz et al. (2004); Cesaroni et al. (1994); Wood and Churchwell (1989). This data has been cataloged for each spectral line or source type into massive catalogs such as Val'tts and Larionov (2007); Pestalozzi et al. (2005); Churchwell et al. (2009). One prior survey of hot ammonia near UC H II regions did suggest the presence of a young stellar object however their data alone was not sufficient to conclude that one existed at right ascension 18 08 38.2 and declination -19 51 50 (Cesaroni et al., 1994). Farmer (2013) compiled data from the catalogs Val'tts and Larionov (2007); Pestalozzi et al. (2005); Churchwell et al. (2009) and surveys Hofner and Churchwell (1996); Caswell et al. (1995); Kurtz et al. (2004); Cesaroni et al. (1994); Wood and Churchwell (1989), created maps and plotted line spectra for eight regions. This paper focuses on one of those regions.

Data sources

The positions of the 44 GHz Class I methanol masers were taken from the Val'tts and Larionov (2007) catalog. Most of the positions listed in this catalog were taken from VLA observations reported in Kurtz et al. (2004), from which we obtained information on the center velocities ( v LSR ) and intensities of the methanol masers. Kurtz et al. (2004) was a survey of forty-four star forming regions in search of 44 GHz Class I methanol masers with the goal of investigating the relationship between such masers and shocked molecular gas. The angular resolution of this survey was about 0.5 ′ ′ , and the velocity resolution was 0.17 km s -1 (corresponding to a frequency resolution of about 24 kHz). 

The Class II methanol maser data were taken from a catalog of 6.7 GHz Class II methanol masers compiled by Pestalozzi et al. (2005). This catalog contains 519 sources compiled from 62 references in the literature. Pestalozzi et al. (2005) found that Class II methanol masers trace the molecular ring of our galaxy where massive OB star associations are found, in agreement with the idea that methanol masers are clearly associated with high mass star formation. Pestalozzi et al. (2005) relied heavily on Caswell et al. (1995), which was a survey of thirty-six sites of 6.7 GHz methanol masers and forty sites of 1.7 GHz OH masers, conducted with the Australia Telescope Compact Array (ATCA). The purpose of this survey was to study the relationship between OH and CH 3 OH masers and the evolution of massive stars. The angular resolution of the methanol maser observations was about 1.5 ′ ′ , the frequency resolution was 0.97 kHz, and the rms noise was 60 mJy beam -1 .

The H 2 O maser data were taken from Hofner and Churchwell (1996) who obtained images and spectra for 21 H 2 O maser sources in the vicinity of UC H II regions by observing with the VLA at 22 GHz. The angular resolution of their survey was 0.4 ′ ′ , the frequency resolution was 24 kHz ( ≡ 3.5 km s -1 ), and the typical RMS noise was 30 mJy beam -1 .

Almost all of the UC H II region data were taken from Wood and Churchwell (1989), who surveyed seventy-five UC H II regions with the VLA at frequencies of 4.9 GHz and 14.9 GHz. The goal of this survey was to understand the morphology and characteristics of the selected H II regions. The 14.9 GHz observations used for this thesis have an angular resolution of approximately 0.4 ′ ′ and an rms noise of about 0.32 mJy beam -1 . 

The 4.5 μ m infrared data used were taken from the GLIMPSE catalog of the online Spitzer archive (where GLIMPSE stands for Galactic Legacy Infrared Midplane Survey Extraordinaire). The GLIMPSE catalog (Churchwell et al., 2009) was compiled from observations taken with the Infrared Array Camera (IRAC)on board the Spitzer Space Telescope , which recorded data at wavelenghts of 3.6 μ m, 4.5 μ m, 5.8 μ m, and 8.0 μ m. The angular resolution of GLIMPSE images is about 1.2 ′ ′ . We use the 4.5 μ m data because Cyganowski et al. (2009) have found that extended emission at 4.5 μ m is associated with high mass star forming regions. This wavelength is usually colored green in most false color infrared images, hence the term extended “green” objects (EGO's).

