EUROPEAN EDUCATIONAL PROGRAMME
"CATH A STAR"
PROJECT: Pinwheel Galaxy M101

Contents:
1. Introduction
2. Historical information
3. Scientific file of M101
4. How did scientists receive
the information
5. Observations of M101:
· CCD observstions
6. Comparison between M101 and M31
7.Exercise: Work with a telescope for
detection of galaxy M101 with 50/70 cm Schmidt telescope in NAO-Rozhen.
8. Conclusion

1. Introduction
The constellation of Ursa Major is the site of a spiral galaxy known as M101. This a nearly face-on spiral with a bright center and symmetric shape. It is located about 27 million light years from Earth. With an estimated linear diameter of over 170,000 light years, this is one of the largest disk galaxies known. M101 is a bright object with a magnitude of 7.9. It is easily visible in binoculars and small telescopes. To be seen the galaxy's faint spiral arms it should be use an instrument larger than 4-inches.
This spiral Sc spiral NGC 5457 or Messier 101 has several extremely luminous star-forming (H II) regions in the outer spiral arms, some sporting their own NGC numbers.
It dominates a small group of galaxies, with some of its neighbors such as NGC 5474 showing wear and tear attributed to the tidal effects of M101. M101 itself is further noteworthy for its extensive and lopsided distribution of neutral hydrogen gas, and for showing evidence of gas falling into its disk at high speeds.

Fig.2 Constellation Ursa Major

2. Historical information
M101 was discovered by Pierre Mechain on March 27, 1781, and added as one of the last entries in Charles Messier's catalog. It was among the first "spiral nebulae" identified as such by William Parsons, the third Earl of Rosse.
Although extended 22 arc minutes on photos and quite bright, only the central region of this galaxy is visible in smaller telescopes, best at low powers. Suggestions of the spiral arms can be glimpsed in telescopes starting from 4 inch as nebulous patches. Several of these patches (i.e., spiral arm fragments) were assigned their own catalog numbers by William Herschel and later observers; according to the NGC and Burnham, there are 9 such numbers, 3 of which go back to Herschel who has found them on April 14, 1789, while the RNGC states that five of the others don't exist (ne); it mentions however that deVaucouleurs has them as knots: NGC 5447 (H III.787), 5449 (ne), 5450 (ne), 5451 (ne), 5453 (ne), 5455, 5458 (ne), 5461 (H III.788), 5462 (H III.789), and 5471.
During the previous century astronomers made sketches of the galaxy. Very interesting are Lord Rosse's drawings of M101.
Drawing of the Pinwheel Galaxy M101 by S. Hunter, based on observations by William Parsons, the Third Earl of Rosse. Lord Rosse describes this object as "Large, spiral, faintish; several arms and knots. 14' diameter at least."

3.Scientific portrait of M101 Galaxy in Ursa Major

Common Name : Pinwheel Galaxy
NGC Number : 5457
Visual Magnitude : 7.9
ra : 14h 03.2m dec : +54° 21'


M101, one of the Messier Objects, is a Pinwheel Galaxy located in the
constellation, Ursa Major. Its Right Ascension (hrs:min) is 14:03.2. Its
Declination (deg:min) is +54:21. This means that right now (July/August)
from Earth you would see it in the northwestern sky at night.
Although it is the brightest of a group of at least 9 galaxies, from a
low-powered telescope on Earth, only its center is visible to the eye. Yet,
M101 is revealed as one of the most noticeable Grand Design spirals in the
sky. Visually, it is very symmetrical, yet its core is considerably displaced
from the center of the disk.

 

 

 






10 percent higher value (27 million light years). At the new distance from the HST and Hipparcos, it has a linear diameter of over 170,000 light years and is thus among the biggest disk galaxies, and its total apparent visual brightness of 7.9 mag corresponds to an absolute brightness of -21.6 magnitudes, or a luminosity of about 30 billion (3*10^10) times that of our sun.
Messier 101 is a spectacular and nearby spiral galaxy located in Ursa Major,
and is also known as the Pinwheel Galaxy. This galaxy is nearly twice the
diameter of our own Milky Way Galaxy, and has a less prominent central bulge.
The galaxy diameter is about two thirds that of the full moon.
The face-on orientation of Messier 101 allows us to easily identify the primary
constituents of a spiral galaxy: a bright nucleus contained within a central bulge,
surrounded by a thin disk that contains the spiral arms. Regions of patchy
illumination within the arms serve as signposts of recent star formation, and are
referred to as giant H II regions.
Moreover, dust lanes within the arms are also seen. It is this dust, accompanied
by molecular and atomic gas (invisible at optical wavelengths), which provide
the raw materials for future star formation. Note how the spiral arms wind all
the way in towards the inner disk in the long-exposure DSS photograph.

