# First high-resolution optical spectra of the distant emission-line star VES 723 (IRAS 02110+6212)

A. S. Miroshnichenko, V. G. Klochkova, E. L. Chentsov, V. E. Panchuk, M.

V. Yushkin, N. Manset

► To cite this version:

A. S. Miroshnichenko, V. G. Klochkova, E. L. Chentsov, V. E. Panchuk, M. V. Yushkin, et al. First high-resolution optical spectra of the distant emission-line star VES 723 (IRAS 02110+6212). Monthly Notices of the Royal Astronomical Society, 2021, 507, pp.879-885. 10.1093/mnras/stab2193. insu-04863681

HAL Id: insu-04863681

https://insu.hal.science/insu-04863681v1

Submitted on 4 Jan 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

# First high-resolution optical spectra of the distant emission-line star VES 723 (IRAS 02110+6212)

A. S. Miroshnichenko<sup>1,2,3*</sup> V. G. Klochkova,<sup>4</sup> E. L. Chentsov,<sup>4</sup> V. E. Panchuk,<sup>4*</sup> M. V. Yushkin<sup>4</sup>
and N. Manset<sup>5</sup>

<sup>1</sup>Department of Physics and Astronomy, University of North Carolina at Greensboro, PO Box 26170, Greensboro, NC 27402–6170, USA

<sup>2</sup>Main Astronomical Observatory of the Russian Academy of Sciences, Saint-Petersburg, Russia

<sup>3</sup>Fesenkov Astrophysical Institute, Observatory 23, 050023, Almaty, Kazakhstan

<sup>4</sup>Special Astrophysical Observatory of the Russian Academy of Sciences, Nizhnyj Arkhyz, Russia

<sup>5</sup>CFHT Corporation, 65–1238 Mamalahoa Hwy, Kamuela, HI 96743, USA

Accepted 2021 July 26. Received 2021 July 26; in original form 2021 June 12

## ABSTRACT

The first high-resolution spectra (resolving powers of $R \ge 60\,000$) of the emission-line star VES 723, which has an unknown evolutionary status, were taken at the 6-m Big Telescope Alt-Azimuthal and the 3.6-m Canada-France-Hawaii Telescope. The spectrum is dominated with powerful emission lines of neutral hydrogen and helium, and forbidden singly ionized nitrogen. The Hα and He I lines were found to exhibit broad foundations of the emission profiles at least $250 \text{ km s}^{-1}$ wide. The strongest emission lines exhibit no noticeable variations during the observing period (2011–2017) except for the He I lines. The spectra contain multicomponent interstellar absorptions of Na I and K I (mult. 1) and several strongest diffuse interstellar bands, while photospheric absorptions have not been detected. The average radial velocity of the forbidden [N II] emission line centres was adopted as the systemic velocity ($V_{\text{sys}} \approx -52 \text{ km s}^{-1}$), which indicates a large distance of $\approx 6 \text{ kpc}$. Our luminosity estimates of log $L/L_{\odot} = 3.7–4.0$ for two different Gaia distance measurements, along with an effective temperature of $T_{\text{eff}} = 25\,000 \pm 2000 \text{ K}$ and a fast decrease of the infrared flux longward of $\lambda \sim 10 \text{ µm}$, allow us to suggest that VES 723 is neither a pre-main-sequence Herbig B[e] star nor a B[e] supergiant but rather a member of the FS CMa group of objects with the B[e] phenomenon.

**Key words:** stars: emission-line, Be–stars: individual: VES 723 (IRAS 02110+6212).

## 1 INTRODUCTION

VES 723 was discovered in the course of the Vatican survey for emission-line stars (Coyne & MacConnell 1983) and mentioned as an object with the B[e] phenomenon by Miroshnichenko et al. (2011). The star is the optical counterpart of the infrared source IRAS 02110+6212. Our long-term experience in studies of various emission-line stars (see our previous papers, such as Klochkova & Chentsov 2004, 2016; Miroshnichenko 2007; Chentsov, Klochkova & Miroshnichenko 2010; Klochkova et al. 2016; Miroshnichenko et al. 2020) led us to notice this poorly studied object. VES 723 is faint in the optical spectral region with an average brightness of $V \sim 13.3$ mag in the All-Sky Automated Survey for Supernovae (ASAS-SN) data base (Kochanek et al. 2017), and it is fainter at shorter wavelengths ($B = 14.0$ mag; Zacharias et al. 2013), which explains the absence of published spectral properties and evolutionary status. This has motivated us to observe VES 723 at a high spectral resolution in the optical region.

