1 Introduction

Nearly several dozens of unusual high-luminosity stars in the Milky Way have been discovered so far. These objects exhibit bright emission lines, infrared (IR) excesses, and other features, which suggest the presence of a large amount of circumstellar matter. They are usually identified with massive ( $M \ge 10\; M_{\hbox{$\odot$ }}$) evolved stars, such as B[e] supergiants (e.g., Zickgraf et al. [1986]), Wolf-Rayet stars, or LBVs. The main feature of B[e] supergiants is a pronounced near-IR excess due to radiation of hot ( $T \sim 1000$ K) circumstellar dust, while Wolf-Rayet stars are recognizable due to their bright and broad high-excitation emission lines of species indicative of a late stage of stellar evolution. The main characteristics of LBVs is their large- ($\sim 5$ mag) and intermediate-amplitude (1-2 mag) photometric variability, which is accompanied by significant spectral variations. During these eruptive events, the star's photosphere increases its size, while its spectrum resembles those of supergiants with a decreasing temperature as the star's brightens (see Humphreys & Davidson [1994] for a review). However, such eruption events are rare, and LBVs spend a long time in quiescence (e.g., P Cyg) which makes it difficult to recognise them among other supergiants. Nevertheless, there are some indicators of quiescent LBVs which can be used in addition to their features of high-luminosity objects. For instance, a strong far-IR excess, which can not be explained by free-free emission of the stellar wind, may point to a dust formation episode or an LBV-type outburst in the past (e.g., AG Car and HR Car).

   

Table 1: Optical photometry of AS314

JD	V	U-B	B-V	V-R	V-I
$^{\rm a}$	9.86	0.13	0.92	-	-
2444025$^{\rm b}$	9.81	0.13	0.87	-	-
2444420$^{\rm b}$	9.87	0.11	0.89	-	-
2444426$^{\rm b}$	9.86	0.11	0.91	-	-
2449940.19$^{\rm c}$	9.84	0.07	0.91	0.89	1.47
2449941.18$^{\rm c}$	9.85	-0.05	0.95	0.92	1.58
2449944.17$^{\rm c}$	9.78	0.04	0.86	0.75	1.31
2451039.21$^{\rm c}$	9.89	-0.05	0.91	0.76	1.40
2451043.19$^{\rm c}$	9.97	-0.03	0.92	0.89	1.54

Data sources: $^{\rm a}$ - Hiltner & Iriarte ([1955]), $^{\rm b}$ - Kozok ([1985a]), $^{\rm c}$ - this paper.

Thus, observational monitoring of such objects is crucial in order to detect their possible eruptions and phase of activity, to constrain the evolution of the object and its circumstellar material, and to study their properties in more detail. Additionally, high signal-to-noise and high-resolution spectroscopic observations are needed to derive reliable physical parameters of these objects. The main aim of this paper is to present new observational data we recently obtained for an early-type emission-line star, AS314, which has not been studied in detail so far.

AS314 = LS5107 = V452Sct was discovered during the Mount Wilson spectroscopic search for emission-line stars in the Milky Way (Merrill & Burwell [1950]). Follow-up low-resolution spectroscopy obtained by Hiltner & Iriarte ([1955]) resulted in the spectral type A3: Ia, while Stephenson & Sanduleak ([1971]) listed it as B9 Ia. The UBVobservations by Hiltner & Iriarte ([1955]) and Kozok ([1985a]), quoted in Table 1, revealed that the star is heavily reddened and that the spectral type, which can be derived from the photometry, is $\rm B9 \,\pm\, 1$. On the basis of the MK classification (A3 Ia), Humphreys ([1970]) estimated its distance from the Sun as 9.6 kpc, while Kozok ([1985b]) derived a value of 1.2 kpc from the color-indices analysis. These estimates suggest very different luminosities for the star.

Later Dong & Hu ([1991]) identified the star with an IRAS point source 18365-1353 with fluxes having a maximum at 60 $\mu$m. This identification made AS314 a potentially interesting object as it points to cold dust associated with the star. AS314 was also a HIPPARCOS target, HIP 91477, for which the parallax $3.58\,\pm\, 1.76$ milliarcseconds was measured with a 2$\sigma$ accuracy. This value can be translated into a distance larger than 280 pc (ESA [1997]). A visual brightness variability of 0.2 mag was also detected during the HIPPARCOS mission.

Recently Venn et al. ([1998]) obtained a high-resolution spectrum of AS314 in the H$\alpha$ region. These authors described the spectrum as a "disk-like'' with "very sharp metallic lines'' and concluded that the object is a Be star rather than a supergiant.

Below we discuss the results of our multicolor photometric and high-resolution spectroscopic observations of AS314. The observations are described in Sect. 2, photometric characteristics and detected spectral lines in Sect. 3, the star's fundamental parameters in Sect. 4. General discussion of our results is given in Sect. 5, while our conclusions are presented in Sect. 6.