M2.5V

Kirkpatrick(in GrayCorbally09) call Gl 250B the primary M2V standard.

GJ 381 should probably be considered the anchor given its
perigree with Kirkpatrick/Henry/Hawley/Reid, but GJ 250B
is also strong.

Radii for M2.5Vs span ~0.30-0.46 Rsun. I adopt the Mann15 Radius
vs. M_Ks trend for [Fe/H]=0.0 (for M_Ks=6.26) to help guide estimation
of the mean HRD position.

KeenanMcNeil76 standard:     Gl 411 (=HD 95735) - M2.5V 
Kirkpatrick91 standards:     GJ 250B   - M2.5V  (primary standard)
	      		     GJ 381    - M2.5V  (primary standard)
	                     GJ 767B   - M2.5V  (secondary standard)
			     GJ 226    - M2.5V  (secondary standard)
Kirkpatrick94 standards:     GJ 767B   - M2.5V
	      		     GJ 226    - M2.5V
Henry02 standards: 	     GJ 226    - M2.5V  (from Kirkpatrick91)
			     GJ 250B   - M2.5V  (from Kirkpatrick91)
			     GJ 381    - M2.5V  (from Kirkpatrick91)
			     GJ 581    - M2.5V  (from Henry94)
			     GJ 623AB  - M2.5VJ (from Henry94)
			     GJ 644ABD - M2.5VJ (from Henry94)
Kirkpatrick(GrayCorbally09): Gl 250B   - M2.5V  (primary standard)

(B-V)  = 1.449+-0.037 ; GJ 250B secondary standard
(B-V)  = 1.514+-0.014 ; GJ 226 tertiary standard
(B-V)  = 1.533        ; Koen10 median d<25pc M2.5V
(B-V)  = 1.573+-0.007 ; GJ 381 primary standard

(G-J)(M2.5V)   = 2.480 ; Bentley18/interp
(G-Ks)(M2.5V)  = 3.331 ; Bentley18/interp
(Ks-W2)(M2.5V) = 0.277 ; Bentley18/interp
(W1-W2)(M2.5V) = 0.124 ; Bentley18/interp

(Ks-W1)(M2.5V) = 0.153 ; Bentley18/interp
(Ks-W1)(M2.5V) = 0.152 ; fit to Winters15 data for V-Ks=4.43
(Ks-W1)(M2.5V) = 0.126 ; Avenhaus12 for V-Ks=4.43
(Ks-W1)(M2.5V) = 0.120 ; Best18
=> adopt (Ks-W1)(M2.5V) = 0.145 [updated 12/29/2019]


(V-I)  = 2.35 ; Hawley96
(V-J)  = 3.69 (+-0.28 stdev) ; Lepine12

(V-Ks) = 4.350 ; sec. stan. GJ 250B 
(V-Ks) = 4.429 ; ter. stan. GJ 226 
(V-Ks) = 4.447 ; pri. stan. GJ 381 
(V-K)  =  4.5  ; Hawley96
=> adopt (V-Ks)(M2.5V) = 4.43* [last updated 11/3/2019]
=> adopt (B-V)(M2.5V)  = 1.522
=> adopt (U-B)(M2.5V)  = 1.175
=> adopt (V-I)(M2.5V)  = 2.306
=> adopt (V-R)(M2.5V)  = 1.041
=> adopt (R-I)(M2.5V)  = 1.265
=> adopt (V-J)(M2.5V)  = 3.597
=> adopt (V-H)(M2.5V)  = 4.186
=> adopt (H-Ks)(M2.5V) = 0.244
=> adopt (J-H)(M2.5V)  = 0.589
=> adopt (I-Ks)(M2.5V) = 2.124
=> adopt (G-V)(M2.5V)  = -0.949 [last updated 6/1/2018]

