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Thread: What is the second well known white dwarf?

  1. #1
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    What is the second well known white dwarf?

    I think Sirius B is the most populair white dwarf ,but i dont know the second well known white dwarf. Somebody who knows that? Thanks.

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    Probably the center of the Ring Nebula in Lyra.
    Forming opinions as we speak

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    I would guess Procyon B is fairly well known.

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    Not your original question, but the second known (i.e. discovered) white dwarf is Van Maanen's Star
    Mira B is well known as well. Mira A will normally become a white dwarf "soon" as well (soon in the lifetime of a star, that is).

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    Why is a white dwarf less bright than the sun ,while a white dwarf is hotter than the sun.

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    Because it's a lot smaller. Much small radiating area more than compensates for it being brighter per unit of radiating area.

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    Quote Originally Posted by Denis12
    Why is a white dwarf less bright than the sun ,while a white dwarf is hotter than the sun.
    The luminosity of a star is proportional to its temperature and its surface area. Even though a white dwarf may be hotter than the Sun, its surface area is on the same order of magnitude as the Earth. White dwarfs are less bright because they are so small.

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    Because it is very much smaller. A white dwarf can be fantastically hot (100,000 degrees K when newly formed) but is very small- most are smaller than the Earth.
    Next to the Sun a white dwarf would be a tiny, but brilliant point. The Sun is five hundred times as bright as Sirius B, for example.
    White dwarfs do not produce energy by fusion, by the way; they shine simply because they are so hot, and it will take a long time to cool down through the small surface area of such an object.

  9. #9
    The existence of both Sirius and Procyon B was inferred a long time ago. However, by far the easiest WD to study from Earth is 40 Eridani B, a star which isn't practically lost in its primary's glare as are the other two. I believe it's also the second brightest WD in the neighborhood, after Sirius B. Van Maanen's star is the brightest stand-alone, but it's considerably fainter.

  10. #10
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    Quote Originally Posted by Denis12
    ... the second well known white dwarf.
    Either Grumpy or Dopey.

  11. 2006-Apr-04, 06:21 PM
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  12. #11
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    Quote Originally Posted by Romanus
    The existence of both Sirius and Procyon B was inferred a long time ago. However, by far the easiest WD to study from Earth is 40 Eridani B, a star which isn't practically lost in its primary's glare as are the other two. I believe it's also the second brightest WD in the neighborhood, after Sirius B. Van Maanen's star is the brightest stand-alone, but it's considerably fainter.
    Why is Van Maanens star considerably fainter? And what are its other names? HD ,SAO or others? Is it pretty to have a white dwarf at the distance and place of our Moon?

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    It is possible to view Sirius B in amateur scopes, in case anybody here wants to try it. The trick is distorting the Airey disk of Sirius to avoid the glare swamping out Sirius B. Cut mask out of black poster board that fits the aperture of your scope, and using a compass, lay out a hexagon just inside that aperture and cut it out with a razor knife. When you observe Sirius, you will see that the Airey disk is concentrated into 6 very bright sharp spikes. Rotate the mask a few degrees at a time until Sirius B pops into view in a dark trough between the spikes.

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    Is it pretty to have a white dwarf at the distance and place of our Moon?
    You mean aside from the fact that at the distance of the Moon, a white dwarf would be four times the angular size of the Sun and would be between 10,000 and 20,000 times as bright?

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    Yes i mean that if a white dwarf like Sirius B is as close to us as the Moon is (335,000) kilometers ,and i asked what or how will that be to have a white dwarf at that distance from us. What happens with the climate then and what about the life on earth then? Do we have less or more heat than we have (now) from the Sun? Will you try to answer these questions for me Kaptain K? Thank you

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    I did answer your question! If Sirius B were at the distance of the Moon, the Earth would probably be vaporized. Mercury only receives about 10 times as much energy from the Sun as Earth does, yet its surface temperature is around 800K.

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    Quote Originally Posted by Kaptain K
    I did answer your question! If Sirius B were at the distance of the Moon, the Earth would probably be vaporized. Mercury only receives about 10 times as much energy from the Sun as Earth does, yet its surface temperature is around 800K.
    In addition, I would think that the gravitational tidal forces on the Earth would be enormous from having a nearly a solar mass object at the Moon's distance. If the Earth was within the Roche Limit of Sirius B, I don't think we'd have time to be vaporize before the Earth was shredded.*

    [*] I haven't done the calculations so I don't know if this is true, but either way it's not a good day for the Earth.

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    White dwarfs are bad news in many ways; they are so hot most of their luminosity is in the hard UV range, and an Earth-like planet would be bathed in hard radiation even if it were in orbit at a distance which allowed reasonable surface temperatures on such a world.

    If these stars are ever colonised their light will need to be filtered or blocked out altogether. (like in this little scheme of mine -heh heh)

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    Quote Originally Posted by Hamlet
    In addition, I would think that the gravitational tidal forces on the Earth would be enormous from having a nearly a solar mass object at the Moon's distance. If the Earth was within the Roche Limit of Sirius B, I don't think we'd have time to be vaporize before the Earth was shredded.*

    [*] I haven't done the calculations so I don't know if this is true, but either way it's not a good day for the Earth.
    I thought about that, but then I remembered that the Roche Limit is a function of radius. The Earth would be outside of the Roche Limit of Sirius B, at the distance of the Moon.

