Tuesday, February 11, 2014

Star of the Week: Altair

Returning once more to the Summer Triangle, I'd like to introduce readers to Altair.

Altair (false color) imaged by MIRC at the CHARA Array on Mt. Wilson
Credit: John Monnier (University of Michigan)

Altair has the distinction of being one of the few stars (besides the Sun) which has been directly imaged. What you're looking at there, in false color, is a reconstructed image of Altair from observations with the CHARA (Center for High Angular Resolution Astronomy) Array, an array of 1m telescopes that uses the combined light from each instrument to collect high resolution observations of astronomical objects. In a sense it acts like a much larger telescope and I'll explain CHARA here in an upcoming post.

Altair is the brightest star in Aquila and is classified as A7V star. It is 16.7 ly from Earth, a neighbor and a close one at that on a galactic scale.  If you look at the picture above, something that should be noticeable is that Altair is not spherical. This is because it rotates at a high speed. Since stars are made of gas, a rapidly rotating star will have it's shape altered by the motion, bulging outward. You might also notice that there are light and dark spots. This indicates areas where the star is different luminosities (white being more luminous). This is because luminosity and temperature are related to surface gravity, which in turn depends on mass and radius. In Altair, the surface gravity is lower at the radius, meaning there is lower gas pressure, cooling the gas there and decreasing luminosity.

Monday, January 20, 2014

Updates for the coming months

A 'rite of passage' for many graduate students are the qualifying (sometimes called comprehensive) exams they must pass as part of their program. The details of these exams vary by department but the universal trait is that they are among the most difficult moments in graduate school. This coming semester I have my second (and most comprehensive) round of qualifying exams.

Because of the exams, I might not post all that much, but I do intend on posting more than I did last semester (not at all!) because the exams cover all of astronomy and what better way to review all of astronomy than by sharing bits of it with others via introductions to various stars? So, although the Summer Triangle is long gone, there will soon be the promised introduction to Altair.