Candidate Y dwarfs

I guess most, if not all of you, are fans of cool things.
Then, I bet that not only planets but brown dwarfs and low mass stars
along with anything in between will also attracts you attention.
I made a list of Y dwarf suspects. Although those objects
are classified as very late-T dwarfs, I think there is a possibility
that most if not all of them will shift to the next class after
comparison with bona-fide Y objects awaiting for discovery and after
the proper determination of the Y sequence (at least its hot half)
just as Dave Kirkpatrick and Adam Burgasser did for the L and T spectral
classes respectively.
The actual situation resembles 1995 when what astronomers have
at hands was a handful of late-M dwarfs, and two oddities, GD 165B
(classified at that time as (>=M10V ) and Gliese 229B.
Today GD 165B and GJ 229B are well-known, somewhat ordinary L4 and
T7p dwarfs.
The very first 2MASS and DENIS dwarfs were also classified as ">=M10V"
just as the ULAS and CFBS folks are classified as T9 or later or else
T/Y or possibly Y0 as Delorme et al have suggested.
Here`s the list [I sugget to try to cut+past it to a good text editor
like textpad to see it in a decent format!]:

Candidate Y dwarfs
discovery_name J H MH K par spt_ir Teff Mass Age notes
mag mag mag mag mas K MJ Gyr
Alpha PsA b >22.9 >23.47 129.81 0.47 400 1-3 0.2 = Fomalhaut b
SDWFS J143356.62+351849.2 >22.9 >24.2 >20.1 Y?
UGPS J072227.51-054031.2 16.52 16.90 19.56 17.08 341 40 T10/Y0 450 ± 50 5-30 0.1-10
CFBDSIR J221903.07+002417.92 -
ULAS J133553.45+113005.2 17.90 18.25 18.28 * T9 525 ± 25 5-20 0.1-2
Wolf 940 B 18.16 18.77 18.28 18.85 * 79.8 4.5 T8.5 570 ± 25 20-32 3.5-6 = ULAS J214638.83-001038.7
CFBDSIR J145829+101343 19.66 20.12 20.60 T8.5 575 ± 25
CFBDS J005910.90-011401.3 18.06 18.27 18.63 * T9 575 ± 25 10-50 0.5-10 Delorme et al. (2008) list an alternate spectral type of "Y0"
ULAS J003402.77-005206.7 18.15 18.49 17.99 18.48 * 79.6 3.8 T9 575 ± 25 13-20 1-2
GJ 758 B 19.26 18.27 63.45 0.35 T9 593 ± 44 10-40 0.7-8.7
ULAS J130217.21+130851.2 18.11 18.60 18.28 * T8.5
ULAS J123828.51+095351.3 18.95 19.20 * T8.5 600 ± 25 6-10 0.2-1.0
2MASS J09393548-2448279 15.61 15.96 17.32 16.83 * 187.3 4.6 T8 J? 600 ± 100 20-50 2-10
Ross 458 C 16.69 17.01 16.67 16.90 * 85.54 1.53 T7.5-9 600 5-14 0.1-1 = GJ 494 C, = HIP 63510 C
SDSS J141623.94+134836.3 B 17.26 17.58 18.10 18.93 * 127 27 T7.5 p 650 ± 60 22-46 2-10 possible indications of NH3 absorption in the 1.0-1.3 µm region.= ULAS J141623.94+134836.3
appearance of ammonia in the near-infrared near Teff ~600K,
disappearance of the alkali lines near Teff ~500K,
end of the blueward trend of J - Ks color with type near Teff ~350K
onset of water clouds near Teff ~400-500K (has no appreciable effect on the spectra)
coolest Brown dwarfs Teff ~260K (Objects with masses amongst the smallest that the star formation process creates (~10 MJup) and ages similar to the older stars in the Galaxy (6-10 Gyr) are expected to be as cool as Teff ~260 K.)
2MASS J04151954-0935066 15.70 15.54 16.75 15.43 174.34 2.76 T8.0 750 ± 25 33-58 3-10
HD 3651 B 16.16 16.68 16.45 16.87 90.03 0.72 T7.5 810 ± 30 40-72 3-12 companion to planet-host HD 3651; sep=43.07"+/-0.08" @ 289.97+/-0.11deg in June 2006 (Mugrauer et al. 2006). Stated photometry on MKO system (Luhman et al. 2006). Burgasser (2006) has a near-IR spectral type of T8
GJ 570 D 15.32 15.27 16.42 15.24 169.85 0.82 T7.5 810 ± 10 31-47 2-5 located 258.3+/-0.4" @ 316 deg from Gl 570A on 5/16/1998 (Burgasser et al. 2000a)
* photometry on the MKO system


Of course, one or another of those objects could light enough to
be a free floating high mass planet, or those so-called planemo/planetar
things that forms like stars and BDs but that will never fuse anything nor
even Deuterium.
Bruno

Unfortuantely, pasting from a text editor into the post reply results in the loss of formatting information. Copying and then pasting back into a text editor thus does not preserve the formatting (unless I'm not using a good programme).

For what reason is Fomalhaut b in the list?

