Observation of Specific Objects

Introduction

Astronomy from Home has its own robotic telescope, called GORT. Since 2004, GORT has been used to take digital photographs of parts of the night sky that contain stars that vary in brightness over time. These stars are called variable stars. When planets orbit a star other than our own Sun, they are called exoplanets. Sometimes exoplanets are large enough that they can make a star appear to be variable, since exoplanets can block some of the starlight. Both variable stars and exoplanet systems can be successfully observed using robotic telescopes, leading to important scientific results.

Astronomers refer to digital photographs from telescopes as images. To analyze image data, astronomers use a file format called FITS (Flexible Image Transport System). FITS files include information that is useful to the analysis, such as the pointing direction of the telescope and the time the image data were acquired. After downloading GORT or MicroObservatory data, there are several software packages that you can use to analyze the FITS files.

To start analyzing image data in FITS files, go to the MicroObservatory Analysis page and drag the file from your computer into the Js9-4L online software program. Follow the instructions on that site for analyzing the image. To learn how to determine the brightness of specific objects in an image, go to Astronomy from Home Discover page This page has links to analysis examples for different types of objects.

Exoplanet Transits

When an exoplanet passes in front of a star, the brightness of the star decreases. This dip in brightness is called an exoplanet transit. If you continue to observe the star, another dip in brightness will be seen when the exoplanet has completed its orbit around the star. Continued timing of exoplanet transits, therefore, allows precise orbital periods to be determined. In addition, by measuring the depth of the dip in brightness and knowing the size of the star, the size or radius of the planet can be determined. Variations in transit times or multiple dips indicate the possible presence of additional orbiting planets in the system. To learn more about exoplanet light curves, see Discover Exoplanet.



Diagram depicting the transit method of exoplanet detection. A planet is shown traversing a star, with the corresponding light intensity graph below.
Exoplanets detected by observing dips in the brightness of stars
Credit: NASA Ames Research Center

To see all exoplanets in the GORT image archive, visit the exoplanet archive page.

Eclipsing Binary Systems (EBs)

Eclipsing binary star systems consist of two stars in mutual orbit around their center of gravity. Depending on the size of the binary system, EBs can have orbital periods ranging from a few hours to several decades. However, most of the known eclipsing systems have periods of a few days, which is most likely due to the difficulty in finding longer period systems. As in transiting exoplanet systems, the light can be dimmed if a smaller star blocks some of the light from the larger, brighter star. Unlike exoplanet systems, however, both stars emit light so the resulting lightcurves can be complicated. Basic research activities involve measuring precise times of occurrence for eclipses and the depths of the eclipses. A detailed and complete light curve can used to determine the sizes of the stars in the system, as well as the tilt of the orbital plane with respect to an observer on Earth. The figure illustrates the eclipses seen in the Kepler 16 system, which consists of two stars that are each smaller than our Sun. This system also contains at least one exoplanet.

Image from Wiki Commons. Diagram of eclipsing binary stars, shown with corresponding light curve.
Eclipsing binary star Kepler 16 light curve Image Credit


To see all eclipsing binaries in the GORT image archive, visit the eclipsing binary archive page.

Supernovae

Supernovae (SNs) are produced in many different ways as stars evolve. In all cases, an extremely bright outburst is observed, which declines over many weeks – months as the explosion propagates outward, creating a supernova remnant. Type II supernovae are the result of massive stars exploding when they run out of nuclear fuel. Type 1a supernovae result from collapsing white dwarf stars which have gotten too heavy to sustain nuclear burning. To learn more about supernova light curves, and how they can be used to measure the expansion of the Universe, see Discover Supernova.

Image from Wiki Commons. Type 1a supernova remnant G299 as seen in X-ray light by NASA’s Chandra Observatory, superimposed on an infrared image of background stars.
Type 1a supernova remnant G299 as seen in X-ray light by NASA’s Chandra Observatory, superimposed on an infrared image of background stars.
Credit: X-ray: NASA/CXC/U.Texas/S.Post et al, Infrared: 2MASS/UMass/IPAC-Caltech/NASA/NSF

Unusual stars with outbursts or other unpredictable activity

Monitor stars with known unpredictable activity. (note: Professional observatories generally do not allocate observing time for such observations.) Normally such stars are quiescent and not active. These stars should be monitored because such events are unpredictable. When such events occur, the astronomical community should be notified so specialized instrumentation at professional facilities can be used to study these events.

Stars with unpredictable activity:

Cataclysmic variables (CVs)

  • Dwarf novae
  • Recurrent novae
  • Novae
  • Polars

RCB stars (inverse novae)

YSOs (Young Stellar Objects)

Variable nebulae (likely illuminated by YSOs)

SR stars (semi-regular variables)

Supernovae

Follow the decline of a supernova. Supernovae (SNs) are classified as cataclysmic variables, but the outburst is far brighter than other forms of CVs.

Cepheids


Before the discovery of Cepheid variable stars, there was no way to accurately measure the distance to objects outside of our own Milky Way Galaxy. As discovered by Henrietta Leavitt in 1907 (and now known as Leavitt’s Law), the pulsation period of a Cepheid star is related to its absolute brightness. Cepheids pulse in size (and therefore in brightness) in a very regular pattern, which takes longer to complete the bigger they are. Comparing the pulsation period (how long it takes for the star to brighten, dim and brighten again) to the Cepheid’s maximum observed brightness, allows a determination of the distance to the star. This is similar to estimating the distance to a streetlight on the highway – the farther away it is, the dimmer it looks. Astronomers used Cepheid variable stars to determine distances to galaxies for the first time, when no one really understood just how far away they were (or that some Cepheids were in neighboring galaxies). NASA’s Hubble Space Telescope still performs distance measurements using Cepheid stars today, in order to more precisely measure the expansion rate of the nearby Universe. Cepheids form the first rung of the cosmic distance ladder, connecting our galaxy to its nearest neighbors. Subsequent rungs on the ladder connect our local group of galaxies to others that are more distant, and in which we cannot measure individual Cepheids. To learn more about Cepheid light curves, see Discover Cepheid.

Cepheid light curve, repeating rise and falls in intensity. From Wikicommons.
Light curve of Cepheid variable V1 in our neighbor, the Andromeda galaxy. Red points denote data taken by amateur astronomers and stars indicate four observations by the Hubble Space Telescope.
CREDITS:
Illustration: NASA, ESA, and Z. Levay (STScI);
Science: NASA, ESA, the Hubble Heritage Team (STScI/AURA), and the American Association of Variable Star Observers;
Acknowledgment: T. Rector (University of Alaska, Anchorage)

To see all Cepheids in the GORT image archive, visit the Cepheid archive page.