## 2 OBSERVATIONS, DATA REDUCTION AND ANALYSIS OF THE SPECTRA

Spectra of VES 723 were obtained at two telescopes: the 6-m Big Telescope Alt-Azimuthal (BTA) with the echelle spectrograph NES ($R = 60\,000$; Panchuk, Klochkova & Yushkin 2017) stationary, located in the Nasmuth focus, and the 3.6-m Canada-France-Hawaii Telescope (CFHT) with the spectropolarimeter ESPaDOnS ($R \ge 65\,000$; Manset & Donati 2003).

The spectrograph NES is equipped with a large-format CCD detector, which has $4608 \times 2048$ pixels with a pixel size of $0.0135 \times 0.0135 \text{ mm}^2$ and a readout noise of 1.8 electrons. The spectral range registered in the NES data was $\lambda\lambda 5300–6700 \text{ Å}$ in 2011 January and $\lambda\lambda 5400–8400 \text{ Å}$ in 2014 October.

Spectral order extraction was performed with the ECHELLE context in the MIDAS package. Traces of cosmic rays were removed by median averaging of two consecutively taken spectra. Wavelength calibration was performed using spectra of a hollow cathode ThAr lamp. All the remaining steps of the data reduction, including photometric and positional measurements, were performed using the latest version of the DECH20t software package.<fnref n="1" />

<footnote>* E-mail: a.mirosh@uncg.edu (ASM); valenta@sao.ru (VEP)</footnote>

<footnote n="1">¹http://www.gazinur.com/DECH-software.html</footnote>
<table><caption>**Table 1.** Heliocentric $V_r$ in the spectra of VES 723.</caption><thead><tr><th rowspan="3">Line ID</th><th colspan="4">2011/01/12</th><th colspan="4">2014/10/04</th><th colspan="4">2017/08/12–14</th></tr><tr><th rowspan="2">r</th><th colspan="3">V<sub>r</sub> (km s<sup>-1</sup>)</th><th rowspan="2">r</th><th colspan="3">V<sub>r</sub> (km s<sup>-1</sup>)</th><th rowspan="2">r</th><th colspan="3">V<sub>r</sub> (km s<sup>-1</sup>)</th></tr><tr><th>top</th><th>blue</th><th>red</th><th>top</th><th>blue</th><th>red</th><th>top</th><th>blue</th><th>red</th></tr></thead><tbody><tr><td>H α 6562.82</td><td>4.62</td><td>-53</td><td>-90</td><td>-20</td><td>4.18</td><td>-55</td><td>-90</td><td>-25</td><td>4.20</td><td>-55</td><td>-94</td><td>-16</td></tr><tr><td>He I(11) 5875.72</td><td>3.35</td><td>-61</td><td>-100</td><td>-20</td><td></td><td></td><td></td><td></td><td>3.17</td><td>-101</td><td>-118</td><td>-71</td></tr><tr><td>He I(46) 6678.15</td><td>3.02</td><td>-58</td><td>-100</td><td>-25</td><td>2.60</td><td>+17</td><td></td><td></td><td>3.10</td><td>-84</td><td></td><td></td></tr><tr><td>He I(10) 7065.32</td><td></td><td></td><td></td><td></td><td>3.80</td><td>-5</td><td></td><td></td><td>4.67</td><td>-91</td><td></td><td></td></tr><tr><td>He I(45) 7281.35</td><td></td><td></td><td></td><td></td><td>2.20</td><td>-17:</td><td></td><td></td><td>2.36</td><td>-77</td><td></td><td></td></tr><tr><td>[N II](3F) 5754.64</td><td>1.66</td><td>-52</td><td>-100</td><td>0:</td><td>1.67</td><td>-48</td><td>-90</td><td></td><td>1.51</td><td>-60</td><td>-113</td><td>-19</td></tr><tr><td>[N II](1F) 6548.03</td><td>1.52</td><td>-52</td><td>-90</td><td>-8</td><td>1.49</td><td>-50</td><td>-85</td><td>-15</td><td>1.47</td><td>-54</td><td>-71</td><td>-40</td></tr><tr><td>[N II](1F) 6583.45</td><td>2.70</td><td>-52</td><td>-90</td><td>-20</td><td>2.42</td><td>-51</td><td>-90</td><td>-20</td><td>2.34</td><td>-59</td><td>-77:</td><td>-40:</td></tr></tbody></table>

Notes. The line rest wavelength is shown in column 1. The line relative intensity in the continuum units is denoted by *r*. The radial velocities $V_r$ are shown at the maximum intensity of each line (top) and at the line connection with the local continuum (blue and red edges). Uncertain measurements are marked with a colon.