(Bp-Rp)(M2.5V) =  2.2906 ; Ross_730    
(Bp-Rp)(M2.5V) = 2.3322 ; GJ_250B    sec. stan.
(Bp-Rp)(M2.5V) = 2.3698 ; GJ_226     ter. stan.
(Bp-Rp)(M2.5V) =  2.3843 ; G_202-45    
(Bp-Rp)(M2.5V) = 2.3866 ; GJ_381     pri. stan.
(Bp-Rp)(M2.5V) =  2.3974 ; L_678-39    
(Bp-Rp)(M2.5V) =  2.4061 ; BD+43_2796  
(Bp-Rp)(M2.5V) =  2.4359 ; CD-40_9712  
(Bp-Rp)(M2.5V) =  2.4413 ; Ross_104    
(Bp-Rp)(M2.5V) =  2.4482 ; L_32-9
(Bp-Rp)(M2.5V) = 2.4657 ; GJ674      exemplar 
(Bp-Rp)(M2.5V) =  2.4727 ; L_49-19    
(Bp-Rp)(M2.5V) =  2.5147 ; CD-68_47   
(Bp-Rp)(M2.5V) =  2.5684 ; BD-07_4003  
(Bp-Rp)(M2.5V) =  2.5914 ; BD-17_588A  
=> adopt (Bp-Rp)(M2.5V) = 2.39 [updated 11/18/2020]

(G-Rp)(M2.5V) =  1.0605 ; Ross_730    M2.5V
(G-Rp)(M2.5V) = 1.0734 ; GJ_250B     sec. stan.
(G-Rp)(M2.5V) =  1.0879 ; L_678-39    M2.5V
(G-Rp)(M2.5V) = 1.0885 ; GJ_226      ter. stan.
(G-Rp)(M2.5V) = 1.0978 ; GJ_381      pri. stan. 
(G-Rp)(M2.5V) =  1.1006 ; BD+43_2796  M2.5V
(G-Rp)(M2.5V) = 1.101   ; color trend M0V-M9V 
(G-Rp)(M2.5V) =  1.1014 ; G_202-45    M2.5V
(G-Rp)(M2.5V) =  1.1106 ; Ross_104    M2.5V
(G-Rp)(M2.5V) =  1.1131 ; L_32-9      M2.5V
(G-Rp)(M2.5V) = 1.1150 ; GJ_674      exemplar
(G-Rp)(M2.5V) =  1.1193 ; CD-40_9712  M2.5V
(G-Rp)(M2.5V) =  1.1203 ; L_49-19     M2.5V
(G-Rp)(M2.5V) =  1.1374 ; BD-17_588A  M2.5V
(G-Rp)(M2.5V) =  1.1384 ; CD-68_47    M2.5V
(G-Rp)(M2.5V) =  1.1434 ; BD-07_4003  M2.5V
=> adopt (G-Rp)(M2.5V) = 1.10 [updated 11/18/2020]
=> adopt (Bp-G)(M2.5V) = 1.29 [updated 11/18/2020; Bp-Rp=2.39, G-Rp=1.10]

