Now that you have explored the relationship between spectral type, temperature and luminosity, you can further investigate these variables using with the simple animation at the bottom of the website:

http://astro.unl.edu/naap/hr/hr_background1.html

To check for understanding, use the slider bar to answer the following questions below  .  Answers may be submitted as a text entry or file attachment.

What are the surface temperatures and colors of:

· a hot O2 star?   __________________________

· a cool M3 red dwarf?______________________________

· a G2 star like the sun? _________________________

What is the spectral type of a star with:

· a surface temperature of 10,000 K ?  ______________________

· a surface temperature of 5,000 K ?  _________________________

What is the color of a star with:

· spectral type A0?   __________________________________

I. MAIN VARIABILITY GROUPS

A first distinction has to do with the nature of the variations:
Extrinsic
Variability is due to eclipse of one star by another or the effect of stellar rotation
Extrinsic variable stars are divided into three groups:
Eclipsing
Orbital plane coincident with our line of sight
Rotating
Spots, reflection, or ellipsoidal shape
Microlensing events

Intrinsic
Variation is due to physical changes in the star or stellar system

Intrinsic variable stars are divided into four groups:
Pulsating
Contraction and expansion
Eruptive
Mass ejection or chromospheric activity
Cataclysmic
Interacting binary systems with white dwarfs or stars showing large amplitude outbursts
X-ray
Binary systems with neutron stars or black holes

II. VARIABLE TYPES WITHIN MAIN GROUPS

1. ECLIPSING
Main types
E
Eclipsing binary systems. These are binary systems with orbital planes so close to the observer’s line of sight (the inclination of the orbital plane to the plane orthogonal to the line of sight is close to 90 deg.) that the components periodically eclipse each other. Consequently, the observer finds changes of the apparent combined brightness of the system with the period coincident with that of the components’ orbital motion.

EA
β Persei-type (Algol) eclipsing systems. Binaries with spherical or slightly ellipsoidal components. It is possible to specify, for their light curves, the moments of the beginning and end of the eclipses. Between eclipses the light remains almost constant or varies insignificantly because of reflection effects, slight ellipsoidality of the components, or physical variations. Secondary minima may be absent. An extremely wide range of periods is observed, from 0.2 to ≥10000 days. Light amplitudes are also quite different and may reach several magnitudes.

EB
β Lyrae-type eclipsing systems. These are eclipsing systems having ellipsoidal components and light curves for which it is impossible to specify the exact times of onset and end of eclipses because of a continuous change of the system’s apparent combined brightness between eclipses; secondary minimum is observed in all cases, its depth usually being considerably smaller than that of the primary minimum; periods are mainly longer than 0.5 days. The components generally belong to early spectral types (B-A). Light amplitudes are usually <2 mag. in V.

EP
Stars showing eclipses by their planets.
Prototype: V376 Peg.

EW
W Ursae Majoris-type eclipsing variables. These are eclipsers with periods usually shorter than 1 day, consisting of ellipsoidal components almost in contact and having light curves for which it is impossible to specify the exact times of onset and end of eclipses. The depths of the primary and secondary minima are almost equal or differ insignificantly. Light amplitudes are usually <0.8 mag. in V. The components generally belong to spectral types F-G and later.

Survey types
EC
Contact binaries in ASAS-3. Both components filling or close to filling their Roche lobes. These are mostly EW variables.

ED
Detached eclipsing binaries (EA) in ASAS-3.

ESD
Semi-detached eclipsing binaries (EA or EB) in ASAS-3.

Subtypes
AR
Detached systems of the AR Lacertae type. Both components are subgiants not filling their inner equipotential surfaces.

D
Detached systems, with components not filling their inner Roche lobes.

DM
Detached main-sequence systems. Both components are main-sequence stars and do not fill their inner Roche lobes.

DS
Detached systems with a subgiant. The subgiant also does not fill its inner critical surface.

DW
Systems similar to W UMa systems in physical properties (KW), but not in contact.

EL
EL CVn-type binaries, consisting of a core helium-composition pre-white dwarf and an early-type main-sequence companion.

GS
Systems with one or both giant and supergiant components; one of the components may be a main sequence star.

ORDER NOW FOR AN ORIGINAL PAPER!!! Variables of Spectral type/temperature/ luminosity

ADDITIONAL INSTRUCTIONS FOR THE CLASS

Discussion Questions (DQ)

• Initial responses to the DQ should address all components of the questions asked, including a minimum of one scholarly source, and be at least 250 words.
• Successful responses are substantive (i.e., add something new to the discussion, engage others in the discussion, well-developed idea) and include at least one scholarly source.
• One or two-sentence responses, simple statements of agreement, or “good post,” and responses that are off-topic will not count as substantive. Substantive responses should be at least 150 words.
• I encourage you to incorporate the readings from the week (as applicable) into your responses.

Weekly Participation

• Your initial responses to the mandatory DQ do not count toward participation and are graded separately.
• In addition to the DQ responses, you must post at least one reply to peers (or me) on three separate days, for a total of three replies.
• Participation posts do not require a scholarly source/citation (unless you cite someone else’s work).
• Part of your weekly participation includes viewing the weekly announcement and attesting to watching it in the comments. These announcements are made to ensure you understand everything that is due during the week.

APA Format and Writing Quality

• Familiarize yourself with APA format and practice using it correctly. It is used for most writing assignments for your degree. Visit the Writing Center in the Student Success Center, under the Resources tab in LoudCloud for APA paper templates, citation examples, tips, etc. Points will be deducted for poor use of APA format or absence of APA format (if required).
• Cite all sources of information! When in doubt, cite the source. Paraphrasing also requires a citation.
• I highly recommend using the APA Publication Manual, 6th edition.

Use of Direct Quotes

• I discourage overutilization of direct quotes in DQs and assignments at the Masters’s level and deduct points accordingly.
• As Masters’s level students, it is important that you be able to critically analyze and interpret information from journal articles and other resources. Simply restating someone else’s words does not demonstrate an understanding of the content or critical analysis of the content.
• It is best to paraphrase content and cite your source.

 

LopesWrite Policy

• For assignments that need to be submitted to LopesWrite, please be sure you have received your report and Similarity Index (SI) percentage BEFORE you do a “final submit” to me.
• Once you have received your report, please review it. This report will show you grammatical, punctuation, and spelling errors that can easily be fixed. Take the extra few minutes to review instead of getting counted off for these mistakes.
• Review your similarities. Did you forget to cite something? Did you not paraphrase well enough? Is your paper made up of someone else’s thoughts more than your own?
• Visit the Writing Center in the Student Success Center, under the Resources tab in LoudCloud for tips on improving your paper and SI score.

Late Policy

• The university’s policy on late assignments is 10% penalty PER DAY LATE. This also applies to late DQ replies.
• Please communicate with me if you anticipate having to submit an assignment late. I am happy to be flexible, with advance notice. We may be able to work out an extension based on extenuating circumstances.
• If you do not communicate with me before submitting an assignment late, the GCU late policy will be in effect.
• I do not accept assignments that are two or more weeks late unless we have worked out an extension.
• As per policy, no assignments are accepted after the last day of class. Any assignment submitted after midnight on the last day of class will not be accepted for grading.

Communication

• Communication is so very important. There are multiple ways to communicate with me: 
  • Questions to Instructor Forum: This is a great place to ask course content or assignment questions. If you have a question, there is a good chance one of your peers does as well. This is a public forum for the class.
  • Individual Forum: This is a private forum to ask me questions or send me messages. This will be checked at least once every 24 hours.