Systematic errors of the heliocentric $V_r$, estimated from the sharp interstellar components of the Na I lines, do not exceed 0.25 km s⁻¹ (for each line). The $V_r$ uncertainties of other lines shown in Table 1 are ~0.5 km s⁻¹. Identification of the features in the spectrum of VES 723 was performed based on our earlier paper (Klochkova & Chentsov 2016) devoted to spectroscopy of a similar emission-line star MWC 17, data for which were obtained with the same equipment at the 6-m telescope.

The CFHT spectra were obtained during two observing runs (2017 August 12–14 and 2017 September 10–11) in the range of 3600–10 500 Å and reduced with the UPENA and LIBRE-ESPRIT software packages (Donati et al. 1997). Six 1800-s exposures were taken and combined into one spectrum in each run. A typical signal-to-noise ratio (S/N) in the continuum of both BTA and CFHT spectra was S/N ~ 50. It is changing from 50 to 70 along an echelle spectral order, while it reaches ~100 across the emission lines.

# 3 RESULTS

## 3.1 Features of the optical spectrum of VES 723 and radial velocities

We confidently identified emission lines of neutral hydrogen (H α, H β and Paschen series), helium (e.g. 4471, 4713, 4921, 5018, 5876, 6678, 7065 and 7281 Å), singly ionized iron (e.g. 5169 and 5316 Å), nitrogen, silicon (e.g. 6347 and 6371 Å) and oxygen (e.g. 8446 Å) as well as forbidden emission lines of [O I] and [N II] (5755, 6548 and 6583 Å). The absorption-line spectrum is represented by interstellar features of Na I (mult. 1) and K I 7699 Å, and the strongest diffuse interstellar bands (DIBs).

The strong H α line, which consists of a broad pedestal and a narrow top, is shown in Fig. 1. A complicated profile of the He I 5876 Å line is shown in the left panel of Fig. 2. The profiles of other He I lines are similar to one another. A comparison of the He I 5876 and 6678 Å line profiles in the 2011 spectrum is shown in the right panel of Fig. 2. Both profiles from 2017 shown in Fig. 2 are double-peaked. Such a line profile shape typically forms in a disc-like circumstellar envelope. We also detected intensity variations of the long-wavelength component, while the absorption minimum remained at the same position. Obviously spectral monitoring is needed to understand the temporal profile variations.

The forbidden emission line of [N II] (mult. 1F) 6583.45 Å is shown in Fig. 3. Permitted and forbidden lines of several other elements are shown in Fig. 4. Table 1 presents parameters of selected

<figure><img src="image_3.png" /><figcaption>**Figure 1.** H α profiles in the spectra of VES 723 taken at different times: 2011 January (blue line), 2017 August (black line) and 2017 September (red line). The short vertical line shows the position of the forbidden [N II] 6548 Å line. The vertical dashed line shows the adopted systemic velocity $V_{sys} = -52$ km s⁻¹. Intensity is normalized to the local continuum, and the wavelength scale is heliocentric.</figcaption></figure>

lines. In particular, it lists residual intensities of the line tops (*r*) and heliocentric $V_r$ for the narrow emission components of the entire profiles as well as $V_r$ for the short- and long-wavelength profile edges.

The above-described lines of hydrogen, helium and forbidden nitrogen have a central narrow component above a broad and probably double-peaked pedestal. The latter reaches at least a $V_r$ of ±250 km s⁻¹ from the H α and H β line centres. The narrow component is clearly seen in the forbidden lines of nitrogen ([N II](1F)). Its slopes are nearly vertical and located at ±35 km s⁻¹ from the line centre. The $V_r$ of the line centres coincide within the measurement errors. Therefore, the average $V_r$ can be adopted as the systemic velocity of VES 723, $V_{sys} = -52$ km s⁻¹.
<figure><img src="image_4.png" /><figcaption>**Figure 2.** Left panel: the He I 5876 Å line profiles in the spectra of VES 723 taken at different times. The line colours indicate the spectra taken at the same dates as in Fig. 1. Right panel: the He I 5876 and 6678 Å line profiles in the spectrum taken in 2011. The vertical dashed line in both panels shows the adopted systemic velocity $V_{\text{sys}} = -52 \text{ km s}^{-1}$. The intensity and wavelength scales are in the same units as in Fig. 1.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Figure 3.** The [N II] 6583 Å line profiles in the spectra of VES 723 taken at different times. The line colours and the vertical dashed line have the same meaning as in Fig. 1 except for the green line, which represents the spectrum taken on 2014 October 4. The intensity and wavelength scales are in the same units as in Fig. 1.</figcaption></figure>

The forbidden lines of [O I] 5577, 6300 and 6363 Å in the spectrum of VES 723 show a constant position and very narrow profiles with a width of less than 0.5 km s⁻¹. This indicates their formation in the Earth’s ionosphere.

