1 Introduction

Classical Be stars are non-supergiant B stars which show, or have shown, Balmer line emission. In addition they show an infra-red continuum excess due to free free and bound free emission from a dense circumstellar envelope. Comparison of optical and UV spectra reveals the presence of a second circumstellar wind regime; a lower density, high velocity polar component responsible for the high excitation lines visible in UV spectra. That the denser component was concentrated in the equatorial plane has long been suspected. Recent interferometric data has confirmed this hypothesis (Quirrenbach et al. 1994; Stee et al. 1995).

Despite these direct observations of the circumstellar envelope, the dynamics and physical conditions within it are still largely unconstrained. Determination of parameters such as the density and temperature gradient of the disc would allow constraints to be placed on theoretical models of the Be phenomenon. At present some success has been achieved by modeling the continuum excess and H$\alpha$ line profile (Waters 1986; van Kerkwijk et al. 1995). However, the optical Hydrogen transitions do not allow us to probe the inner regions of the circumstellar disc. The rich recombination spectrum of Be stars in the near-IR provides a powerful tool to address these problems, given that the lines present at these wavelengths are likely to originate at smaller disc radii than those present in the optical region. Therefore, we can use near-IR spectra to probe the inner regions of the circumstellar disc where it is possible that deviations from a quasi-Keplerian disc may occur, due to transport of angular momentum, for example. Additionally, given that near IR wavelengths are less affected by interstellar extinction, it is hoped that a spectral classification scheme for classical Be stars can be developed for use in situations where standard optical classification is inappropriate (such as the identification of highly reddened counterparts to X-ray transient systems where it is impossible to obtain optical spectra for classification purposes).

This paper is the second of a series on the optical and near IR spectral properties of a representative sample of Be stars. In Steele et al. (1999) (Paper I) we presented optical spectra of a sample of 58 Be stars. The sample contains objects from O9 to B8.5 and of luminosity classes III (giants) to V (dwarfs), as well as three shell stars. A spectral type and value of $v \sin i$ was derived for each object in the sample. The sample is termed a "representative'' sample, in that it was selected in an attempt to contain several objects that were typical of each spectral and luminosity class in the above range. It therefore does not reflect the spectral and luminosity class space distribution of Be stars, but only the average properties of each subclass in temperature and luminosity. The distribution of $v \sin i$ within each temperature and luminosity class was carefully investigated and the conclusion drawn that there were no significant selection effects biasing the average properties of the objects.

This paper (Paper II) presents K band (2.05-2.22 $\mu$m) spectra of the 58 stars from Paper I, plus eight additional objects (Tables 1 and 2). The spectra show H I, He I and various metallic transitions. This paper discusses the relationships between the properties of the underlying B stars in the sample (from Paper I) with those of the observed transitions. Future papers in this series will extend this approach to the emission features present in optical, near-infrared and infra-red H band spectra of the same sample, with the eventual intention of modelling the combined datasets.

 

Table 1: Summary of the stellar parameters of the program stars (I). The spectral classifications and values of v sin i are from Paper I. Those values in italics are taken from the literature. w sin i is the projected breakup velocity of the star; see Sect. 5 for a further description. The morphological classification of each spectrum according to the criteria listed in Sect. 3 is listed in Col. 6, and the date of each observation (in 1996) in Col. 7

