Astronomy

Spectral Class Breakdown

Spectral Class Breakdown

Where can I get a more detailed breakdown of Spectral Classes. Wikipedia only has it at Letter level rather than sublevel.

For example, https://en.wikipedia.org/wiki/Stellar_classification has B ranging from 10,000 - 30,000K. B0 is different to a B9, what would be the temperature range for a B0 or a B9 but not limiting to B but for all letters?

I'm not just looking at Temperature, I'm after Mass, Radius, Luminosity, Hydrogen Lines etc.

The closest that I've come is https://sites.uni.edu/morgans/astro/course/Notes/section2/spectraltemps.html but it doesn't mention types II or IV and doesn't have Radius or Mass.


Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2004 April 18
Stellar Spectral Types: OBAFGKM
Credit & Copyright: KPNO 0.9-m Telescope, AURA, NOAO, NSF

Explanation: Astronomers divide stars into different spectral types. First started in the 1800s, the spectral type was originally meant to classify the strength of hydrogen absorption lines. A few types that best describe the temperature of the star remain in use today. The seven main spectral types OBAFGKM are shown above with the spectrum of a single "O" star at the top followed by two spectra each from the progressively cooler designations, respectively. Historically, these letters have been remembered with the mnemonic "Oh Be A Fine Girl/Guy Kiss Me." Frequent classroom contests, however, have come up with other more/less politically correct mnemonics such as "Oven Baked Apples From Grandpa's/Grandma's Kitchen. Mmmm." Our Sun has spectral type "G".


IY Comae Berenices Spectral Class

One of their representatives has replied to an email I sent, which my wife translated into French, and has stated that IY Comae Berenices ought to be considered as having a spectral class of K9.

One of the Cloudy Nights contributors called Mwr stated that this same star with the designation HD 108815 as having a spectral class of K9 also. He provided a link from December 2012 from adsabs.harvard.edu which gave that precise spectral class. Therefore I now congratulate Mwr for providing with this ultimate truth.

I now believe that the AAVSO people are not correct in saying that IY Com has a spectral class of M2.
Sorry about that!

It's clear to me they need to correct themselves and to agree with both Simbad and adsabs.harvard.edu. on K9.

My Guide 9.1 DVD simply agrees with AAVSO when they say IY Com is M2 also. Project Pluto is very often quoting from AAVSO on its program.

K9 stars must be very rare. There must be precious little difference between K9 and M0 in spectral class.

I don't believe I have ever observed a K8 or a K9 star. Stars whose spectral class is K7 I certainly have observed alright.

Therefore IY Com is the only such spectral class of K9 I have ever observed.

In closing, if anyone now visits the Basic Query link on Simbad, they will see the welcoming sight of seeing IY Com as a K9 star. It most certainly is not a carbon star. It's an orange star and a very good one at that.

I have observed it a number of times and I must say I greatly admire its colour with my William Optics 158 mm F/7 apochromatic refractor. And I will do so again during Spring 2021. It is very close to the double star 24 Comae Berenices which is another beauty because of its colours.


The Milky Way Galaxy.

In class we were talking about the milky way galaxy, not necessarily all the planets found in it, but more or less the size shape and structure of the milky way itself. There are millions of stars in it and while with the naked human eye we can only see hundreds or thousands, but with the power of a scope we can see all those millions! To get the size and shape of the milky way astronomers will measure the distance to globular clusters. On the other hand when we are trying to figure out the mass of the milky way itself, astronomers turn to the orbit of said clusters to again get an accurate estimate of the mass. The milky way is centered around its bright and massive galactic nucleus.

Using the tutorial on pages 135 to 138 of the workbook we were able to do some galactic measuring of our own! For instance on page 135 we need to use the picture provided to us on the bottom of the page to approximate the distance of the sun to the center of the milky way. Using the scale of 1 centimeter representing 10,000 light years, we were able to determine that the sun is 3 centimeters away from the center of the galaxy in the photo, making it about 30,000 light years way from the center in reality. On the following pages we used our knowledge of knowing that the milky way galaxy is 100,000 light years across to see if various items on the tables provided on pages 136 and 137 were actually in fact part of our galaxy or not.