## 3.2 Diffuse interstellar bands and the multicomponent profile of the Na I D lines

At least three interstellar components are recognized in the Na I(1) line profiles (see Fig. 5). The component parameters for the 5889 Å line are listed in Table 2. Deciphering the components of the sodium lines in the 2011 spectrum is hampered by the presence of an emission component, which forms in the Earth’s ionosphere. The K I(1) 7699 Å line is split into three components with $V_r = -52, -29$ and $-8 \text{ km s}^{-1}$ (Fig. 5). Several components are also present in the narrow DIBs (e.g. 6269, 6379 and 6613 Å; see Table 3). However, spectra with a higher S/N are needed for a confident separation of these weak features.

The adopted systemic velocity for the star, $V_{\text{sys}} \sim -52 \text{ km s}^{-1}$, based on that of the local standard of rest ($V_{\text{LSR}} \sim -43 \text{ km s}^{-1}$) and the kinematic model of the Galaxy (e.g. Brand & Blitz 1993; Vallée 2008), indicates a distance of ~6 kpc to VES 723. This kinematic distance is in better agreement with the one based on the Gaia DR2 parallax rather than that from the EDR3 (see Table 4). According to Vallée (2008), for a distant star with the Galactic coordinates $l = 132^{\circ}4, b = +1^{\circ}1$, the longest-wavelength component forms in the local arm, the component at $V_r = -29 \text{ km s}^{-1}$ forms in the Perseus arm, while the shortest-wavelength component at $V_r = -52 \text{ km s}^{-1}$ forms in the outer (i.e. Cygnus) arm.

## 3.3 Temperature, luminosity and distance

Although no photospheric absorption lines have been found in our spectra, the emission-line content discussed above suggests some constraints on the temperature of the underlying star. In particular, the presence of He I lines and the absence of He II lines indicates an effective temperature ($T_{\text{eff}}$) between 20 000 K (e.g. Miroshnichenko 1996) and 28 000 K (e.g. Schmutz et al. 1991). Because the He I lines are strong, we assume that the star’s temperature is
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 4.** Parts of the 2017 August CFHT spectrum with permitted and forbidden lines of iron (left panel) and permitted lines of calcium, nitrogen and oxygen (right panel). The intensity scale is in the same units as in Fig. 1, and wavelengths are heliocentric.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Figure 5.** The multicomponent Na I 5889 Å line profiles in the spectra of VES 723 taken at different times. The blue line shows the 2011 January BTA spectrum, the green line shows the 2014 October BTA spectrum and the red line shows the averaged CFHT spectrum taken in 2017 August and September. The black line represents the K I 7699 Å line profile from the averaged CFHT spectrum. Emission components, which form in the Earth's ionosphere, are marked with dots. The intensity and wavelength scales are in the same units as in Fig. 1.</figcaption></figure>

<table><caption>**Table 2.** Heliocentric $V_r$ measurements for the multicomponent profiles of the Na I(1) and K I(1) lines in the spectra of VES 723.</caption><thead><tr><th></th><th colspan="3">Na I</th><th colspan="3">K I</th></tr><tr><th></th><th>(1)</th><th>(2)</th><th>(3)</th><th>(4)</th><th>(5)</th><th>(6)</th><th>(7)</th><th>(8)</th></tr></thead><tbody><tr><th>r</th><td>0.02</td><td>0.21</td><td>0.13</td><td>0.03</td><td>0.46</td><td>0.68</td><td>0.41</td></tr><tr><th>V<sub>r</sub></th><td>-53</td><td>-37</td><td>-27</td><td>-7</td><td>-52</td><td>-29</td><td>-7</td></tr></tbody></table>

*Notes.* Measured line parameters are shown in column 1. Relative intensities and $V_r$ of the Na I D line components are shown in columns 2–5. The same parameters for the K I line components are shown in columns 6–8.

