|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Difference between 'Optical Spectral Type' and 'IR Spectral Type'?
In the list of L and T dwarfs at 'dwarfarchives.org' (
http://ldwarf.ipac.caltech.edu/archi...rf&format=html ) there are two columns named 'spectral_type_opt' and 'spectral_type_ir'. I guess this comes from the type of instrument used in the measurements? Am I correct? To my knowledge, the Spectral Type indicates the surface temperature of stars. If so why would the optical and infrared spectra give two different measurements? Which one is more accurate? Since the visual spectra of L and T dwarfs are very faint, would the 'infrared spectral type' be more accurate? Thanks |
#2
|
|||
|
|||
Difference between 'Optical Spectral Type' and 'IR Spectral Type'?
On Sun, 27 Feb 2011 17:15:26 -0800 (PST), eric948470
wrote: In the list of L and T dwarfs at 'dwarfarchives.org' ( http://ldwarf.ipac.caltech.edu/archi...rf&format=html ) there are two columns named 'spectral_type_opt' and 'spectral_type_ir'. I guess this comes from the type of instrument used in the measurements? Am I correct? To my knowledge, the Spectral Type indicates the surface temperature of stars. If so why would the optical and infrared spectra give two different measurements? Which one is more accurate? Since the visual spectra of L and T dwarfs are very faint, would the 'infrared spectral type' be more accurate? Thanks It isn't a new system of stellar classification. L, T and Y are just additional stellar classes in addition to O, B, A, F, G, K, M, etc. The L, T and Y objects do have most of their radiation in the infrared. Bud |
#3
|
|||
|
|||
Difference between 'Optical Spectral Type' and 'IR Spectral Type'?
On Feb 27, 9:19*pm, wrote:
On Sun, 27 Feb 2011 17:15:26 -0800 (PST), eric948470 wrote: In the list of L and T dwarfs at 'dwarfarchives.org' ( http://ldwarf.ipac.caltech.edu/archi...t.php?table=lt.... ) there are two columns named 'spectral_type_opt' and 'spectral_type_ir'. I guess this comes from the type of instrument used in the measurements? Am I correct? To my knowledge, the Spectral Type indicates the surface temperature of stars. If so why would the optical and infrared spectra give two different measurements? Which one is more accurate? Since the visual spectra of L and T dwarfs are very faint, would the 'infrared spectral type' be more accurate? Thanks It isn't a new system of stellar classification. *L, T and Y are just additional stellar classes in addition to O, B, A, F, G, K, M, etc. The L, T and Y objects do have most of their radiation in the infrared. Bud Sorry about not making my question more clear. What I have trouble understanding is that that the same star can have two different values in "spectral_type_ir" and "spectral_type_opt". For example, the star "GJ 1001B, LHS 102B" (4th from top) has a "spectral_type_opt" of L5 and a "spectral_type_ir" of L4.5. How can it be both at the same time? And which one is more likely to be accurate? |
#4
|
|||
|
|||
Difference between 'Optical Spectral Type' and 'IR Spectral Type'?
eric948470 wrote:
On Feb 27, 9:19 pm, wrote: On Sun, 27 Feb 2011 17:15:26 -0800 (PST), eric948470 wrote: In the list of L and T dwarfs at 'dwarfarchives.org' ( http://ldwarf.ipac.caltech.edu/archi...t.php?table=lt... ) there are two columns named 'spectral_type_opt' and 'spectral_type_ir'. I guess this comes from the type of instrument used in the measurements? Am I correct? To my knowledge, the Spectral Type indicates the surface temperature of stars. If so why would the optical and infrared spectra give two different measurements? Which one is more accurate? Since the visual spectra of L and T dwarfs are very faint, would the 'infrared spectral type' be more accurate? Thanks It isn't a new system of stellar classification. L, T and Y are just additional stellar classes in addition to O, B, A, F, G, K, M, etc. The L, T and Y objects do have most of their radiation in the infrared. Bud Sorry about not making my question more clear. What I have trouble understanding is that that the same star can have two different values in "spectral_type_ir" and "spectral_type_opt". For example, the star "GJ 1001B, LHS 102B" (4th from top) has a "spectral_type_opt" of L5 and a "spectral_type_ir" of L4.5. How can it be both at the same time? And which one is more likely to be accurate? These actually sound pretty similar. A difference of 0.5 subclasses is not remarkable, especially for two different wavelength regions. Probably the IR type is more accurate, as most of the light is emitted there. You need to remember that the spectral classes are "boxes" containing lots of similar stars, with some up against the higher T side (L4) box boundary and others the low side (e.g., box L6). Or there may be specific boxes for L4.5 and L5.5. There would be very little difference between L5 near the boundary and L4.5 near the boundary. There is a similar discrepancy for hot stars observed optically and in the ultraviolet. -- Mike Dworetsky (Remove pants sp*mbl*ck to reply) |
#5
|
|||
|
|||
Difference between 'Optical Spectral Type' and 'IR Spectral Type'?
In article ,
eric948470 writes: To my knowledge, the Spectral Type indicates the surface temperature of stars. Strictly speaking, it indicates the overall appearance of the spectrum, but that appearance is mostly (though not entirely) governed by temperature. If so why would the optical and infrared spectra give two different measurements? I was hoping to look into this a bit but haven't had time. The most likely reason is that the respective classification systems are based on different (but overlapping) groups of stars. The stars probably differ in surface gravity and metallicity, and these may not be adequately taken into account when assigning spectral types. Or it may be something as simple as low signal to noise in some of the spectra used for establishing the classification systems. The L and T types are relatively new, and no doubt the classification systems will improve with time. Which one is more accurate? Since the visual spectra of L and T dwarfs are very faint, would the 'infrared spectral type' be more accurate? That last is probably the way to bet, but I don't think one could say for sure without studying the spectra of the specific star in question and of the respective classification stars. A difference of one or two spectral subtypes is not surprising, given the various uncertainties. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
How to calculate spectral type? | Oh No | Research | 1 | March 2nd 11 09:17 PM |
How to calculate spectral type? | Steve Willner | Research | 1 | January 27th 11 09:59 PM |
How to calculate spectral type? | mollwollfumble | Astronomy Misc | 1 | January 21st 11 02:42 AM |
Spectral class of FM Lyr? | nytecam | Research | 0 | October 19th 06 06:31 PM |
17mm Type 4 or 16mm Type 5? | Gregory | Amateur Astronomy | 3 | June 8th 05 04:14 AM |