SUPERNOVA IN M101
Three supernovae have been discovered in M101: The first one, SN 1909A,
appeared on Jan 26, 1909 and was discovered by Max Wolf; it was of peculiar
type and reached mag 12.1 (Glyn Jones reports that the discovery took place
in February, and the SN reached only mag 13.5). The second supernova
1951H was of type II, occurred in September 1951 and reached mag 17.5,
while the third, SN 1970G, also type II, occurred on Jul 30, 1970 and
reached mag 11.5.

4.How did scientists receive the information
Astronomers observe M101 with telescopes in all lengths of the waves.
On Astronomy Picture of the Day we can see an incredible photo, from which scientists obtain a lot of information about the galaxy. This giant spiral galaxy, Messier 101 (M101), was photographed by the Ultraviolet Imaging Telescope (UIT). UIT flew into orbit as part of the Astro 2 mission on-board the Space Shuttle Endeavour in March 1995. The image has been processed so that the colors (purple to white) represent an increasing intensity of ultraviolet light. Pictures of galaxies like this one show mainly clouds of gas containing newly formed stars many times more massive than the sun, which glow strongly in ultraviolet light. In contrast, visible light pictures of galaxies tend to be dominated by the yellow and red light of older stars. Ultraviolet light, invisible to the human eye, is blocked by ozone in the atmosphere so ultraviolet pictures of celestial objects must be taken from space.

For example: Color photos made with large telescopes of the galaxy M101
reveals a very bright mucleus of the galaxy. The hottest stars are blue-white in
color and are the youngest and most massive stars. The color image clearly
reveals that these are the types of star that are preferentially born within the
spiral arms of galaxies. Astronomers established that in the near-Infra Red,
the spiral design of Messier 101 is still obvious. However, the contrast within
the spiral arms is considerably reduced because of two reasons. First,
near-infrared light is able to pierce through most of the obscuring effects of
dark dust within the spiral arms. Second, near-IR wavelengths preferentially
detect cooler and redder stars. Astronomers learned earlier that the luminosity
within spiral arms is primarily due to hotter and bluer stars. In other words, the peak emission in the spiral arms is outside the near-infrared filter and falls within the visible-light region. It is for these reasons that Messier 101 appears more impressive in the visible light photographs than in the near-infrared.

M101 has been observed in X-Ray by ROSAT satellite.
At even shorter x-ray wavelengths, the spectacular appearance of Messier 101 fades almost nothing. This image is dominated by electronic noise, similar to static on your AM radio, and the blue-black variations in the pixels are nothing more than random noise. A small number of weak sources (denoted in white and yellow) are perceptible above the background. The fuzziest and dimmest emissions regions near the center are probably associated with the disk of M101. The point-like sources scattered near the edges of
the image could either be due to weak emission from H II regions within the arms of M101, or strong emission from much more distant quasars.


5.Observations of M101:
We observed this galaxy during the summer school in NAO-Rozhen with 50/70 cm Schmidt telescope and CCD ST8. We learned how to work with the telescope and to direct the telescope to definite objects and to guide the telescope according to the time when the images were received. We learned to work with the software of the CCD camera and to make images. We made several images of the galaxy in V and R filters. The best images were received with exposition 180 sec and 300 sec.
Here are the best images:

...................
Fig.8 Galaxy M101- 06/15/2002 exp=120sec; Filter R
.................... Fig.9 : Galaxy M101- 06/16/2002
20h 07min exp=300sec; Filter R

....................
Fig 10 : Galaxy M101 06/15/2002 exp=120 sec; Filter V ....................... Fig.11: Galaxy M101 05/15/2002 01h55min exp=300 sec; Filter V