While our focus being on the milky way galaxy, it made this article a prime candidate for us, because it too focused on the milky way galaxy. The article was about how astronomers have actually discovered well over a 150 globular clusters in the milky way galaxy, especially around its “halo”. I found it interesting that astronomers took note in this one specific cluster, even though they use all of them in determining the size, shape, and mass of the milky way galaxy. The reason this one stood out specifically is because it happened to be oddly far brighter than all the others. Astronomers have thought this to be another galaxy that just accidentally got a little to close and got ripped to shreds by the gravity of the milky way galaxy.

This section answered a lot of questions I had in regards to astronomy if I’m being honest. I had a hard time understanding certain things about astronomy as to how someone can measure and weigh out the entire galaxy! Its very reassuring to know that there is an actual method behind it all and that the information we are being provided in regards to our galaxy is accurate!


A final project paper on a topic chosen from a list of suggested topics will be due at the end of the semester. This will be an individual assignment. Detailed instructions and rubrics for this will be posted on Blackboard at the appropriate time.

Since this approach for collaborative work is tried for the first time, it is an experimental approach. For this reason, there may be changes to the format during the semester based on student feedback on what works and what needs to be modified.

ACADEMIC HONESTY FOR COLLABORATIVE WORK

Academic honesty policies apply for all the work you do in this category as well. Although you will be using a web-based planetarium software and other simulations for these activities, you must not get the data directly from the internet or any other source outside of what is indicated in the activity write-up.

Doing so will earn a grade of zero (0) for the work. If you are not clear about what is and what is not allowed for a specific activity, check with me first. &ldquoI did not know it was not allowed&rdquo is not a valid excuse.


Spectral classification

How can we use stellar spectra to determine the properties of stars? What's the connection between spectral features and temperature, or chemical composition, or density? Let's start by putting different spectra into groups, so that we face only ten or twenty classes instead of thousands of individual stars.

The Harvard classification system

Thanks to a generous donation from the estate of Henry Draper, the Harvard College Observatory acquired the world's largest collection of stellar spectra in the late nineteenth and early twentieth century. Few male scientists would pore over the thousands of tiny spectra with microscopes on hundreds of glass plates it was too boring and didn't pay enough. The job of recording, measuring, and classifying this wealth of information was given to a group of female scientists, led by Annie Jump Cannon and Williamina Fleming.

Fleming decided to use the absorption lines of hydrogen to place spectra into different classes. She called the spectra with the strongest lines "A", the next strongest "B", and worked her way down the alphabet to "O", where the lines were virtually invisible. Here's a small selection of spectra shown in that order:

Cannon noticed that this arrangement ALMOST put stars in order by temperature -- -- as measured by the continuum of the spectrum, and by photometric colors. With just a few changes (getting rid of some intermediate classes, and shifting the O class to the top of the list), Cannon created a true temperature sequence that has since been used as the primary means of classifying stars.

The result of decades of hard work by the Harvard astronomers was the Henry Draper Catalogue and Extension , which contains classifications for over 270,000 stars.

Exercise: Classify the star below, using the rules shown in the charts above (and the rules in Table 8.1 of your textbook). First, a view of the entire spectrum in the blue:

Now, a closeup of the region between 4000 and 4400 Angstroms.

Equivalent width

Okay, so we can place stellar spectra into classes, which have something to do with the temperature of their outer layers. Fine. But what about the abundances of different chemical elements? How is chemical composition related to the strength of absorption lines?

  • if we see a line of hydrogen, does that mean that the star contains hydrogen?
  • if we DON'T see a line of hydrogen, does that mean that the star DOESN'T contain hydrogen?
  • if we do see an absorption line of hydrogen, how much hydrogen must there be in the photosphere?
  • if a line due to hydrogen is stronger than one due to iron, does that mean there are more H than Fe atoms in the photosphere?

Good questions. In order to address them, we need a quantitative measure of the "strength" of an absorption line. Astronomers have chosen a quantity called equivalent width to describe absorption lines. If we plot intensity versus wavelength in the standard manner,

then we can measure the "strength" of a line by measuring the "area under the curve". The top of the area is supposed to be the level of the surrounding continuum, but it can be hard to find the continuum in some cases. This one isn't so bad.

Now, the equivalent width of a line is simply the width of a perfectly rectangular line of the SAME AREA which would run from the continuum all the way down to zero (that is, no light at all). This line has an equivalent width of about 10 Angstroms, it would seem.

