In the final image from the Fall 2020 “Observational Astrophysics” class, we see another version of processing Hercules globular cluster data, from Shoaib Shamsi ’21.
Shoaib explains “Messier 13, or the Hercules cluster is a globular cluster of hundreds of thousands of stars in the Hercules constellation. A globular cluster is a tight collection of stars with an approximately spherical arrangement, bound to each other by gravity. These clusters are usually located orthogonally to a galaxy’s disk and often feature old stars. M13 is estimated to be about 11.7 billion years old – among the oldest objects in our galaxy. Often regarded as the finest globular cluster in the northern sky, M13 is located a mere 6.6 Kpc away with an apparent magnitude of 5.8.
We can find the Hercules cluster about one third of the way from Vega to Arcturus. Images were taken in the g, r, and i filters with 3 40s exposures for each filter. The images were taken with our Meade 16” SCT along with the FLI ProLine 16803 CCD. The cluster’s angular diameter is around 16.6’, and with our CCD we can view our images at around 0.46″ / pixels.”
Almost finished with our series of images made by students in the Fall 2020 “Advanced Observational Astrophysics” class.
Here’s an image made by Miranda Kong, BMC’22 using data of part of the Double Star cluster in Perseus I took over the summer.
Miranda explains: “We have used backup data for the Perseus Cluster taken by Professor Karen Masters at the Strawbridge Observatory with the 16” telescope and 4096×4096 pixels CCD. The images are taken in g, r, and i filters.
I have produced the 3-color combined image using the data. For the combination process, since the i filter indicates infrared wavelengths, I have assigned the color red to the i-filter images. Therefore, my color scheme is shifted, so I need to assign magenta to r (red), and cyan to g (green), i.e. the whole spectra is shifted blue for a little. This produced a decently balance image of which I could adjust the 3 filters to form an image of black background, and stars predominantly white. However, some of the star do appear more red or more blue (especially the small ones) than others. Since these data are just taken with gri filters, a star appearing more blue in this image simply says that it emits more blue light than other colors, i.e. its color spectrum peaks at blue. By black body radiation, we know that hotter stars tend to peak at the bluer end of the spectrum. ”
For her assignment, Kate Gold BMC ’21 chose to use Hubble Space telescope data to put together with her own colour choices. I think the result is beautiful.
Kate explains: “The image above shows the Eagle Nebula (M16, NGC 6611) as observed by the Hubble Space Telescope Wide Field and Planetary Camera 2. The Eagle Nebula is in the constellation Serpens and is 7000 light years away. It contains over 8000 stars. This image contains the “Pillars of Creation” region; the pillars are made of dense cool molecular hydrogen gas and dust. The pillars are so dense that the interior gas contracts due to gravity and forms stars. The tops of the pillars contain young stars which and little low density material. The image is a compilation of observations from three optical bands: O[iii], Ha, and S[ii] shown in red, green, and blue respectively.”
Here’s another beautiful Helix Nebula image, this one by Julian Goddy ’21.
Julian explains, “The Helix nebula (NGC 7293) is a planetary nebula 650 light years away and 4 light years across in the constellation Aquarius. It is the closest example we have of the planetary nebula from a sun-like star. Planetary nebulae got their name because they looked round like planets when they were first imaged with a small telescope. However, planetary nebulae are not actually planets, but rather the remnants of stars after they have run out of fuel. When this happens, the outer gaseous layers end up getting blown into space, leaving behind a dense hot core called a white dwarf. The hot glow from the white dwarf heats up the expelled gas and causes it to shine. This shining gas is what we see as a planetary nebula such as the Helix. In around 10,000 years, the Helix will no longer be visible because the gas will drift away from the white dwarf and contribute to the recycling of atoms in space.