Results

Figure 2 shows the Class II methanol maser and the Class I methanol maser in G10.47+0.27, together with other sources of interest. The Class II methanol maser is located to the southeast of the Class I maser position, and its position is marked by a square in Figure 2. The Class I and Class II masers are separated by about 15. 3 ′ ′ ; at a distance of 6.0 kpc to G10.47+0.27 (Pestalozzi et al., 2005) , this is equivalent to about 0.44 pc. Two of the H 2 O masers in this source are almost coincident with the Class II methanol maser, and a third is right next to it. There are three UC H II regions, two of which are almost coincident with the Class II methanol maser, and a third lies to the northeast of it. A line of strong 4.5 μ m point sources lies to the east and southeast of the Class I methanol maser. The positions of these sources, together with the telescopes used to observe them and the angular resolution in terms of synthesized beam of the observations, are listed in Table 1. Data in Table 1 were assembled from Kurtz et al. (2004) Caswell et al. (1995) Hofner and Churchwell (1996)and Wood and Churchwell (1989).)

The center velocities ( v LSR ) and intensities of the Class I and Class II methanol masers and H 2 O masers have been plotted in Figure 2. All the three H 2 O masers shown in this figure are at smaller v LSR (i.e., blueshifted) than the Class II methanol maser. The Class I methanol maser is also blueshifted with respect to the Class II methanol maser.

Figure 2:

Figure showing the Class II and the Class I methanol maser and other sources of interest in region G10.47+0.27. The position of the Class I methanol maser is indicated by a diamond and the Class II methanol maser by a square. The open circles mark the positions of the H 2 O masers and the × 's mark the peaks of the UC H II regions. In all cases, positional uncertainties are either equal to or smaller than the sizes of the markers themselves or are marked by a cross, if larger than the marker sizes. The grayscale shows the 4.5 μ m Spitzer infrared image and the intensity range is between 2.22 MJy sr -1 and 1100 MJy sr -1 .(Farmer, 2013)

Figure 3:

Plot of intensities and center velocities ( v LSR ) of methanol and H 2 O masers associated with G10.47+0.27. At the top of each line is a symbol indicating the type of source; the Class I methanol maser is represented by a diamond, the Class II methanol maser by a triangle, and the H 2 O masers by filled circles.(Farmer, 2013)

Table 1:

Positions and associated information for sources associated with G10.47+0.27.

Source Type	R.A. (J2000)	Dec. (J2000)	Observing	Synthesized	Kinematics
	(h m s)	( o ' ” )	Telescope	Beam	v LSR (km s -1 )	Intensity (Jy)
44 GHz Class I CH 3 OH maser	18 08 37.4	-19 51 40	VLA	3.1 4 ′ ′ × 1.3 3 ′ ′	67	1.9
6.7 GHz Class II CH 3 OH maser	18 08 38.2	-19 51 50	ATCA	1. 5 ′ ′ × 1. 5 ′ ′	75	120
22 GHz H 2 O maser	18 08 38.2	-19 51 50	VLA	0.4 8 ′ ′ × 0.4 5 ′ ′	64	200
22 GHz H 2 O maser	18 08 38.2	-19 51 50	VLA	0.4 8 ′ ′ × 0.4 5 ′ ′	63	14
22 GHz H 2 O maser	18 08 38.2	-19 51 49	VLA	0.4 8 ′ ′ × 0.4 5 ′ ′	70	28
14.9 GHz UCHII region	18 08 38.2	-19 51 50	VLA	0.8 9 ′ ′ × 0.5 7 ′ ′	-	-
14.9 GHz UCHII region	18 08 38.2	-19 51 49	VLA	0.7 9 ′ ′ × 0.5 6 ′ ′	-	-
14.9 GHz UCHII region	18 08 38.3	-19 51 45	VLA	1.0 4 ′ ′ × 0.7 9 ′ ′	-	-

Modeling

A model of this star forming core based on the morphology of methanol and H 2 O masers in G10.47+0.27 can be constructed. Figure 3 shows the model of the disk and outflow, together with the locations of the Class II and Class I methanol masers, and the H 2 O masers. We have chosen to put the information from G10.47+0.27 into Figure 3. We interpret the H 2 O masers to be located in a circumstellar disk together with the Class II methanol maser, with the Class I methanol maser located in the outflow. This is a reasonable interpretation for G10.47+0.27, where the H 2 O masers are clustered close to the Class II methanol maser (Figure 2).