  1. What is the equivalent width of the line near 4225 Angstroms?
  2. What element produces this line?

Using spectra to determine composition: Round One

Right. The Henry Draper project provided an enormous number of stellar spectra and a rough classification for each. As telescopes grew larger and larger, astronomers could take more and more detailed spectra, with higher and higher signal to noise. It was soon possible to measure very precisely the strengths of many different lines in a number of stars. The question was -- how were the lines connected to abundances?

Consider the following two small sections of spectra: one from the star Vega, one from the star 104 Tau (the spectrum of which is very similar to that of the Sun).

  1. Measure the equivalent widths for the (3 to 5) strongest lines in the spectrum of each star.
  2. Identify the element responsible for each of these strong lines.
  3. Using equivalent width as a proxy for abundance, calculate the relative abundances for the most common elements in each star.

For more information

    An Atlas of Stellar Spectra describes a later extension of the Harvard system. It provides details on how one should examine low-dispersion stellar spectra to classify them.

Copyright © Michael Richmond. This work is licensed under a Creative Commons License.


The Yerkes Spectral Classification

The Harvard classification only takes into account the effect of the temperature on the spectrum. For a more precise classification, one also has to take into account the luminosity of the star, since two stars with the same effective temperature may have widely different luminosities. A two-dimensional system of spectral classification was introduced by William W. Morgan, Philip C. Keenan and Edith Kellman of Yerkes Observatory. This system is known as the MKK or Yerkes classification. (The MK classification is a modified, later version.) The MKK classification is based on the visual scrutiny of slit spectra with a dispersion of 11.5 nm/mm. It is carefully defined on the basis of standard stars and the specification of luminosity criteria. Six different luminosity classes are distinguished:

- Ia most luminous supergiants,

- Ib less luminous supergiants,

- V main sequence stars (dwarfs).

The luminosity class is determined from spectral lines that depend strongly on the stellar surface gravity, which is closely related to the luminosity. The masses of giants and dwarfs are roughly similar, but the radii of giants are much larger than those of dwarfs. Therefore the gravitational acceleration g = GM/R2 at the surface of a giant is much smaller than for a dwarf. In consequence, the gas density and pressure in the atmosphere of a giant is much smaller. This gives rise to luminosity effects in the stellar spectrum, which can be used to distinguish between stars of different luminosities.

1. For spectral types B-F, the lines of neutral hydrogen are deeper and narrower for stars of higher luminosities. The reason for this is that the metal ions give rise to a fluctuating electric field near the hydrogen atoms. This field leads to shifts in the hydrogen energy levels (the Stark effect), appearing as a broadening of the lines. The effect becomes stronger as the density increases. Thus the hydrogen lines are narrow in absolutely bright stars, and become broader in main sequence stars and even more so in white dwarfs (Fig. 8.6).

2. The lines from ionized elements are relatively stronger in high-luminosity stars. This is because the higher density makes it easier for electrons and ions to recombine to neutral atoms. On the other hand, the

Fig. 8.6. Luminosity effects in the hydrogen Hy line in A stars. The vertical axis gives the normalized intensity. HD 223385 (upper left) is an A2 supergiant, where the line is very weak, 0 Aurigae A is a giant star and a2 Geminorum is a main sequence star, where the line is very broad. [Aller, L.H. (1953): Astrophysics. The Atmospheres of the Sun and Stars (The Ronald Press Company, New York) p. 318]

Fig. 8.6. Luminosity effects in the hydrogen Hy line in A stars. The vertical axis gives the normalized intensity. HD 223385 (upper left) is an A2 supergiant, where the line is very weak, 0 Aurigae A is a giant star and a2 Geminorum is a main sequence star, where the line is very broad. [Aller, L.H. (1953): Astrophysics. The Atmospheres of the Sun and Stars (The Ronald Press Company, New York) p. 318]

rate of ionization is essentially determined by the radiation field, and is not appreciably affected by the gas density. Thus a given radiation field can maintain a higher degree of ionization in stars with more extended atmospheres. For example, in the spectral classes F-G, the relative strengths of the ionized strontium (SrII) and neutral iron (FeI) lines can be used as a luminosity indicator. Both lines depend on the temperature in roughly the same way, but the Sr II lines become relatively much stronger as the luminosity increases.