Due to the dimness of distant objects in space, astronomical images are usually taken in a series of filters that are all greyscale to increase their sensitivity. These filters each detect a particular element in the object. Together, they give a more complete image of its structure. Multiple images are taken in each filter and then aligned and stacked on each other to increase the signal to noise ratio. The images from these filters are then each assigned a different color and then aligned and superimposed on each other to create the final image. In this composite three-color RGB image, Ha is red, doubly ionized oxygen [OIII] is green and singly ionized sulfur [SII)] is blue. Eleven images with 120 second exposures were taken for each filter with the Proline PL 16803 CCD on the 16” telescope at Haverford College’s Strawbridge Observatory. These images were then aligned and stacked together using AstroImageJ. The image was taken on September 19, 2020.”
Here’s a version of the Ring Nebula, composed by Kevin Sang ’22 using data I took in the summer.
Kevin explains “This is a composite image of Messier 57/NGC 6720, also known as the Ring Nebula. The Ring Nebula is roughly 2,600 lightyears away and has an apparent magnitude of 8.8. It is a planetary nebula made up of ionized gas surrounding a stellar object that is evolving to become a white dwarf.
The image is taken using a 16-inch optical telescope and a Charged Coupled Device (CCD). The CCD consists of many individual pixel cells, each of which counts the amount of photons that it receives over a period of exposure time. Combined with SII, H-alpha, and OIII filters, images of the Ring Nebula in different wavelengths can be captured, and by using AstroImageJ, we composed a RGB image of it.”
Continuing our series of student observations, here’s the Dumbbell nebula, by Karla Garcia ’21 .
Karla explains “The Dumbbell Nebula is a planetary nebula located in the Vulpecula constellation. A planetary nebula consists of a shell of ionized gas surrounding an aging star, which ejects said gas in the late stages of its life. The images were taken from 9:45 pm to 12:00 am on September 30th, 2020, from the 16” telescope at the Strawbridge Observatory in Haverford, PA. Three filters were used: the OIII filter corresponds to the green layer, the Halpha filter corresponds to the red layer, and the infrared filter corresponds to the white layer. The green layer shows the high ionization of oxygen in the nebula, the red layer shows the ionized hydrogen which is due to the the Dumbbell Nebula’s hot blue central star, and the infrared filter shows the intense ultraviolet radiation from the central star (whose temperature is 85,000 Kelvin) and gives the nebula image its dumbbell shape.”
Earlier this month, the student led Public Observing team ran a virtual public observing night, with the theme “Constellations from Many Cultures”. Videos from this event, which was live streamed to our new YouTube Channel can be viewed:
Here is a lovely view of the Hercules cluster, from imaging taken by Nathan Wolthuis ’21, and his co-observers earlier this semester.
Nathan explains: “This is a 3 color image (B,r, & i) of the Hercules globular cluster (M13). Globular clusters are groups of stars tightly bound by their gravitational fields that orbit galactic cores. Globular cluster gravitational fields are quite dense, which results in the populations taking on a spherical shape. It should be noted that this globular cluster in particular has many ancient low mass stars, primarily reds and yellows especially in the center. This is further reinforced through the younger bluer (and more metallic) stars having a tendency to diffuse outwards, which can be seen in the image. This image was taken using a FLI Proline CCD and 16” telescope, with the B filter assigned as blue, r a s green, and i as red.”
This image by Elizabeth Warrick, BMC ’21 is her second attempt at imaging the Triangulum galaxy, the first one foiled by pointing issues. I’d like to applaud Elizabeth for her persistence in getting this tricky image.
Elizabeth explains: “The Triangulum Galaxy is a very beautiful spiral galaxy that shows the wonderful structure galaxies can hold in the night sky. In this image you see a picture of the Triangulum Galaxy (lower right quadrant) imaged in the g,r, and i filters respectively. The filters I chose to observe allow us to look at the galaxy overall using the g,r, and i filters to get a good look at the wavelengths of light. Notice the faint spiral arm structure coming out of the slightly brighter center of the galaxy.”