(Bp-G)(M2.5V) = 1.2588 ; GJ_250B 
(Bp-G)(M2.5V) = 1.2813 ; GJ_226   
(Bp-G)(M2.5V) = 1.2888 ; GJ_381

M_G(M2.5V) =   8.9092  ; BD+47 2112B                   
M_G(M2.5V) =  9.1175  ; HD 285968                      
M_G(M2.5V) =  9.12199 ; CD-68 47                      
M_G(M2.5V) =  9.12334 ; Ross 85                      
M_G(M2.5V) =  9.19368 ; G 236-1                      
M_G(M2.5V) =  9.19466 ; BD+10 1032                    
M_G(M2.5V) =  9.2865  ; CD-18 359                      
M_G(M2.5V) = 9.29684 ; GJ 381 = MCC 568  pri. stan.                     
M_G(M2.5V) =  9.38132  ; HD 50281B                     
M_G(M2.5V) =  9.41056  ; CD-40 9712                    
M_G(M2.5V) = 9.58317  ; GJ 226 = G 222-11 ter. stan.
M_G(M2.5V) = 9.59     ; Mv=10.61, G-V=-1.02
M_G(M2.5V) = 9.63     ; SIMBAD d<20pc trend for V-Ks=4.43
M_G(M2.5V) = 9.757    ; trend d<10pc SIMBAD
M_G(M2.5V) =   9.96867 ; L 127-97                     
M_G(M2.5V) =   10.0041 ; L 678-39                      
M_G(M2.5V) =   10.1857 ; CD-45 1184                   
M_G(M2.5V) =   10.785  ; CD-17 588B

(G-V)(M2.5V) = -1.0273 ; GJ_226 ter. stan.
(G-V)(M2.5V  = -1.023  ; polynomial fit to SIMBAD d<25pc M dwarfs
(G-V)(M2.5V) = -1.0209 ; GJ_381 pri. stan. 
(G-V)(M2.5V) = -0.9842 ; GJ_250B sec. stan. 
=> adopt (G-V)(M2.5V)  = -1.02 [updated 11/1/2020]
=> adopt (G-Ks)(M2.5V) =  3.41 [updated 12/10/2020] (V-Ks=4.43, G-V=-1.02)

(g-r)(M2.5V) = 1.47 ; Covey07

(r-i)(M2.5V) = 1.102 (+-0.05 rms) ; West05 fit for (V-Ic)=2.306

(z-J)(M2.5V) = 1.423 (+-0.028 rms) ; poly fit to d<100pc GCNS for G-Ks=3.41


Mv(M2.5V) =   10.80 ; Kirkpatrick94
Mv(M2.5V) =  10.74 ; JohnsonApps09 fit for V-Ks=4.43
Mv(M2.5V) =  10.70 ; Finch14 calibration for V-Ks=4.43
Mv(M2.5V) = 10.69 ; EEM fit to Winters+2015 data for V-K=4.43
Mv(M2.5V) = 10.61  ; M_Ks=6.18, V-Ks=4.43  
Mv(M2.5V) = 10.61 ; EEM polynomial fit to MS for V-Ks=4.43
Mv(M2.5V) = 10.61 ; ter. stan. GJ 226
Mv(M2.5V) =  10.44 ; EEM polynomial fit to Reid CNS3 data for V-Ks=4.43
Mv(M2.5V) =  10.38 ; Koen10 median d<25pc M2.5V
Mv(M2.5V) = 10.37 ; sec. stan. GJ 250B
Mv(M2.5V) = 10.33 ; pri. stan. GJ 381
=> adopt Mv(M2.5V)   = 10.61 mag [updated 12/10/2020] (M_Ks=6.18, V-Ks=4.43)
=> adopt M_G(M2.5V)  =  9.59 mag [updated 12/10/2020] (Mv=10.61, G-V=-1.02)
=> adopt M_Ks(M2.5V) =  6.18 mag [updated 12/10/2020] (Mv=10.61, V-Ks=4.43)

M_Ks(M2.5V) =  6.57 ; exemplar GJ 674 = LHS 449
M_Ks(M2.5V) =  6.31 ; JohnsonApps09 fit for V-Ks=4.43
M_Ks(M2.5V) =  6.27 ; Finch14 calibration for V-Ks=4.43
M_Ks(M2.5V) =  6.26 ; EEM fit to Winters+2015 data for V-Ks=4.43
M_Ks(M2.5V) = 6.18 ; EEM polynomial fit to MS for V-Ks=4.43
M_Ks(M2.5V) =  6.18 ; ter. stan. GJ 226  
M_Ks(M2.5V) =  6.02 ; sec. stan. GJ 250B
M_Ks(M2.5V) =  6.01 ; EEM polynomial fit to Reid CNS3 data for V-Ks=4.43
M_Ks(M2.5V) =  5.88 ; pri. stan. GJ 381