3. Giant stars are redder than dwarfs of the same spectral type. The spectral type is determined from the strengths of spectral lines, including ion lines. Since these are stronger in giants, a giant will be cooler, and thus also redder, than a dwarf of the same spectral type.

4. There is a strong cyanogen (CN) absorption band in the spectra of giant stars, which is almost totally absent in dwarfs. This is partly a temperature effect, since the cooler atmospheres of giants are more suitable for the formation of cyanogen.


Boondock Camping and Astronomy

I live in Reno and own a GMC2500HD truck with Leer shell and an Artic Fox 22G that we bought about 2 years ago to support astronomy camping. I have the trailer setup to be power independent with 1405 wats of solar, 400 amp-hours of LiFePO4 batteries and 2200 watt inverter that can run the 11000 power saver air conditioner as long as the sun is up.

We have been going on my astronomy related vacations to star parties or just adventures to places like southern Utah or Death Valley. We really enjoy Bortle 1 skies and observing in the Reno light pollution just doesn't do much for us anymore.

I have been brainstorming lately regarding exploring with my truck without the trailer to find places that are about 60 miles by pavement and another 3-5 miles of unpaved roads to BLM or Forest Service land with extremely dark skies and dispersed camping. I have a mattress that fits in the truck shell and we can take a scope or two to enjoy the sky overnight when exploring. Once we have picked out the sites with just the truck we would return in the future with our trailer. The summer location would need to be higher to avoid the daytime heat so we could enjoy taking hikes. The cooler season locations could be anywhere it is dark and the roads are reliable enough not to be stuck in sand or mud if it rains.

My goal to be able to do a 2 night astronomy trip with my wife and dog at least once a month during the 7-8 months when it isn't too cold to worry about freezing. I prefer not to go to campgrounds because the other campers may bring light pollution with them.

I have a Garmin InReach satellite messenger to reach out for help if we completely got stuck or broken down. Most of the places I am considering are totally away from cellular coverage.

Anybody else how lives out west have their favorite boon docking astronomy camping destinations that are close enough to home to become frequent weekend trips?


Day-By-Day Classroom Breakdown – Ecology and Ecosystems

A great video by ASAP Science that looks at what would happen to our entire infrastructure if humans left earth. I use this video to start my unit on ecology which focuses on the sustainability of ecosystems.

– I followed my discussion with a quick introduction on my Ecology Unit. Click here to have a look at what I’ll be covering.

– I love the story – The Lorax by Dr. Suess. Following my introduction to ecology, I got my kids to research when The Lorax was written (1971). I told them how its story was so far ahead of its time. When it was published there was no discussion of Global Warming and very few people concerned themselves with the environment like they do today. I show my students The Lorax movie which can be found here which they would use to complete their Lorax Assignment. Most of the work is done following the movie, but they can fill in some information while the video was playing. The video can be found BY CLICKING HERE.

– This isn’t a huge assignment, but it gets them thinking.

Homework: Students have their Lorax Assignment due in 3 days and their Senses Lab due in 4 days.

Class starter – A minds-on fun science video to get them focused and thinking science – The Science Of Laziness

So many kids label themselves as “lazy” but do they know what lazy is? What causes it? A great video by ASAP Science that looks the science behind laziness.

– Started the day by watching (and filling in the worksheet for) Bill Nye – Atmosphere

Class starter – A minds-on fun science video to get them focused and thinking science – Lesson 2 – Ecosystems

– Starting in 2 days, we will begin our Ecobottle Inquiry Lab . This lab allows your students to create and carry out a hands-on, engaging experiment on how humans affect our environment. It utilizes the steps in the scientific method to scaffold learning and allow your students to come to a conclusion based on findings that are tangible and really complements what we’ve done so far this year. I reminded them that they need to bring in their empty water bottles so we can get started soon.

Homework: Students have their Lorax Assignment due in 2 days and their Senses Lab due in 3 days

Class starter – A minds-on fun science video to get them focused and thinking science. Today I wanted to show my kids the Magnus Effect. Nothing in-depth at all, just some cool science that explains why flying objects curve when they are spin. First we watch – The Physics of the “Impossible” Free Kick then a really good video which shows the effects on a large scale – The Magnus Effect Example.

