The Pleiades - Messier 45

The Pleiades are an open star cluster that is located in the constellation Taurus in the northern hemisphere. They are located at a mean distance of about 440 light years away from us and are part of our galaxy. With a mass of about 800 solar masses, they contain more than 1000 stars. Its age is roughly dated at around 125 million years. Estimates suggest that it will take another 125 million years until the gravitational bond will be to low to hold the star cluster together and the stars will drift away. It is assumed that the Pleiades may have originated from a star-forming area such as the Orion Nebula. Thus they could show how the Orion Nebula could evolve over the next million years.
Due to their high brightness and their expansion, they are already visible with the naked eye and are a popular target for (hobby)astronomers and astrophotographers. Depending on the visual strength of your eyes, up to seven stars can be recognized.

This picture is showing the Pleiades and was taken with a focal length of 420mm f6.5 from my backyard. It was also cropped to the region of interest. The total exposure time is 4.5 hours with subframes of 12x 5 minutes and 21x 10 minutes.

The brightest stars of the Pleiades

Copyright: NASA, ESA and AURA/Caltech; public domain

The picture above from the Hubble Space Telescope shows the brightest stars of the Pleiades with their names. The stars Asterope and Asterope II are summarized under the name Sterope, as it is a binary star system. Also, Taygeta is a double star system, it contains the stars 19 Tauri A and 19 Tauri B. The Luminosity in the table below is specified to be the x times the luminosity of our sun.

Star (Alt. name)	Visual brightness	Luminosity	Distance from Earth
Alcyone (25 Tauri)	2.85 mag	1,576.25 suns	403.17 Light Years
Atlas (27 Tauri)	3.62 mag	678.49 suns	382.37 Light Years
Electra (17 Tauri)	3.72 mag	803.19 suns	404.67 Light Years
Maia (20 Tauri)	3.87 mag	539.82 suns	383.27 Light Years
Merope (23 Tauri)	4.14 mag	399.91 suns	380.14 Light Years
[Taygeta] (19 Tauri A) (19 Tauri B)	4.30 mag	473.31 suns	409.24 Light Years
Pleione (28 Tauri)	5.05 mag	202.42 suns	381.92 Light Years
Celaeno (16 Tauri)	5.45 mag	109.62 suns	377.07 Light Years
[Sterope] Asterope (21 Tauri) Asterope II (22 Tauri)	5.76 mag 6.43 mag	81.77 suns 41.64 suns	371.91 Light Years 380.14 Light Years

The size of the stars

I have tried to make an image showing the proportions of the stars compared to our sun. I have omitted Taygeta and Sterope since they are double star systems.

Star (Alt. name)	Estimated solar radiuses	Estimated diameter in km
Pleione (28 Tauri)	2.15	2,996,536.30
Celaeno (16 Tauri)	2.58	3,593,732.48
Electra (17 Tauri)	4.68	6,512,842.58
Merope (23 Tauri)	4.71	6,558,119.76
Maia (20 Tauri)	5.12	7,127,190.26
Atlas (27 Tauri)	5.84	8,127,848.48
Alcyone (25 Tauri)	7.66	10,662,861.88

Findings by mapping the Pleiades with the Kepler telescope in 2017

Mapping with the Kepler telescope has brought new insights into the Pleiades. Most of the stars of the Pleiades are variable. This means that their brightness is oscillating. Unfortunately, it was not possible to measure the exact frequency since the bright stars are too bright for the sensitive optics until now. Tim White of Aarhus University and his team found a solution to this problem. They evaluated the neighboring pixels around the stars and not the overexposed pixels in the stars. So they could grasp the relative changes in the brightness of these stars. This new method was called halo-photometry by him and his team.
The measurements have shown that there are considerable differences in the frequency at which the stars oscillate. Alcyone, Electra, and Taygeta swing a little slower and more irregularly than the other stars. Some of these differences can be explained by the different properties of the stars. Four of them are spinning very fast. Also, Atlas, Pleione, and Taygeta are known to belong to multiple star systems.
Maia provided a surprise. Decades ago, it was discovered that Maia oscillates in a period of about 2 hours. At that time, the class of Maia variables was created, since these properties did not fit any known kind of variable stars. However, the new data show that Maia does not actually fit into the class named after her. The measurements showed that Maia is swinging much slower than previously thought because her period lasts about 10 days. The rapid change in brightness must, therefore, have another cause. It is believed that these are caused by manganese absorption on the surface of the star and the resulting large chemical spot. Due to the rotation of this star, its dark spot appears regularly in the field of view of the telescopes and has an effect to the brightness of the star. Due to this particularity Maia definitely does not belong to the "Maia variables" with brightness fluctuations in the hour range, the astronomers plead that the whole class should be renamed in future.

Details of the picture that was captured by me

The picture was taken from my backyard with the following settings and following equipment.

Light frames: 12 x 300" and 21 x 600" @ unity gain
Dark frames: 6 x 300" and 6 x 600"
Flat frames: 100 pcs.
Bias frames: 256 pcs.

Camera: QHYCCD247C
Scope: TSAPO65Q · 420mm · f6.5
Guide camera: QHY5L-II
Guide scope: TSL60D · 240mm · f4.0
Mount: Skywatcher AZ EQ-6
All is controlled by my Astro-PC over Remote-Desktop and wireless LAN.

Software: Sequence Generator Pro, PixInsight, Photoshop CC

References:

Thank you very much for visiting and reading!
I hope that this has been a useful article for you. If you have any questions or suggestions, please don't be afraid to let me know of anything you thought about this post!

Yours,
@astrophoto.kevin

All images, otherwise clearly indicated, in this post are my own work.
You can use it for free if you credit them to @astrophoto.kevin.