Hello,
Fomalhaut b has an estimated temperature of 400K, in the realm of the Y dwarfs.
It is also distant from the A-type primary thus this 400K is an intrinsic temperature.
Yes, I know it is a planet but it seems it is OK for a planet to have a Y type just
as it is OK for a planet to have a T, L or even M type (if it is massive and young
enough for that - material form Adam Burrows and othres suggest that a planet
near the deuterium burning limit if very young could shine at pretty high temperatures).

Then why don't add another planets to the list? simply because they do not have
been imaged yet! There could be planets hotter than Fomalhaut b out there and those
need not to be of the scorched (very-) hot jovian variety.
Also, please notice that I included only obects cooler than 700K in this list - this rules out the planets of
Beta pictoris and HR 8799

How could I post the Y dwarf list? could I upload it?
If not i'll manage to have a better format.

The spectral type would be determined by the spectral lines, instead of being strictly a function of temperature. As the mass goes into the planetary regime, the chemistry of the planets may become too diverse to classify into spectral types as we would do for stars.

The natural question would of course be where the dividing limit is, and the distinction between brown dwarfs and planets is still an issue of debate.

You could post an image of the list or you could work through the processing of writing the appropriate pseudo-html (see here).

Thanks!

It's true, I know that spectral types are not strictly dependent upon temperatures.
One must consider abundances, gravity and other variables (I think).
Now, after considering your comments, I'm not sure anymore if Fomalhaut b pertains to this list!

IIRC Fomalhaut b's spectrum is rather odd, perhaps due to scattering from a circumplanetary disc. Not sure if it has even been assigned a spectral type yet. One problem with planets is that they are also reflecting light from their stars, which is going to change the game.

Question is whether there is a need for spectral type Y, or whether it continues down the T-sequence later than T10.

Candidate Y dwarfs

discovery_name	H	MH	par	spt_ir	Teff	Mass	Age
	mag	mag	mas		K	MJ	Gyr
SDWFS J143356.62+351849.2	>24.2			Y?	450?
UGPS J072227.51-054031.2	16.90	19.56	341 ± 40	T10/Y0	450 ± 50	5-30	0.1-10
CFBDSIR J221903.07+002417.92
ULAS J133553.45+113005.2	18.25			T9	525 ± 25	5-20	0.1-2
Wolf 940 B	18.77	18.28	79.8 ± 4.5	T8.5	570 ± 25	20-32	3.5-6
CFBDSIR J145829+101343	20.12			T8.5	575 ± 25
CFBDS J005910.90-011401.3	18.27			T9	575 ± 25	10-50	0.5-10
ULAS J003402.77-005206.7	18.49	17.99	79.6 ± 3.8	T9	575 ± 25	13-20	1-2
GJ 758 B	19.26	18.27	63.45 ± 0.35	T9	593 ± 44	10-40	0.7-8.7
ULAS J130217.21+130851.2	18.60			T8.5
ULAS J123828.51+095351.3	18.95			T8.5	600 ± 25	6-10	0.2-1.0
2MASS J09393548-2448279	15.96	17.32	187.3 ± 4.6	T8 J?	600 ± 100	20-50	2-10
Ross 458 C	17.01	16.67	85.54 ± 1.53	T7.5-9	600	5-14	0.1-1
SDSS J141623.94+134836.3 B	17.58	18.10	127 ± 27	T7.5 p	650 ± 60	22-46	2-10
2MASS J04151954-0935066	15.54	16.75	174.34 ± 2.76	T8.0	750 ± 25	33-58	3-10

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Notes:
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Criteria of inclusion
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1) If avalilable, Teff <= 600K
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2) Spt_ir > T8 if Teff is not available
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Hipparcos parallaxes are those derived from the new reduction on van Leeuwen (2007)
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CFBDS J005910.90-011401.3 Delorme et al. (2008) list an alternate spectral type of "Y0" Delorme also listed some dwarfs in this list as T/Y in another paper [what dwarfs and what paper?].
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Wolf 940 B = ULAS J214638.83-001038.7
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Ross 458 C = GJ 494 C = HIP 63510 C
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SDSS J141623.94+134836.3 B = ULAS J141623.94+134836.3. It shows possible indications of NH3 absorption in the 1.0-1.3 µm region Notice that its temperature is close to that of the appearance of ammonia in the near-infrared below.
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2MASS J04151954-0935066 is not an Y dwar candidate. It is included here for the sake of comparison only (it is the prototype T8.0 V dwarf). Notice that its temperature is 100K higher than the next hottest object, SDSS J141623.94+134836.3 B Also, its absolute H magnitude, with the exception of Ross 458 C is more than 1 magnitude brighter than the MH of the others (2MASS J09393548-2448279 is a possible binary)
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Some interesting indicators:
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a) appearance of ammonia in the near-infrared: Teff ~600K,
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b) disappearance of the alkali lines: Teff ~500K,
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c) end of the blueward trend of J - Ks color with type: Teff ~350K
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d) onset of water clouds: Teff ~400-500K (has no appreciable effect on the spectra)
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e) coolest Brown dwarfs: Teff ~260K (Objects with masses amongst the smallest that the star formation process creates (~10 MJup) and ages similar to the older stars in the Galaxy (6-10 Gyr).)