<table><caption>**Table 3.** Average radial velocities and equivalent widths of the detected DIBs and their components in the spectra of VES 723.</caption><thead><tr><th>λ (Å)</th><th>V<sub>r</sub> (km s<sup>-1</sup>)</th><th>W (mÅ)</th></tr></thead><tbody><tr><td>5780.48</td><td>-50.5</td><td>0.42</td></tr><tr><td>5849.81</td><td>-49.0</td><td>0.03</td></tr><tr><td>6195.98</td><td>-52.4, -10.4</td><td>0.03, 0.08</td></tr><tr><td>6203.05</td><td>-56.2</td><td>0.08</td></tr><tr><td>6269.85</td><td>-49.3, -6.7</td><td>0.03, 0.03</td></tr><tr><td>6379.32</td><td>-46.9, -31.0</td><td>0.17, -</td></tr><tr><td>6613.62</td><td>-53.8, -30.0, -6.9</td><td>0.28, 0.14, 0.02</td></tr></tbody></table>

<table><caption>**Table 4.** Galactic parameters of VES 723 and MWC 17.</caption><thead><tr><th>Source ID</th><th>l; b</th><th>d, DR2 (kpc)</th><th>d, EDR3 (kpc)</th></tr></thead><tbody><tr><td>VES 723</td><td>132°4; +1°1</td><td>4.6<sup>+0.9</sup><sub>-0.6</sub></td><td>3.2 ± 0.3</td></tr><tr><td>MWC 17</td><td>129°8; -1°4</td><td>4.5<sup>+0.7</sup><sub>-0.6</sub></td><td>4.2 ± 0.6</td></tr></tbody></table>

*Notes.* The columns show the object's identification, the Galactic longitude and latitude, and the Gaia DR2 and EDR3 distances (in kiloparsec), respectively. The DR2 distances are taken from the catalogue of Brown et al. (2018), while the EDR3 distances are taken from the catalogue of Bailer-Jones et al. (2021). Relevant biases for conversion parallaxes into distances were taken into account in the referenced catalogues.

closer to the quoted upper limit, and we adopt $T_{\text{eff}} = 25\,000 \pm 2000$ K.

We use data from Green et al. (2019) on the spatial distribution of the interstellar matter near the Galactic plane to estimate the interstellar extinction in the direction of VES 723. For its Galactic coordinates (see Table 4), the interstellar reddening $E(g - r) \simeq E(B - V)$ reaches ~0.7 mag at a distance of 3–4 kpc and ~0.8 mag at a distance of 5–6 kpc. Alternatively, the reddening can be estimated by measuring equivalent widths of DIBs using calibrations by Herbig (1993) and Kos & Zwitter (2013). The noise in our spectra limits the accuracy of these measurements for weaker features, but the use of the strongest DIBs (e.g. at 5780 and 5797 Å) allowed us to derive an average colour excess of $E(B - V) = 0.9$ mag.

The results from both methods are roughly consistent with one another as well as with the reddening expected for the observed colour index $B - V = 0.7$ mag and the adopted $T_{\text{eff}}$. The latter estimate also suggests that the circumstellar reddening is small. Applying
<figure><img src="image_9.png" /></figure>

**Figure 6.** Left panel: spectral energy distributions of VES 723 (filled symbols) and MWC 17 (open squares). Both sets of data are shown corrected for the total (interstellar + circumstellar) reddening, $E(B-V) = 0.9$ mag for VES 723 and $E(B-V) = 1.5$ mag for MWC 17, using the average interstellar extinction wavelength dependence (Savage & Mathis 1979). Filled symbols represent photometric data from the following sources: circles (Fourth US Naval Observatory CCD Astrophysics Catalogue; Zacharias et al. 2013), squares (Two Micron All-Sky Survey; Skrutskie et al. 2006), upward triangles (*Wide-field Infrared Survey Explorer*, WISE; Wright et al. 2010), downward triangles (Midcourse Space Experiment; Egan et al. 2003), diamonds (*AKARI*; Ishihara et al. 2010) and stars (IRAS; Beichman et al. 1988). The same sources of information are used for the fluxes of MWC 17, but they are shown with the same symbol for an easy visual evaluation. The dereddened fluxes are scaled to that in the V band and shown on a logarithmic scale along with wavelengths in µm. The solid line represents a model atmosphere of a star with $T_{\text{eff}} = 25\,000$ K and $\log g = 4.0$ from Castelli & Kurucz (2003). Right panel: Hertzsprung-Russell diagram with positions of VES 723 based on the *Gaia* distances. The circle shows the luminosity derived using the DR2 distance, and the square shows the luminosity derived using the EDR3 distance. The uncertainties are discussed in the text. Evolutionary tracks for single rotating stars are taken from Ekström et al. (2012) and shown by solid lines along with the zero-age main-sequence location. Numbers by the tracks indicate initial masses in solar units.

a standard ratio of the total to selective extinction for hot stars, $R = 3.1$, we adopted a sum of the interstellar and circumstellar extinction of $A_V \sim 2.8$ mag.

