Introduction

The study of star forming regions are very important in understanding how stars are formed and how they function. This increases our understanding of stars and assists us in the question of how the universe is evolving. The region in which stars are formed are normally dense clouds of dust which begin to collapse under an increasing gravitational force. This forms heat which accumalates in the core to commence the process of nuclear fusion. Once the star has commenced nuclear fusion, the dust is swept away by radiation pressure and an expanding region of hydrogen (H_II) is formed. The star begins to radiate heat which is mostly absorbed by the dust surrounding it. These molecules are broken down due to the UV radiation which is emitted by stars. Since the dust clouds block out the majority of radiation, compounds can survive in the gas phase. One of these compounds is methanol (methyl alcohol). Another is the hydroxyl radical (OH). Some radiation does pass through the dust clouds, which is of a low frequency (microwaves and radiowaves). This radiation hits particles of methanol and hydroxyl ions which then amplify the wave to create radiation which is easily picked up by radio telescopes (Very Long Baseline Interferometers), such as the EVN (European VLBI Network). These molecular clouds which amplify the long wave electromagnetic radiation are known as MASERs (Microwave Amplification by Stimulated Emission of Radiation). By observing the pattern these MASERs make, the characteristics of the star forming regions can be known. If the star has finished accreting, the MASERs gradually move away from the cloud, as the radiation exerts a force on the particles sufficient to overcome gravity. If the star is still accreting, MASERs gradually move inward. The star at the centre of W3(OH) is most likely to be a protostar which is capable of forcing material away but pulls material in on a spinning axis. This way, the star can still be accreting yet still be pushing some material away. Through measurements of the motions of gas surrounding the W3(OH) protostar(s), the characteristics of the star can be learned.

W3(OH) dust cloud

The W3(OH) dust cloud is located on the Perseus arm of our galaxy. This cloud is roughly 2200 parsecs away (7172 light years or 6.79x10¹⁹ kilometres). This cloud was studied in 1992 by Dr. Karl Menten, who was studying MASERs which emitted a frequency 6.668 GHz. Menten was the first to discover the MASERs at this frequency, prior to this methanol MASERs at 12.2 GHz were commonly used to trace massive star formation. Since Menten recorded the location of the MASERs in 1992, we compared the location of MASERs that we found in 2007. The difference in the two epochs is 15 years and shows significant movement of the MASERs. Since the W3(OH) cloud can only be seen in the northern sky, the EVN was used to observe the MASERs. We plotted the positions of the MASERs on a map and compared with the results from 1992. The results revealed the motion of the cloud. A previous paper on this cloud by Jonathan Kawamura and Colin Masson expressed that the cloud was expanding at a rate of 3-5 km/s by measuring how the brightest patches of the cloud were moving (1998). This was very similar to the expansion speed measured by Bloemhof et al (1992) who used hydroxyl MASERs. By investigating how much the methanol MASERs have moved in the cloud, the rate of expansion expressed by Kawamura et al can be tested.

Method

The images from the EVN were calibrated and then the positions of the MASERs were found using a program called 'ORFIT'. We singled out the possible MASERs and the program then identified the position of the MASER in the image. The MASER was marked and the program recorded its location and the frequency in which the MASER was found. After all the MASERs had been identified, the relative sky 'co-ordinates' were converted real 'co-ordinates' known as Right Ascension (R.A.) and Declination. With the real R.A. and Dec. of the MASERs, our results and Menten's results were compared. These results were plotted onto a map and were compared visually.

Results

The results, as seen in the map, show what appears to be a slight expansion and clear movement of the MASERs. These have moved from the centre which is shown by the image showing the different concentrations of hydrogen ions. The brightest section of the cloud is the concentrated area of MASERs (Fig.2), in the centre which is at 02^o 27' 3.84" RA and 61^o 52' 25.3" Dec. This area of MASERs is actually infront of the cloud, from our perspective, which means that it would have to move in our direction if expanding (which can be detected through blueshift). The MASERs infront of the cloud do not appear to have moved greatly due to their velocity being parallel to the line of sight, however in reality, they have moved greatly in our direction. The difference in angle needed to support the results of Kawamura et al would have to be from 4 mas (milli arc seconds or one thousandth of an arc second) to 7 mas (1 arc second=1/3600 of a degree). Most of the MASERs have moved over 3 mas, which shows consistency with Kawamura's work. Note Fig.3 which shows how the MASERs have spread outward in a linear fashion around 5 mas at position angle of 50^o. There appears to be no proper motion in the perpendicular direction. This could be interpreted as a bipolar outflow from a central massive star. An alternative explanation for this linear pattern is that there is a circumstellar disc rotating around the star which is composed of these MASERs, which would explain why the MASERs are positioned in a linear pattern.

Conclusion

The results from this experiment support the previous estimates made by Bloemhof and Kawamura independently. Since these three results were obtained using three different methods, the impression given is that cloud is expanding at a rate of 3-5 km/s anisotropically. The fact that the cloud is expanding requires us to explain this phenomenon. There must be a star inside the cloud, which is creating the H_II region. The star is pushing the dust away as the photons hit the dust particles. From the rate of expansion, it is estimated that the cloud has been expanding for roughly 2300 years (Kawamura et al), which would make it a very young star. The central region shows evidence that a bipolar outflow is present which is forcing the methanol MASERs outwards.

Acknowledgement

We thank Dr. Karl Menten for supplying the 1992 MASER data and the JIVE staff for their assistance.