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    Quote Originally Posted by turbo-1
    It is possible to view Sirius B in amateur scopes, in case anybody here wants to try it. The trick is distorting the Airey disk of Sirius to avoid the glare swamping out Sirius B. Cut mask out of black poster board that fits the aperture of your scope, and using a compass, lay out a hexagon just inside that aperture and cut it out with a razor knife. When you observe Sirius, you will see that the Airey disk is concentrated into 6 very bright sharp spikes. Rotate the mask a few degrees at a time until Sirius B pops into view in a dark trough between the spikes.
    Wow, neat trick. Will have to try that next time I get out of this light-polluted city...

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    What are the other names of Van Maanens Star? Is there a HD or SAO or HIP number of it? And why is Van Maanens Star fainter than other white dwarfs like Sirius B and Procyon B? Will somebody answer this questions? Maybe Antoniseb? Thanks.

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    Quote Originally Posted by Denis12
    What are the other names of Van Maanens Star? Is there a HD or SAO or HIP number of it? And why is Van Maanens Star fainter than other white dwarfs like Sirius B and Procyon B? Will somebody answer this questions? Maybe Antoniseb? Thanks.
    Fram gave you a pretty good link to a wikipedia page about Van Maanen's star and from there you can proceed to solstation.com's page. There's a big list of alternative names:
    Gl 35, Hip 3829, G 1-27, G 70-16, LHS 7, LTT 10292, LFT 76, Wolf 28, WD 0046+05, WD 0046+051, and W 5.
    And about it's faintess. From the links you can see that Van Maanen's star is a bit farther away than Sirius B. But that accounts only for a factor of about 2.6 whereas Van Maanen's star is 38 times fainter than Sirius B. Sirius B is also slightly bigger. On solstation.com page they say that Van Maanen's star is relatively cool star which indicates that it has had time to cool down and is quite a bit older than Sirius B. Sirius B's temperature is around 25 000 K and in Gatewood's and Russel's research paper linked from solstation.com page it says that Van Maanen's star's effective temperature is similar to that of the Sun's which is around 6000 K. Star's luminosity is proportional to the fourth power of its temperature and to the square of its radius. This would explain the difference in the luminosities of these stars quite well, don't you think.

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    When the temperature of Van Maanens Star is the same as that of the Sun ,then it is (not) a white but a yellow dwarf isnt it? And does it have maybe planets?

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    Quote Originally Posted by Denis12
    When the temperature of Van Maanens Star is the same as that of the Sun ,then it is (not) a white but a yellow dwarf isnt it? And does it have maybe planets?
    I don't think it's literally the same as the Sun's.
    I calculated that it would need to have a temperature of something over 13 000 K to be in agreement with the luminosity difference with Sirius B. Its emission peak would be in the UV region at around 220 nanometers. So it would not appear as yellow but more like white or something. Saying a color of a star is not as simple as just pointing out its peak radiation output, ask George, our heliochromologist.

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    2 last questions: 1 What if we put earth in orbit around Van Maanens Star at 1 lightyear distance? What kind of temperature do we have then ,and how bright will Earth illuminated then by the star? Like a full moon at night? 2 What if we put Earth at 1 AU distance from Van Maanens Star ,the same distance we are away from the Sun. Will you answer this last questions? Thank you.

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    I (dont) want to ask this ,but can you answer my last questions please because the thread is sinking away out of the sight. Fine thank you very much.

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    Quote Originally Posted by Denis12
    2 last questions: 1 What if we put earth in orbit around Van Maanens Star at 1 lightyear distance? What kind of temperature do we have then ,and how bright will Earth illuminated then by the star? Like a full moon at night? 2 What if we put Earth at 1 AU distance from Van Maanens Star ,the same distance we are away from the Sun. Will you answer this last questions? Thank you.
    Hi Denis,

    How old are you? We've answered questions like this for you many times, but you don't seem to be retaining the answers, or perhaps are not working very hard to draw your own conclusions about these things. Let me point out that no one here is obliged to answer. We are just like you, people interested in astronomy, here because we choose to be here. We will not bother answering questions that don't interest us. Your questions are getting repetitive. Here are your answers:

    1. If the Earth were one light year from VMS it would be extremely cold. Only the little heat radiating from the Earth would provide warmth. Move to a volcano or hot spring.

    2. If the Earth were at one AU from VMS, it would still be very cold (frozen) and dimly lit, but there would be a lot of extra UV for anyone above the ozone layer.
    Forming opinions as we speak

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    Thank you for answering my questions Antoniseb! By times i am a bit too enthousiast with questions ,because i have fun to think about of how far or what if. So am i.

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    Now i forgot to answer (your) question about how old i am ,well i am 31 years young. And how old are you?

  30. #29
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    Quote Originally Posted by Denis12
    Now i forgot to answer (your) question about how old i am ,well i am 31 years young. And how old are you?
    I'll be fifty-one in a few weeks. I was checking to see if we were talking to a well-informed child or a non-technical adult.
    Forming opinions as we speak

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    Quote Originally Posted by AstroSmurf
    Wow, neat trick. Will have to try that next time I get out of this light-polluted city...
    It works, and the results will impress you.

  32. 2006-Apr-10, 02:32 AM
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