The Balmer and He I line profiles shown in Figs 1 and 2 exhibit a small peak separation and even a narrow inner double-peaked structure in the $H\alpha$ profile, all suggesting a large inclination angle of the circumstellar disc with respect to the line of sight (Hanuschik et al. 1996; Silaj et al. 2010). Such a disc orientation can explain a low or even absent circumstellar reddening. At the same time, the absence of photospheric lines can be due to veiling by the free-free and bound-free continuum radiation from the circumstellar gas and emission components, which dominate the most prominent photospheric lines (e.g. H I, He I) expected for a star with the adopted $T_{\text{eff}}$.

We can estimate a lower limit of the object's luminosity. Using an average V-band brightness of $13.29 \pm 0.04$ mag from ASAS-SN and $A_V \sim 2.8$ mag along with the distance derived from the *Gaia* DR2 parallax (see Table 4), we can derive a visual absolute magnitude of $M_V \sim -2.8 \pm 0.5$ mag. The uncertainty is dominated by the parallax error with smaller additions from those of the extinction and average brightness. Applying a bolometric correction for *Teff* of 25 000 ± 2000 K (−2.5 ± 0.2 mag; Miroshnichenko 1997), we derive a luminosity of $\log L/L_\odot = 4.0 \pm 0.2$. The object's distance from the *Gaia* EDR3 is noticeably smaller and leads to $M_V \sim -2.0 \pm 0.2$ mag. This absolute magnitude corresponds to a luminosity of $\log L/L_\odot = 3.7 \pm 0.1$. The actual object's luminosity can be lower because of the contribution from the circumstellar continuum. Therefore, the *Gaia* DR2 distance along with the structure of the interstellar lines and the coincidence of the central positions of the narrow emission lines (see Figs 1 and 3) support the higher luminosity estimate.

The smaller distance derived from the *Gaia* EDR3 results can be attributed to the presence of a non-spherical circumstellar envelope around the object, which may affect the position of its photocentre. Nevertheless, it does not affect our conclusions on the object's nature.

A similar distance change between the DR2 and EDR3 data was derived for the emission-line star MWC 17, which is projectionally close to VES 723 (Table 4). The systemic velocity of MWC 17, $V_{\text{sys}} = -47$ km s⁻¹ (Klochkova & Chentsov 2016), is also more consistent with its location in the Cygnus arm, although this object shows a much stronger reddening, $E(B-V) \sim 1.5$ mag (see the left panel of Fig. 6).

## 4 DISCUSSION

Strong emission lines, such as $H\alpha$ and He I as well as the low-excitation forbidden lines of [N II], are among the defining features of objects with the B[e] phenomenon (Allen & Swings 1976; Thé, de Winter & Perez 1994). This phenomenon is characterized by the presence of an array of peculiar features, which include strong emission lines of neutral hydrogen and some other elements (e.g. Fe, Si) and forbidden lines (e.g. [O I], [Fe II], [N II]). Another defining feature is a large infrared excess because of the presence of circumstellar dust. However, objects with these features comprise a heterogeneous group.

The entire set of spectral features (e.g. $H\alpha$ and [N II] line profiles along with the presence of permitted and forbidden iron and nitrogen emission lines) makes VES 723 similar to the intermediate mass pre-main-sequence Herbig B[e] star MWC 297 (Drew et al. 1997; Zickgraf 2003), the massive B[e] supergiant MWC 137 (Kraus et al. 2017) and the B[e] supergiant binary system MWC 314 (Frasca et al. 2016), and to two objects whose B[e] phenomenon status is still debated, MWC 17 (Klochkova & Chentsov 2016) and CICam (e.g. Miroshnichenko et al. 2002; Barsukova et al. 2006). Therefore, spectral similarities only are not conclusive of the evolutionary status, especially in such complicated objects.

Balmer lines in the spectra of all the mentioned comparison objects are much stronger than in VES 723. MWC 297, MWC 137 and
MWC 314 are surrounded by extended nebulae illuminated by the central early B-type stars. The nebula around MWC 297 is a remnant of its protostellar cloud, while those in MWC 137 and MWC 314 are due to the stellar wind. MWC 17 and Cl Cam do not have visible nebulae around them despite very strong emission-line spectra.

MWC 17 has the closest set of properties to those of VES 723, because even the intrinsic spectral energy distributions of both objects are virtually the same (see Fig. 6). We note here that the shapes of the spectral energy distributions can be considered reliable, as, according to the ASAS-SN data, the photometric variability of both objects in the visual spectral region is very small. Therefore, we can expect a similar behaviour of the infrared fluxes, which were obtained at different times but within a relatively short period of ~10 yr.