Teff(M2.5V) =  3617 +- 19 K ; Pecaut13 (GJ 887)
Teff(M2.5V) = 3534 K ; smooth Teff(SpT) trend
Teff(M2.5V) = 3520 K ; GJ 226 tertiary standard
Teff(M2.5V) = 3510 K ; Passegger18 median Teff for CARMENES M2.5V(N=35)
Teff(M2.5V) =  3500 +- 61 K ; Lepine12
Teff(M2.5V) = 3500 K ; GJ 250B secondary standard
Teff(M2.5V) = 3500 K ; GJ 381 primary standard
Teff(M2.5V) = 3500 K ; empirical L-R relation, for logL=-1.668
Teff(M2.5V) =   3498 +- 56 K  ; non-standard GJ 581 (vonBraun11)
Teff(M2.5V) = 3495 K ; Rajpurohit18(mean for N=22 M2.5Vs)
Teff(M2.5V) = 3475 K ; halfway between M2V (3550K) and M3V (3400K)
Teff(M2.5V) = 3470 K ; Rad=0.4062Rsun for Mann15 calib for M_Ks=6.27, [Fe/H]=0.0
Teff(M2.5V) = 3450 K ; exemplar GJ 674 = LHS 449 
Teff(M2.5V) =   3442 +- 54 K ; non-standard GJ 581 (Boyajian12b) 
Teff(M2.5V) =  3400 K ; Rajpurohit13 (N=3)
Teff(M2.5V) = 3362 K ; Morrell19 <Teff> for stars w/i +-0.05 mag of M_Ks=6.27
Teff(M2.5V) =   3304 +- 13 K ; non-standard GJ 581 (Pecaut13)
Teff(M2.5V) =   3243 +- 14 K ; Pecaut13 (GJ 581)
=> adopt Teff(M2.5V) = 3470 K (logT = 3.540) [updated 4/9/2020]

BCv(M2.5V) = -2.012+-0.013 mag ; GJ 581 (Pecaut13)
BCv(M2.5V) = -1.78 ; BC_Ks=2.65, V-Ks=4.43
=> adopt BCv(M2.5V) = -1.78 [updated 11/3/2019; BC_Ks=2.65, V-Ks=4.43]

BC_Ks(M2.5V) = 2.641 ; Morrell19 trend for G-Ks=3.41
BC_Ks(M2.5V) = 2.652 ; Mann15 for V-J=3.597
BC_K(M2.5V)  = 2.723 ; GJ 581 (Pecaut13) [mbol=8.560+-0.010, Ks=5.837+-0.023]
=> adopt BC_K(M2.5V) = 2.65 [updated 11/3/2019]

logL(M2.5V) =  -1.670 dex ; Morrell19 trend for logL for M_Ks=6.27
logL(M2.5V) = -1.636 dex ; M_Ks=6.18, BC_Ks=2.65, Mbol=8.830
=> adopt logL(M2.5V) = -1.636 [updated 12/28/2020]
=> adopt Mbol(M2.5V) =  8.830 [updated 12/28/2020]

Mass(M2.5V) = 0.3995 Msun ; M_Ks=6.26 => Mann18 calib.
Mass(M2.5V) = 0.403 Msun  ; M_Ks=6.26 => Delfosse00 calib. 
Mass(M2.5V) = 0.432 Msun  ; pri. of GJ54AB, unresolved SpT=M2.5V (Benedict16)
Mass(M2.5V) = 0.445 Msun  ; Benedict16 calibration for M_Ks=6.26
=> adopt Mass(M2.5V) = 0.40 Msun [updated 11/3/2019]

