RX Andromedae is an excellent example of the Z Camelopardalis class of dwarf novae, aka the "Z Cam stars". These stars are like other dwarf novae in that they undergo outbursts of several magnitudes, lasting for days to a few weeks, caused by their disks rapidly increasing in...
February 7, 2011 - 11:06am
RX Pup is a symbiotic star -- a binary star system composed of a giant star and a small companion onto which wind from the giant star accretes. Their spectra are composite spectra, showing features typical of both cool, giant stars (the donor star), and of hot dwarf stars (the accreting...
May 30, 2012 - 9:28am
RY Sagittarius is a fine R Coronae Borealis star coming back into easy view as we enter the Milky Way bulge season. The R CrB stars are highly evolved objects whose origin remains somewhat mysterious. They are perhaps the product of the merger of two white dwarf stars, or are...
November 6, 2012 - 12:51pm
RZ Vul is an interesting RV Tauri star of the RVB subclass. The RV Tauri stars are highly evolved giant stars that vary by pulsating. The RVB stars are characterized by long supercycles where the mean magnitude drops by a magnitude or more while the star maintains its underlying...
October 28, 2011 - 8:03am
S Cas is a well-observed Mira variable of the northern skies with a longer-than-average period over 600 days. It currently has a range of over eight magnitudes, although that seems to have varied in the past; as recently as the 1970s S Cas seemed to have a series of faint maxima where...
July 16, 2012 - 8:22am
S Cephei is a highly evolved carbon-type Mira variable with a period of about 485 days. S Cep exhibits the large amplitude pulsations typical of Miras, but there is more irregularity present in the light curve than usual. The shape and amplitude of each cycle vary from one to the...
September 10, 2012 - 1:49pm
S Pav is a bright southern semiregular with a primary pulsation period near 400 days. Over extended periods of time, the light curve shows clear evidence of variations in the light curve that may be due to secondary pulsation modes. When multiple periods are present in a light...
August 30, 2010 - 1:35pm
S Persei is one of the supergiant semiregular pulsating variables of type SRc. These luminous stars, supergiants of the upper HR diagram, undergo a variety of different behaviors all caused by pulsation of one kind or another. Some, like Betelgeuse, vary inconspicuously by no more...
April 19, 2011 - 11:01am
S Serpentis is a fine example of a Mira variable with a bump in its light curve. There are a number of Miras that show cycle-to-cycle variations in their light curves, and such variability is more common than not among the Mira class of stars. The reasons why bumps or secondary...
December 2, 2011 - 11:08am
Supernova 2011fe was detected in late August 2011 in the nearby galaxy M101, and has put on a beautiful show for northern skywatchers since. SN 2011fe is a type-Ia supernova, which originate from accreting white dwarfs in binary star systems. When the white dwarf reaches a critical...
July 18, 2010 - 12:28pm
SS Cygni is a dwarf nova -- a binary star system composed of a normal sunlike-star transferring matter onto a white dwarf companion star. The matter being transferred forms an accretion disk around the white dwarf, and this disk sometimes goes into outburst, becoming hot and bright for a...
January 31, 2012 - 3:11pm
SS Gem is a bright example of the RV Tauri class, and more specifically of the RVa subclass whose mean brightness remains relatively constant. (The RVb class, of which a star like U Mon is an example, are characterized by long-period changes in brightness.) They're...
May 4, 2012 - 12:08pm
SS Vir is a semiregular variable with an "inconvenient" period of 361 days, which is close enough to one year that we cover nearly the same phase range year after year. This makes it challenging to understand the light curve without lots of data. To make things even more...
December 6, 2011 - 1:34pm
SU Tau is a well-observed R Coronae Borealis star. Like the prototype of the class, SU Tau undergoes very dramatic fadings of several magnitudes that occur seemingly at random; the star may remain constant between 9th and 10th magnitude for several years, and then exhibit wild drops in...
March 18, 2011 - 1:51pm
SX Herculis is a fine, bright semiregular variable with a period around 100 days. Its light curve isn't too irregular, but it's clear that it undergoes changes in amplitude over time. It is one of the prototypical SRd variables, classified by the GCVS as yellow...
April 19, 2011 - 1:27pm
SY Muscae is the first of three symbiotic stars we'll highlight over the next few weeks. SY Mus is a fine southern Z Andromedae variable although we have yet to observe any outbursts of this star. It does however show the familiar wave-like variation in the light curve. ...
November 6, 2012 - 12:33pm
SY Persei is a semiregular variable (SRa subclass) of long period, over 450 days. It undergoes reasonably regular pulsations, varying between 8.5 and 13.5, but the light curve varies enough from cycle to cycle to put it in the semiregular (rather than Mira) class of variables. It...
November 13, 2011 - 3:51pm
T Cas is a northern Mira with what appear to be traveling waves in the light curve. If you look at the maxima over the last several thousand days, you'll see that there appear to be multiple peaks that shift in time from cycle to cycle. The depth of the minima appear to change...
August 3, 2012 - 12:21pm
T Cen is a bright southern RV Tauri variable, ranging from m(vis) of 5.5 to 9th magnitude. Successive minima are separated by just under 100 days, but since the minima alternate, the true period is about 190 days. The RV Tauri stars are highly evolved giant stars that vary due to...
October 22, 2010 - 9:51am
T Monocerotis is a bright pulsating variable star belonging to the class of Cepheid variables. The Cepheids are variables that undergo self-sustaining, spherically symmetric pulsations with periods of days to weeks. They have long played an important role in astrophysics,...