Object name	Aliases	Spectral Type	$v \sin i$	$\omega \sin i$	Group	Date
CD-28 14778	HD 171757	B2III	153 $\pm$ 21	0.42	1	29/06
CD-27 11872	V3892 Sgr, HD 161103	B0.5V-III	224 $\pm$ 33	0.48	1	29/06
CD-27 13183	HD 172158	B7V	174 $\pm$ 10	0.43	5	29/06
CD-27 16010	$\epsilon$ PsA, HR 8628, HD 214748	B8IV	187 $\pm$ 32	0.54	5	28/06
CD-25 12642	HD 164741	B0.7III	77 $\pm$ 18	0.19	2	29/06
BD-20 05381	HD 177015	B5V	202 $\pm$ 10	0.45	5	28/06
BD-19 05036	V3508 Sgr, HD 170682	B4III	121 $\pm$ 10	0.32	4	29/06
BD-13 00893	DU Eri, HR 1423, HD 28497	B1-3V	270	0.57	1	30/09
BD-12 05132	HD 172252	BN0.2III	120 $\pm$ 43	0.29	1	29/06
BD-08 00929	HD 30076	B2V	-	-	3	30/09
BD-05 01710	HR 2418, HD 47054	B8V	210	0.52	5	02/10
BD-02 05328	HD 196712	B7V	151 $\pm$ 15	0.35	5	28/06
BD-01 03834	HD 187350	B2IV	168 $\pm$ 34	0.41	1	28/06
BD-00 01468	HD 50209	B9V	-	-	5	02/10
BD-00 03543	HD 173371	B7V	271 $\pm$ 54	0.66	5	29/06
BD+00 01203	HD 39447	B5III	-	-	5	01/10
BD+01 01005	$\psi$01 Ori, HR 1789, HD 35439	B1-3V	-	-	1	01/10
BD+02 03815	HD 179343	B7-8sh	224 $\pm$ 14	0.62	5	28/06
BD+04 01002	47 Ori, HR 1934, HD 37490	B2-3III	155	0.33	1	01/10
BD+05 03704	HD 168797	B2.5V	221 $\pm$ 10	0.47	1	29/09
BD+17 04087	HD 350559	B6III-V	156 $\pm$ 39	0.42	4	28/09
BD+19 00578	13 Tau, HR 1126, HD 23016	B8V	240 $\pm$ 70	0.59	4	30/09
BD+20 04449	HD 191531	B0III	81 $\pm$ 11	0.19	2	28/06
BD+21 04695	25 Peg, HD 210129	B6III-V	146 $\pm$ 10	0.40	5	28/06
BD+23 01148	HD 250289	B2III	101 $\pm$ 10	0.28	2	02/10
BD+25 04083	HD 339483	B0.7III-B1II	79 $\pm$ 11	0.20	2	28/06
BD+27 00797	HD 244894	B0.5V	148 $\pm$ 74	0.27	2	01/10
BD+27 00850	HD 246878	B1.5IV	112 $\pm$ 25	0.26	2	02/10
BD+27 03411	$\beta$2 Cyg, HR 7418, HD 183914	B8V	194 $\pm$ 10	0.56	5	28/06
BD+28 03598	HD 333452	O9II	90 $\pm$ 12	0.21	2	28/06
BD+29 03842	HD 33226	B1II	91 $\pm$ 16	0.23	2	28/06
BD+29 04453	HD 205618	B1.5V	317 $\pm$ 20	0.63	1	28/06
BD+30 03227	HR 6971, HD 171406	B4V	218 $\pm$ 21	0.48	4	29/06
BD+31 04018	V2113 Cyg, HD 193009	B1.5V	211 $\pm$ 11	0.42	1	29/06
BD+36 03946	HD 228438	B1V	186 $\pm$ 21	0.36	1	28/06
BD+37 00675	HR 894, HD 18552	B7V	207 $\pm$ 29	0.48	5	30/09
BD+37 03856	HD 228650	B0.5V	104 $\pm$ 17	0.19	2	28/06
BD+40 01213	HD 33604	B2.5IV	128 $\pm$ 20	0.32	1	02/10
BD+42 01376	V434 Aur, HD 37657	B2V	196 $\pm$ 10	0.41	1	02/10
BD+42 04538	HD 216581	B2.5V	282 $\pm$ 10	0.6	3	28/06
BD+43 01048	HD 276738	B6IIIsh	220 $\pm$ 20	0.67	5	30/09
BD+45 00933	HD 27846	B1.5V	148 $\pm$ 16	0.29	2	30/09
BD+45 03879	HD 211835	B1.5V	193 $\pm$ 10	0.38	1	28/06
BD+46 00275	$\phi$ And, HR 335, HD 6811	B5III	113 $\pm$ 21	0.33	5	30/06
BD+47 00183	22 Cas, HR 193, HD 4180	B2.5V	173 $\pm$ 12	0.36	3	30/09
BD+47 00857	$\psi$ Per, HR 1087, HD 22192	B4IV-V	212 $\pm$ 16	0.47	3	30/09
BD+47 00939	48 Per, HR 1273, HD 25940	B2.5V	163 $\pm$ 12	0.35	3	30/09
BD+47 03985	EW Lac, HR 8731, HD 217050	B1-2sh	284 $\pm$ 20	0.67	1	28/06
BD+49 00614	HD 13867	B5III	90 $\pm$ 27	0.27	5	30/09

 

Table 2: Summary of the stellar parameters of the program stars (II). Notation as Table 1

Object name	Aliases	Spectral Type	v sin i	w sin i	Group	Date
BD+50 00825	HR 1160, HD 23552	B7V	187 $\pm$ 10	0.44	5	30/09
BD+50 03430	HD 207232	B8V	230 $\pm$ 15	0.56	5	28/06
BD+51 03091	HR 8259, HD 20551	B7III	106 $\pm$ 10	0.33	5	28/06
BD+53 02599	HD 203356	B8V	191 $\pm$ 23	0.47	5	28/06
BD+55 00552	HD 13669	B4V	292 $\pm$ 17	0.65	1	30/09
BD+55 00605	V361 Per, HD 14605	B1V	126 $\pm$ 35	0.25	1	30/09
BD+55 02411	HD 195554	B8.5V	159 $\pm$ 90	0.39	5	29/06
BD+56 00469	V473 Per, HD 13831	B0-2III	167 $\pm$ 28	0.33	1	30/09
BD+56 00473	V356 Per	B1V-III	238 $\pm$ 19	0.54	1	30/09
BD+56 00478	V358 Per, HD 13890	B1.5V	157 $\pm$ 12	0.31	1	30/09
BD+56 00484	V502 Per	B1V	173 $\pm$ 16	0.33	1	30/09
BD+56 00493	-	B1V-IV	270 $\pm$ 10	0.52	2	30/09
BD+56 00511	-	B1III	99 $\pm$ 14	0.25	1	30/09
BD+56 00573	-	B1.5V	250 $\pm$ 58	0.5	1	30/09
BD+57 00681	HD 237056	B0.5V	147 $\pm$ 49	0.27	1	30/09
BD+58 00554	HD 237060	B7V	229 $\pm$ 10	0.54	5	30/09
BD+58 02320	HD 239758	B2V	243 $\pm$ 20	0.51	1	28/06