Rad(M2.5V) =  0.460+-0.017   Rsun ; sec. stan. GJ 250B (Yee17)
Rad(M2.5V) =  0.420          Rsun ; Rabus19 trend for Teff=3500K
Rad(M2.5V) = 0.4207         Rsun ; logL=-1.636, Teff=3470K
Rad(M2.5V) =  0.4175         Rsun ; Mann15 trend M_Ks=6.18, [Fe/H]=0.0
Rad(M2.5V) =  0.360+-0.018   Rsun ; exemplar GJ 674 = LHS 449 
Rad(M2.5V) =  0.299+-0.010   Rsun ; Boyajian12b (N=1)*** (see below)
Rad(M2.5V) =  0.299+-0.010   Rsun ; non-standard GJ 581 (vonBraun11)
=> adopt Rad(M2.5V) = 0.421 Rsun [updated 12/28/2020]

*** note that <Radius> for their M3V stars with N=3 is 0.4097+-0.0075 Rsun 

# No Standard
Boeshaar85 does not list an M2.5V standard. 

# Primary Standard

GJ 381 = LHS 2230 = DO 2902 = L 968-22
 *M2.5V: Walker83,Kirkpatrick91(pri),Hawley97,Henry02,Reid04,Kirkpatrick(GrayCorbally09)(pri),Alonso-Floriano15
  M2: Gaidos14
  M3V: Boeshaar76
  M0: Lee47
  
  V=10.64(HIP,TYC1), V=10.640+-0.010(Mermilliod91), V=10.638(Hauck90),
  V=10.629(Koen10), B-V=1.566+-0.012(HIP),
  B-V=1.573+-0.007(Mermilliod91), B-V=1.576(Koen10),
  V-Rc=1.048(Koen10), U-B=1.201+-0.04(Mermilliod91),
  V-I=2.32+-0.01(HIP), V-I=2.326(Koen10), J=7.021+-0.023(2MASS),
  H=6.471+-0.049(2MASS), Ks=6.193+-0.026(2MASS).
  V-Ks=10.640-6.193=4.447(HIP,2MASS).  Teff = 3460K(Morales08),
  3538+-80K(Gaidos14) => <Teff> = 3500K.
  GaiaDR2: plx= 86.6489+-0.7014mas, 
  G=9.6081 0.0008, Bp-Rp=2.3866, Bp-G=1.2888, G-Rp=1.0978.
  Mv = 10.33+-0.02, M_Ks=5.88+-0.02, M_G=9.30. 

# Secondary Standard

GJ 250B = HD 50281B = LHS 1876 = WDS J06523-0510Ba,Bb = 2MASS J06521804-0511241
 *M2.5V: Boeshaar76,Kirkpatrick91(pri),Henry02,Bonfils13
  M2.3V: Mann15
  M2V: Wooley70,KeenanMcNeil76(stan),Luyten79,Bidelman85,Gliese91,Hawley97,Gaidos14,Newton14(near-IR)
  
  Skiff07 shows no published SpTs before Kirkpatrick91 (V=10.1), but
  it was the KeenanMcNeil76 M2V standard! It appears that Kirkpatrick
  & Henry went with the Boeshaar classification over Keenan &
  McNeil's, so it has been an M2.5V standard ever since.  Would prefer
  to see better agreement among modern types (all getting ~M2), but
  I've retained it as a secondary standard since Kirkpatrick
  considered it primary (but it clearly has a worse pedigree than GJ
  381).  V=10.073+-0.029(Mermilliod91), V=10.03(TYC1),
  Vt=10.164+-0.05(TYC1), B-V=1.449+-0.037(Mermilliod91),
  U-B=1.22(Mermilliod91), J=6.579+-0.034(2MASS),
  H=5.976+-0.055(2MASS), Ks=5.723+-0.036(2MASS),
  V-Ks=4.35(Mermilliod91,2MASS), plx=106.69+-1.31mas(vanLeeuwen07),
  plx=114.4148+-0.0516mas(GaiaDR2).
  Teff=3359K(Houdebine10,Houdebine12), 3379K(Terrien15),
  3481+-60K(Mann15#1), 3520K(Morales08),
  3569+-19K(Rojas-Ayala12,Mann15#2), 3892+-76K(Gaidos14) => <Teff> =
  3500K.  R=0.460+-0.017Rsun(Mann15), R=0.436+-0.006Rsun(Mann15#2),
  M=0.444+-0.044(Mann15), M=0.466+-0.008Msun(Mann15#2),
  [Fe/H]=0.14+-0.03(Mann15). Rad=0.460+-0.017Rsun(Yee17).
  Mv=10.37+-0.03, M_Ks=6.02+-0.04. 