Animation of Galaxy M101- 2 images in Filter R, exp= 180 sec

.. ....
Fig. 12: Galaxy M101- 06/15/2002 . Fig.13: Galaxy M101- 06/16/2002

Animation of Galaxy M101- 2 images in Filter V, exp= 180 sec

.. ..
Fig.14: Galaxy M101- 06/15/2002 Fig.15: Galaxy M101- 07/31/2002

Using these animations we searched for supernovae in the galaxy M101. Unfortunately we didn't find supernovae on these images.:-)

6. Comparison between M101 and M31

7. Exercise: Detection of galaxy M101 with 50/70 Schmidt telescope in
NAO-Rozhen.

The goal of this exercise is to show how observation with a telescope (here with
50/70 Schmidt telescope) can be done. The goal is introduction to the construction
of the telescope and with the coordinates of the telescope as well.

Fig. 3: Drawing of galaxy M101


Fig.5: Galaxy M101



Fig.6: Supernova in M101

The distance of M101 has been determined by the measurement of Cepheid variables with the Hubble Space Telescope in 1994/95 to be about 24 +/- 2 million light years, by the HST H0 Key Project Team. Kenneth Glyn Jones mentions earlier Earth-bound attempts of 1986, when two Cepheids were claimed to have been detected (yielding distance estimates between 20 and 26 million light years). It is also in good agreement with a distance determined from the Planetary Nebula Luminosity function, by Feldmeier, Ciardullo and Jacoby which is 25.1 +/- 1.6 million light years. According to the recent recalibration of the Cepheid distance scale, the "true" distance of M101 should be closer to a


Fig. 4: Galaxy M101


Fig. 17: An observer

Preparation of the equatorial coordinates of M101 for
guidance and detection of the object.

Step 1: Introduction to the construction of the telescope;
detection of 50 cm Schmidt plate, 70 cm mirror and CCD
camera ST8 that is found in the focus of the telescope (focus distance = 172 cm).
Step 2: Introduction to a 20 cm refractor- the guide of the telescope and a 5 cm telescope-a seeker in the telescope.
Step 3: Examination of the circle of declination and the circle for hour angle.
Step 4: Determination of the type of coordinate system that is used in the telescope. For Schmidt telescope this is an equatorial coordinate system.
Step 5: Preparation of the equatorial coordinates of the object used for guidance of the telescope. Calculation of time angle with the help of known Right Ascension and stellar time. The following formula is used here:
time angle= stellar time- Right Ascension
Step 6: Setting of declination and time angle on the respective circles of the telescope and guidance of the telescope to the object.
Step 7: Detection of the object in the guide of the telescope. The galaxy is seen as a dim spot.
When the telescope is directed to the object, creation of images with the CCD camera can start.
One model of a task is observation of M101 for searching of supernovae.
The simplest way for searching for superovae is creation of images form different months and then creation of an animation using these images. If someone looks carefully at the animation, stars that increase their brightness - eventually supernova- can be found.


Fig.18: Schmidt telescope in NAO-Rozhen

Fig.19: Schmidt plate of the telescope

Fig.20: Schmidt
telescope

8.Conclusion
The galaxy M101 is one of the most beautiful galaxies, one of the small number of similar
objects that can be seen with a small telescope or a binoculars. The most interesting things in
our work over the project were the observations of M101 that we made with Schmidt
telescope in NAO-Rozhen.
We want to continue our observations of M101 because we think that searching for supernovae
in galaxies is very interesting. M101 is a very interesting and appropriate for searching for
supernovae galaxy. Our observations of the galaxy continue...

 

References:
http://antwrp.gsfc.nasa.gov/apod/lib/about_apod.html
http://www.aas.org/publications/baas/v30n4/aas193/S210.htm
http://www.e-z.net/~haworth/messier/index.html
http://www.astr.ua.edu/gallery2t.html
http://www.pbase.com/ronson/rozhen_082002

For contacts:
Student:
Traian Petkov
Leader:
Veselka Radeva: Astronomical Observatory-Varna, Bulgaria
radevi@mail.varna.techno-link.com

 


Fig.21: Galaxy M101

Fig.1: Pinwheel
Galaxy M101
Best seen with Microsoft Internet Explorer

Fig.7: Galaxy M101
Special thanks to the National Astronomical Observatory - Rozhen for their help
and to Nadezhda Lyubomirova
for translation in English and web-design!

Fig.16: Galaxy M31