The similarity of the optical spectra of VES 723 and MWC 17 shows up in the spectral line content and profile shapes. However, the spectrum of VES 723 has a smaller variety of lines. Similarly to MWC 17, we have found no photospheric lines in our spectra of VES 723. The absorption spectrum is represented by the interstellar Na I(1) and K I(1) lines as well as by DIBs.

Although VES 723 was mentioned in a study of star-forming regions as part of the W3 region (located at a distance of 2.3 kpc; Kraemer et al. 2003), it seems to be more distant from the Sun even with the EDR3 distance. Also, Kerton & Brunt (2003) found no association of the object with CO emission. This result indicates that VES 723 is not connected to a molecular cloud, thus ruling out its very young age.

Furthermore, our estimates of the fundamental parameters of VES 723 shown in the right panel of Fig. 6 suggest an initial star mass of ≥ 9 M☉, which is too high for a star to have an observable pre-main-sequence stage (Palla & Stahler 1993). Also, for the location at the zero-age main-sequence, VES 723 lacks a strong far-infrared excess typical of young stars (infrared flux flat or rising to wavelengths of ~100 µm; e.g. Verhoeff et al. 2012), which just emerged from their protostellar clouds (see Fig. 6, left panel). A strong decrease of the infrared flux longward of λ ~ 10 µm is a defining feature of FS CMa type objects with the B[e] phenomenon (Miroshnichenko 2007). This group is considered to comprise post-mass-transfer binary systems, whose circumstellar gaseous and dusty envelopes form during or after the Roche lobe overfilling phase. However, no signature of a secondary component has been found so far, leaving room for the suggestion that VES 723 could be a merger of a binary system. The latter was suggested as an alternative scenario for the nature of the FS CMa objects by de la Fuente et al. (2015).

## 5 CONCLUSIONS

The first high-resolution ($R \ge 60\,000$) optical spectra of the emission-line star VES 723 with an unknown evolutionary status were obtained at the 6-m telescope BTA and the 3.6-m CFHT in 2011–2017. Strong emission lines of H I, He I and [N II] dominate the spectrum. Broad foundations of the emission-line profile of H α and He I extend to ±250 km s⁻¹ from the line centres. Photospheric absorption lines have not been found in our spectra. Only multicomponent interstellar absorptions of Na I and K I, as well as several strongest DIBs, are present in them.

Based on our spectra of VES 723, we can conclude that there is a stationary position of the emission components of the H α line and a weak variability of the narrow features at its top. Such a stability confirms the line formation in a stable circumstellar medium. Only slight variations have been detected in the profile shapes and positions of some other lines. These variations are most noticeable in

the He I 5876 Å line (see the left panel of Fig. 2). The average $V_r$ of the [N II](1F) lines was adopted as the systemic velocity, $V_{sys} \sim -52$ km s⁻¹. The latter indicates that the object is located at a large distance of ~6 kpc, which agrees with the Gaia DR2 parallax.

Our estimates of the object's reddening and effective temperature along with the Gaia distance measurements suggest that VES 723 is an intermediate-mass star. It is unlikely to be a pre-main-sequence Herbig Be star or a B[e] supergiant. Currently, a more probable explanation of the observed properties is that the object is a member of the FS CMa group. A follow-up spectroscopic monitoring with a higher S/N in the continuum needs to be conducted to further constrain the nature of VES 723.

## ACKNOWLEDGEMENTS

We thank the referee, Dr Ian Howarth, for his useful suggestions on improving the clarity of the paper. This research has made use of the SIMBAD, SAO/NASA ADS, ASAS and Gaia data products as well as those from the WISE, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration; the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation; the Midcourse Space Experiment (MSX) Point Source Catalog; and the AKARI Infrared Astronomical Satellite All-Sky survey. This paper is partly based on observations obtained with the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique de France, and the University of Hawaii.

## DATA AVAILABILITY

The data underlying this article will be shared on reasonable request to the corresponding author.

## REFERENCES

* Allen D. A., Swings J. P., 1976, A&A, 47, 293

* Bailer-Jones C. A. L., Rybizki J., Fouesneau M., Demleitner M., Andrae R., 2021, VizieR Online Data Catalog, I/352

* Barsukova E. A., Borisov N. V., Burenkov A. N., Goranskii V. P., Klochkova V. G., Metlova N. V., 2006, Astron. Rep., 50, 664

* Beichman C., Neugebauer G., Habing H., Clegg P., Chester T., 1988, Infrared Astronomical Satellite (IRAS) Catalogs and Atlases. Vol. 1: Explanatory supplement. US Government Publishing Office, Washington, DC