– I collected The Lorax Assignment

– In keeping with our lesson yesterday on Lesson 2 – Ecosystems , I took my students out for a walk to our nearby park to collect data on Biotic and Abiotic factors they could find. As well, they were asked to document human influence. The worksheet they were asked to fill in can be foud here – Ecology Walk Worksheet

Homework: Students have their Senses Lab due next day.

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – How do ants take care of their farms?

– Class started by introducing their Ecobottle Lab which will run through the rest of the unit. This ecosystems lab allows your students to create and carry out a hands-on, engaging experiment on how humans affect our environment. It utilizes the steps in the scientific method to scaffold learning and allow your students to come to a conclusion based on findings that are tangible.

– We then covered the rest of day 1 for Lesson 3 – Energy Flow in Ecosystems

– For the last few minutes of class, I let them get started on their homework which was to create a Venn diagram comparing Photosynthesis and Cellular Respiration.

Homework: Venn diagram comparing Photosynthesis and Cellular Respiration. This will be due in 3 days.

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – How Big Is The Ocean?

**Note: For the Ecobottle Lab, each day following the video, students water their plants**

– We then watched and completed a worksheet for: Bill Nye Food Web

Homework: Venn diagram comparing Photosynthesis and Cellular Respiration. This will be due in 2 days.

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – What Causes Pins and Needles?

– I loved today’s lesson because I had my students complete an in-class, inquiry task on Food Webs. You can download the activity by clicking –> Food Web activity . They had 50 minutes in class to complete it and had to submit it prior to the end of the period. I really like this activity because it brings some real-world application to our Ecology Unit .

Homework: Venn diagram comparing Photosynthesis and Cellular Respiration. This will be due in next day.

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – The 6 Craziest Mass Extinctions

– Started by taking up the Food Web activity as a class.

– Lastly, we started Lesson 4 – Cycling of Matter in Ecosystems , but only got through a few slides.

Homework: Venn diagram comparing Photosynthesis and Cellular Respiration. This will be due next day.

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – The 5 Myths About Sugar .

– First up, I collected the Venn Diagram Assignment

– We continued with Lesson 4 – Cycling of Matter in Ecosystems , getting through the remainder of the Water Cycle. I then introduced our Water Cycle assignment which can be Found Here .

Homework: Students were to complete the Water Cycle assignment and return it next day.

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – Can Earbuds Lead to Hearing Loss?

– We started with a peer evaluation of the Water Cycle Diagram I gave last day.

– We finished Lesson 4 – Cycling of Matter in Ecosystems , getting through the remainder of the Cycles. I then introduced our Carbon Cycle Diagram assignment which we will work on next day.

Homework: No homework tonight.

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – Does My Voice Really Sound Like That? I know when I hear a recording of my voice, it sounds like an entirely different person. The students can appreciate this because it happens to them also.

– We started by adding our “human factor” to our Ecobottle Lab.

– The remainder of the class was dedicated to starting our Carbon Cycle Diagram assignment which will be due in 4 days.

Homework: Carbon Cycle Diagram assignment due in 3 days.

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – Why Do Paper Cuts Hurt So Much?

– For the latter half of the class, I gave out my Deer Population Case Study which looks at how populations fluctuate due environmental factors such as number of predators, food availability, etc.

– Deer Population Case Study assignment due in 2 days.

– Carbon Cycle Diagram assignment due in 2 days.

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – Why Do Zebras Have Stripes?

– The day started by having the students add their human factor to their Ecobottle Lab.

– Ecology Unit Test in 3 Days

Class starter – A minds-on fun science video to get them focused and thinking science. Today I showed my kids – Talent vs. Training and how genetics as well as effort, contributes to someone’s ability level.

– Today we covered two lessons:

– Ecology Unit Test in 2 Days

– With all the lessons complete, today is for review and the way I review is by doing my Ecology Task Card game. This Ecology Task Card resource is very unique. I use it as a clue gathering, puzzle solving, highly active and engaging review activity. What I love to do is have the kids go through the activity for the first half or two-thirds of our review period then spend the remainder of the time reviewing the questions as a class on the overhead projector.

– Study for the Ecology Unit Test

Ecology Unit Test Day. The test can be found within my Ecology Unit.

I hope you have enjoyed my tour through the Ecology Unit. Please click below to visit the different units I’ve posted.