# Tertiary Standard

GJ 226 = G 222-11 = 2MASS J06101978+8206256
  M2V: Lee47(M2),Hawley97,Reiners12,Neves13,Shkolnik14
 *M2.5V: Bidelman85,Kirkpatrick91(sec),Kirkpatrick94,Henry02,Dieterich12,Lepine13
  M3V: Stephenson86,Gaidos14

 I've put it as tertiary standard as Kirkpatrick considered in a
  secondary standard, but multiple studies have put it as either M2 or
  M3 since. However its color (V-Ks=4.43), absolute magnitudes
  (Mv=10.61, M_Ks=6.18, M_G=9.59) place it closer to the middle of the
  pack among other M2.5Vs, and it appears to be just slightly
  metal-poor ([Fe/H] ~ -0.1). Teff=3583+-68K(Gaidos14),
  3520K(Lepine13), 3470K(Morales08).  R=0.43+-0.04Rsun(Gaidos14),
  L=0.027+-0.06Lsun(Gaidos14).  V=10.490+-0.010(Mermilliod91),
  V=10.488(Hauck90), V=10.48(HIP), V=10.42(TYC),
  B-V=1.524+-0.010(Mermilliod91), B-V=1.514+-0.014(HIP),
  U-B=1.180+-0.013(Mermilliod91), J=6.869+-0.023(2MASS),
  H=6.295+-0.017(2MASS), Ks=6.061+-0.018(2MASS),
  V-Ks=4.429+-0.021(Mermilliod91,2MASS). Gaia EDR3: plx=
  105.6903+-0.0142mas, G=9.47.  Mv=10.61+-0.01, M_Ks=6.18+-0.02,
  M_G=9.59. [Fe/H]: -0.14(Neves13#2), -0.11+-0.16(Schweitzer19),
  -0.07(calc using SchlaufmanLaughlin10), 0.00(Neves13#1), 0.02(calc
  using JohnsonApps09). JohnsonApps09 calibration suggests it is +0.13
  mag (below MS).

# Exemplar

GJ 674 = LHS 449 = HIP 85523 = LTT 6942 = CD-46 11540 = 2MASS J17283991-4653424
  K5: 1939cfsc.book.....S 
  M2V(e): Riaz06
  M2+V: Gray06
 *M2.5: Reid95/Hawley97
  M3V: Walker83,Bidelman85(M3),Torres06,Gaidos14(M3)
  M4: Luyten79

  Include here as it is a well-characterized exoplanet host with
  interferometrically measured diameter, and whose modern types
  bracket M2V-M3V, and with PMSU type M2.5V. Exoplanet (Bonfils07
  2007A&A...474..293B) is 11 Me in 4.7 day orbit.  Vereshchagin15
  includes in Castor stream.  plx = 219.8012+-0.0487mas(GaiaDR2).
  Koen10: V=9.407, B-V=1.566, U-B=1.204, V-Rc=1.070, V-Ic=2.401.
  Ks=4.855+-0.018(2MASS).  V-Ks = 9.407 - 4.855 = 4.552.  Mv=11.12,
  M_Ks=6.57+-0.02.  Teffs: 3409+-25K(Rabus19), 3451+-157K(Stassun19),
  3453+-75K(Gaidos14), 3456+-92K(Hojjatpanah19), 3460K(Morales08),
  3478+-100K(Houdebine16), 3570K(Wright11) => <Teff> ~ 3450K.
  Rad=0.35+-0.05Rsun(Gaidos14),
  Mass=0.36+-0.07Msun(Gaidos14). Rabus19: tetLD=0.737+-0.037mas, fbol
  = (2.443+-0.232)e-8 erg/s/cm2 (mbol = 7.533+-0.103 IAU2015 scale),
  Rad = 0.360+-0.018 Rsun, Teff= 3409+-25K.
  G=8.3306 0.0012, Bp-Rp=2.4657, Bp-G=1.3507, G-Rp=1.1150.

