Introduction to Authentic Research

What is authentic research and how is it done? We provide you with the information on where to start for making meaningful observations. If you are new to Authentic Research we hope this introduction gives you a basis on how to study what.

Astronomical Background

A belief long held by western civilization is that the cosmos is immutable and unchanging. Such views were discussed by Plato, Aristotle, and others. The notion of the Fixed Stars implied that the stars in the sky do not change their appearance. They do not change their positions with respect to other stars and do not change their brightness. Of course, we now know that both these notions are incorrect.

Stars do change their positions with respect to other stars. These changes are exceedingly small, but contemporary technology can detect these changes and can utilize these measurements to determine distances to the stars and to study the motions of stars as they orbit within our Milky Way galaxy. Furthermore, some stellar appearing objects do appear to be in constant motion. These are the so-called asteroids which can readily be shown to be part of our solar system and orbiting our sun like the major planets. And some stars do change their brightness with respect to other stars. These are the variable stars.

The sky is not unchanging. While over human time scales the stars seem unchanging, stars are born, they evolve and change throughout their lifetimes, and they die. Stars like the sun can seem constant and stable for long periods of time, but change is inevitable. Indeed, for certain types of stars, and for certain stages in the lifetime of a star the changes can be quite dramatic and can easily be seen and detected within human time scales.

We now realize there are actually many easily detectable variable stars. These are the stars that vary in brightness. In general, variable stars are stars in very special stages in their life cycles. Often times these are young stars, or old stars, or stars undergoing transitions from one stage or configuration to another. Stars like the sun often appear quite constant for long periods of time. However, even the sun is variable at very small levels and in various ways. Indeed, one could make the claim that all stars are variable stars if you can measure accurately enough and wait long enough. The number of officially designated variable stars now exceeds 40,000, but new variables are now being discovered at a rate approaching many hundreds each year. Technologies and programs now under development will soon be discovering variables at a rate of several thousand new variables each year.

Variable stars are most simply characterized in terms of the appearance of their light curve. A light curve is simply a plot of the brightness as a function of time. For many variable stars the light curve repeats its shape. These variables are periodic. Due to selection effects of the discovery process, most known variables with periods have periods of a few days. However, there are variables known with periods of hundreds of days and even some with periods of many years. There are also many variables with periods less than a day and even some with periods of a few minutes. Not all variables are periodic. Some appear to be exhibiting random variations, and exhibit activity which is not predictable in any way.

There are three basic types of variable stars: Pulsating variables, Eclipsing variables, and Explosive Variables. Pulsating variables vary in brightness because their internal structure is unstable to pulsation. They are like a bell that is ringing, or a string that is vibrating. Eclipsing variables are binary star systems with orbital planes which are aligned pointing toward our planetary system. They vary in brightness when one member of the binary eclipses the other member. Explosive variables detonate explosive events when they reach unstable stages in their life cycle.

All variable stars can be used to evaluate theories of stellar evolution. This is because all variable stars are in special stages of their life cycles. This is one of the ways we can compare our theories of stellar evolution with observations. There are also specific models for each of the types of variable stars that can be used to predict the changes in brightness. The observed variations in brightness can then be compared with theoretical predictions. Varying parameters in the models can often be used to determine physical characteristics for the stars by fitting the model calculations to the observed light curves. Light curves for which a model fit is not possible may indicate physical circumstances not considered in the models or may indicate the need for improvements in the models. This is how science works!

Pulsating variables can often be used to determine distances. This is because the periods of pulsation are often correlated with the intrinsic brightness, or luminosity, of the star. Thus, determining the period for the star then allows a computation of the intrinsic brightness which can then be compared with the observed brightness to determine the distance.

Binary star systems provide the only means of determining the masses for stars. This is extremely important since it is the mass of a star that determines the internal structure and the Evolution of the star. Eclipsing binary systems also provide the only means of determining the sizes for stars. Sizes are one of the parameters that can be determined by fitting models to light curves of eclipsing binaries. Other parameters include temperatures, luminosities, and especially the orbital inclination. Binary star systems provide us with the only means to make fundamental measurements of physical characteristics of stars. Fortunately, eclipsing binaries are known containing virtually all the various types of stars and stars in virtually all the possible stages of stellar evolution. This includes the hottest and most massive stars, the coolest and lowest mass stars as well as giants, supergiants, and white dwarfs. This includes stars just being formed out of the interstellar medium in stellar nurseries, and stars approaching the end of their lives. Eclipsing binaries provide us with excellent astrophysical laboratories for a wide range of areas in astrophysics.

Recommended background in astronomy and astrophysics

For the satisfactory completion of AfH research projects a familiarity with the following general concepts is advised. The AfH provides recommended reading and resources covering these concepts.

Coordinate systems and practical astronomy

• Longitude, latitude
• Azimuth, altitude
• Right ascension, declination, hour angle
• Rising and setting of objects in the sky
• Duration and variation of daylight and darkness
• The seasons

Time

• Standard time, daylight time
• Universal time
• Sidereal time
• Julian Date (JD)
• Heliocentric Julian (HJD)

Astronomical magnitudes

• Apparent magnitudes
• Colors and the color index
• Absolute magnitude

Spectral classification

• Spectral types of stars
• Luminosity classes of stars

The HR diagram

• Appearance of the diagram
• Different types of HR diagrams
• Stellar evolution

Variable stars

• Types of variable stars
• Light curve (plot of brightness versus time)
• Phase for a periodic variable
• Light elements (model for predicting events for a periodic variable)

Getting Started

In order to be successful with AfH research projects, any project participant will need to have familiarity and experience with the following types of activities. The AfH provides introductory activities and the guidance needed to obtain the necessary experience.

Determining if an object of interest or a region of the sky will be observable from the location of a designated telescope.

Determining if an object of interest is observable on a designated date.

Determining what time of night an object of interest can be observed.

• What time will the object be highest in the sky?
• What time will the object rise?
• What time will the object set?

Determine how to control the telescope and take images.

Telescope control software.

Camera control software.

OR

User interface to submit instructions for an autonomous robotic telescope.

How to identify objects of interest in an image.

Determine how to make brightness measurements, or determine astronomical magnitudes, for objects in an image.

Determine how to make positional measurements, or determine right ascension and declination, for objects in an image.

Suggested Research Projects

The AfH is committed to providing and supporting authentic research experiences in astronomy and astrophysics using computer-controlled telescopes and CCD imaging detectors. The projects recommended by the AfH will focus on photometry, or brightness measurements. Astrometry, or position measurements, will also be considered. Each project can produce authentic research, and can result in publishable results.