Figure 4:

Diagram of our disk-outflow model for this region, showing the locations of the Class II and I methanol masers and the H 2 O masers. We have chosen to put the information from the G10.47 star forming region (Figure 2 and Table 1) in this figure. Masers that are blueshifted with respect to the Class II methanol maser, which we take to be near the location of the protostar are shown in blue.

Conclusions

The complex of sources at Right ascension 18h 08m 38.2s and Declination -19 o 51 ′ 50 ′ ′ taken with the 4.5 micrometer Spitzer infrared data indicates the presence of a massive young stellar object at that location. One other paper,Cesaroni et al. (1994), hinted at this finding, but did not have enough data to make the conclusion. The thesis, Farmer (2013), compiled data on this same location which had previously been published. The only reasonable conclusion from the maser data, the spitzer data, and the UC H II region data in this location is the presence of a massive young stellar object. Other phenomena can cause any one of these effects, only one we know of can cause all of them in such a compact area.

[Acknowledgements] This work builds on a thesis, Farmer (2013) supervised by Professor Anuj P. Sarma PhD at DePaul university. Under his guidance the author learned everything they know about astronomy. Without his help this would not have been possible. 

References

Caswell et al. 1995   Caswell, J.~L. and Vaile, R.~A. and Ellingsen, S.~P. and Whiteoak, J.~B. and Norris, R.~P., "Galactic methanol masers at 6.6 GHz", (1995), 96-138.

Cesaroni et al. 1994  Cesaroni, R. and Churchwell, E. and Hofner, P. and Walmsley, C.~M. and Kurtz, S., "Hot ammonia towards compact HII regions", (1994), 903-920.

Churchwell et al. 2009  Churchwell, E. and Babler, B.~L. and Meade, M.~R. and Whitney, B.~A. and Benjamin, R. and Indebetouw, R. and Cyganowski, C. and Robitaille, T.~P. and Povich, M. and Watson, C. and Bracker, S., "The Spitzer/GLIMPSE Surveys: A New View of the Milky Way", (2009), 213-230.

Cyganowski et al. 2009  Cyganowski, C.~J. and Brogan, C.~L. and Hunter, T.~R. and Churchwell, E., "A Class I and Class II CH$_{3}$OH Maser Survey of EGOs from the GLIMPSE Survey", (2009), 1615-1647.

Farmer 2013  Hontas Freeman Farmer, "Insights into high mass star formation from methanol maser observations." (2013).

Hofner and Churchwell 1996  Hofner, P. and Churchwell, E., "A survey of water maser emission toward ultracompact HII regions.", (1996), 283-299.

Kurtz et al. 2004  Kurtz, S. and Hofner, P. and √Ålvarez, C.~V., "A Catalog of CH$_{3}$OH 7$_{0}$-6$_{1}$ A$^{+}$ Maser Sources in Massive Star-forming Regions", (2004), 149-165.

Pestalozzi et al. 2005  Pestalozzi, M.~R. and Minier, V. and Booth, R.~S., "A general catalogue of 6.7-GHz methanol masers. I. Data.", (2005), 737-742.

Val'tts and Larionov 2007  Val'tts, I.~E. and Larionov, G.~M., "A general catalog of class I methanol masers", Astronomy Reports (2007), 519-530.

Wood and Churchwell 1989  Wood, D.~O.~S. and Churchwell, E., "The morphologies and physical properties of ultracompact H II regions", (1989), 831-895.

*Updated to link to the official libraries electronic copy of my thesis. 

UPDATE:

I have got a preprint of a comprehensive, edited and updated, paper based on my MS thesis on the ArXiv.  It has also been submitted to a journal for formal peer review.  http://arxiv.org/abs/1311.3983

An independent work largely agree's with my findings.  http://arxiv.org/abs/1308.4167 The sort of phenomena I found in the data is quite real