* Brand J., Blitz L., 1993, A&A, 275, 67

* Brown A. G. A. et al., 2018, A&A, 616, A1

* Castelli F., Kurucz R. L., 2003, in Piskunov N., Weiss W. W., Gray D. F., eds, ASP Conf. Ser. Vol. 210, Modelling of Stellar Atmospheres. Astron. Soc. Pac., San Francisco, p. A20

* Chentsov E. L., Klochkova V. G., Miroshnichenko A. S., 2010, Astrophysical Bulletin, 65, 150

* Coyne G. V., MacConnell D. J., 1983, Vatican Observatory Publications, 1, 73

* de la Fuente D., Najarro F., Trombley C., Davies B., Figer D. F., 2015, A&A, 575, A10

* Donati J.-F., Semel M., Carter B. D., Rees D. E., Collier Cameron A., 1997, MNRAS, 291, 658
Drew J. E., Busfield G., Hoare M. G., Murdoch K. A., Nixon C. A., Oudmaijer
R. D., 1997, MNRAS, 286, 538

Egan M. P. et al., 2003, VizieR Online Data Catalog, V/114

Ekström S. et al., 2012, A&A, 537, A146

Frasca A., Miroshnichenko A. S., Rossi C., Friedjung M., Marilli E.,
Muratorio G., Busà I., 2016, A&A, 585, A60

Green G. M., Schlafly E., Zucker C., Speagle J. S., Finkbeiner D., 2019, ApJ,
887, 93

Hanuschik R. W., Hummel W., Sutorius E., Dietle O., Thimm G., 1996,
A&AS, 116, 309

Herbig G. H., 1993, ApJ, 407, 142

Ishihara D. et al., 2010, A&A, 514, A1

Kerton C. R., Brunt C. M., 2003, A&A, 399, 1083

Klochkova V. G., Chentsov E. L., 2004, Astron. Rep., 48, 1005

Klochkova V. G., Chentsov E. L., 2016, Astrophys. Bull., 71, 33

Klochkova V. G., Chentsov E. L., Miroshnichenko A. S., Panchuk V. E.,
Yushkin M. V., 2016, MNRAS, 459, 4183

Kochanek C. S. et al., 2017, PASP, 129, 104502

Kos J., Zwitter T., 2013, ApJ, 774, 72

Kraemer K. E., Shipman R. F., Price S. D., Mizuno D. R., Kuchar T., Carey
S. J., 2003, AJ, 126, 1423

Kraus M. et al., 2017, AJ, 154, 186

Manset N., Donati J.-F., 2003, Proc. SPIE, 4843, 425

Miroshnichenko A. S., 1996, A&A, 312, 941

Miroshnichenko A. S., 1997, in Bedding T. R., ed, Proc. IAU Symp. 189,
Fundamental Stellar Properties: The Interaction between Observation and
Theory. Kluwer, Dordrecht, p. 50

Miroshnichenko A. S., 2007, ApJ, 667, 497

Miroshnichenko A. S., Klochkova V. G., Bjorkman K. S., Panchuk V. E.,
2002, A&A, 390, 627

Miroshnichenko A. S., Manset N., Polcaro F., Rossi C., Zharikov S., 2011,
in Neiner C., Wade G., Meynet G., Peters G., eds, Proc. IAU Symp.
Voll. 272, Active OB Stars: Structure, Evolution, Mass Loss, and Critical
Limits. Kluwer, Dordrecht, p. 260

Miroshnichenko A. S. et al., 2020, ApJ, 897, 48

Palla F., Stahler S. W., 1993, ApJ, 418, 414

Panchuk V. E., Klochkova V. G., Yushkin M. V., 2017, Astron. Rep., 61, 820

Savage B. D., Mathis J. S., 1979, ARA&A, 17, 73

Schmutz W., Leitherer C., Hubeny I., Vogel M., Hamann W.-R., Wessolowski
U., 1991, ApJ, 372, 664

Silaj J., Jones C. E., Tycner C., Sigut T. A. A., Smith A. D., 2010, ApJS, 187,
228

Skrutskie M. F. et al., 2006, AJ, 131, 1163

Thé P. S., de Winter D., Perez M. R., 1994, A&AS, 104, 315

Vallée J. P., 2008, AJ, 135, 1301

Verhoeff A. P. et al., 2012, A&A, 538, A101

Wright E. L. et al., 2010, AJ, 140, 1868

Zacharias N., Finch C. T., Girard T. M., Henden A., Bartlett J. L., Monet D.
G., Zacharias M. I., 2013, AJ, 145, 44

Zickgraf F. J., 2003, A&A, 408, 257

This paper has been typeset from a TeX/LATeX file prepared by the author.