# Deprecated Standards

GJ 767B = BD+31 3767B = HD 331161B
  M2.5V: Kirkpatrick91(sec),Kirkpatrick94
  M1V: Cowley82
  
  Star is 5" binary and some SpTs are A+B (M2; Neckel58; M0; Lee47)

GJ 411 = HD 95735 = Lalande 21185 = LHS 37 (J1103+3558)
 *M2V: JM53,Abt68,Houk,Boeshaar76,Kirkpatrick91(pri),Kirkpatrick93,Henry94,Hawley97,Reid04
  M2+V:  Keenan88,Keenan89,Keenan99
  M2.5V: KeenanMcNeil76(stan)

  Saturated in 2MASS (mags of ~0.3 mag precision quoted). [Fe/H] =
  -0.2 (Zboril98). V=7.49(HIP), B-V=1.502+-0.014(HIP),
  U-B=1.124+-0.015(Mermilliod91), V-I=2.07+-0.02(HIP),
  V-I=2.16(Platais03), R-I=1.14(Delfosse98), J=4.09+-0.10(Reid04),
  Ks=3.35+-0.10(Reid04), K=3.36(Leinert97). V-J=3.40+-0.10(HIP &
  Reid04) (V-Ks)=4.13(HIP & Leinert97). Segrensan03 VLTI study reports
  M = 0.403+-0.02 Msun, R = 0.393+-0.008 Rsun, logg = 4.85+-0.03 dex,
  Teff=3570+-42 K.

GJ 581 = Wolf 562 = BD-7 4003
  M2V:   Newton14(near-IR)
  M2.5V: Henry94,Henry02
 *M3V:   Bidelman85(M3),Stephenson86,Hawley97,Reiners12,Dieterich12,Lurie14
  M3.2:  Mann15
  M3.5V: Walker83
  M4V: Joy74

  Exoplanet host star. Teff=3395+-60K(Mann15),
  [Fe/H]=-0.15+-0.08(Mann15), -0.07+-0.12(Newton14).  Henry group
  changed type from M2.5V (Henry94,Henry02) to M3V
  (Dieterich12,Lurie14), and since others have classified it anywhere
  between M2 to M3.2, I've dropped it as an M2.5V standard but adopted
  it as a M3V exemplar. Mermilliod91: V=10.572+-0.009,
  B-V=1.601+-0.009, U-B=1.205+-0.013. Kmag=5.837+-0.023(2MASS).
  Rabus19 reports: tetLD=0.476+-0.007mas, fbol=(0.967+-0.039)e-8
  erg/s/cm2 (=> mbol = 8.539+-0.044 IAU2015 scale),
  Rad=0.322+-0.005Rsun, Teff=3366+-28K, BCv = mbol - V = 8.539 -
  10.572 = -2.033. BC_Ks = mbol - Ks = 8.539 - 5.837 = 2.702.
  
# Other stars

GJ 408 = LHS 6193 = HIP 53767 = LTT 12942 = StKM 2-688
  M2V: Vyssotsky46,Royas-Ayala12(M2)
 *M2.5V: Henry94,Lurie13
  M3: Bidelman85,Gaidos14
  M4V: Stephenson86