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Register a new userNew Luminous Blue Variable Candidates in NGC 4736
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We have found three new LBV candidates in the star-forming galaxy NGC 4736. They show typical well-known LBV spectra, broad and strong hydrogen lines, He I lines, many Fe II lines, and forbidden [Fe II] and [Fe III]. Using archival Hubble Space Telescope and ground-based telescope data, we have estimated the bolometric magnitudes of these objects from -8.4 to -11.5, temperatures, and reddening. Source NGC 4736_1 (Mv = -10.2 +/- 0.1 mag) demonstrated variability between 2005 and 2018 as Delta V = 1.1 mag and Delta B = 0.82 mag, the object belongs to LBV stars. NGC 4736_2 (Mv < -8.6 mag) shows P Cyg profiles and its spectrum has changed from 2015 to 2018. The brightness variability of NGC 4736_2 is Delta V = 0.5 mag and Delta B = 0.4 mag. In NGC 4736_3 (Mv = -8.2 +/- 0.2 mag), we found strong nebular lines, broad wings of hydrogen; the brightness variation is only 0.2 mag. Therefore, the last two objects may reside to LBV candidates.
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We search for LBV stars in galaxies outside the Local Group. Here we present a study of two bright $Halpha$ sources in the NGC 247 galaxy. Object j004703.27-204708.4 ($M_V=-9.08 pm 0.15^m$) shows the spectral lines typical for well-studied LBV stars: broad and bright emission lines of hydrogen and helium He I with P Cyg profiles, emission lines of iron Fe II, silicon Si II, nitrogen N II and carbon C II, forbidden iron [Fe II] and nitrogen [N II] lines. The variability of the object is $Delta B = 0.74pm0.09^m$ and $Delta V = 0.88pm0.09^m$, which makes it reliable LBV candidate. The star j004702.18-204739.93 ($M_V=-9.66 pm 0.23^m$) shows many emission lines of iron Fe II, forbidden iron lines [Fe II], bright hydrogen lines with broad wings, and also forbidden lines of oxygen [O I] and calcium [Ca II] formed in the circumstellar matter. The study of the light curve of this star also did not reveal significant variations in brightness ($Delta V = 0.29pm0.09^m$). We obtained estimates of interstellar absorption, the photosphere temperature, as well as bolometric magnitudes $M_text{bol}=-10.5^{+0.5}_{-0.4}$ and $M_text{bol}=-10.8^{+0.5}_{-0.6}$, which corresponds to bolometric luminosities $log(L_text{bol}/L_{odot})=6.11^{+0.20}_{-0.16}$ and $6.24^{+0.20}_{-0.25}$ for j004703.27-204708.4 and j004702.18-204739.93 respectively. Thus, the object j004703.27-204708.4 remains a reliable LBV candidate, while the object j004702.18-204739.93 can be classified as B[e]-supergiant.
We study five Luminous Blue Variable (LBV) candidates in the Andromeda galaxy and one more (MN112) in the Milky Way. We obtain the same-epoch near-infrared (NIR) and optical spectra on the 3.5-meter telescope at the Apache Point Observatory and on the 6-meter telescope of the SAO RAS. The candidates show typical LBV features in their spectra: broad and strong hydrogen lines, HeI, FeII, and [FeII] lines. We estimate the temperatures, reddening, radii and luminosities of the stars using their spectral energy distributions. Bolometric luminosities of the candidates are similar to those of known LBV stars in the Andromeda galaxy. One candidate, J004341.84+411112.0, demonstrates photometric variability (about 0.27 mag in V band), which allows us to classify it as a LBV. The star J004415.04+420156.2 shows characteristics typical for B[e]-supergiants. The star J004411.36+413257.2 is classified as FeII star. We confirm that the stars J004621.08+421308.2 and J004507.65+413740.8 are warm hypergiants. We for the first time obtain NIR spectrum of the Galactic LBV candidate MN112. We use both optical and NIR spectra of MN112 for comparison with similar stars in M31 and notice identical spectra and the same temperature in the J004341.84+411112.0. This allows us to confirm that MN112 is a LBV, which should show its brightness variability in longer time span observations.
The hot massive luminous blue variables (LBVs) represent an important evolutionary phase of massive stars. Here, we report the discovery of a new LBV -- LAMOST J0037+4016 in the distant outskirt of the Andromeda galaxy. It is located in the south-western corner (a possible faint spiral arm) of M31 with an unexpectedly large projection distance of $sim$ 22 kpc from the center. The optical light curve shows a 1.2 mag variation in $V$ band and its outburst and quiescence phases both last over several years. The observed spectra indicate an A-type supergiant at epoch close to the outburst phase and a hot B-type supergiant with weak [Fe II] emission lines at epoch of much dimmer brightness. The near-infrared color-color diagram further shows it follows the distribution of Galactic and M31 LBVs rather than B[e] supergiants. All the existing data strongly show that LAMOST J0037+4016 is an LBV. By spectral energy distribution fitting, we find it has a luminosity ($4.42 pm 1.64$)$times 10^5$ $L_{odot}$ and an initial mass $sim 30$ $M_{odot}$, indicating its nature of less luminosity class of LBV.
We report the discovery of a new Galactic candidate Luminous Blue Variable (cLBV) via detection of an infrared circular nebula and follow-up spectroscopy of its central star. The nebula, MN112, is one of many dozens of circular nebulae detected at $24 mu$m in the {it Spitzer Space Telescope} archival data, whose morphology is similar to that of nebulae associated with known (c)LBVs and related evolved massive stars. Specifically, the core-halo morphology of MN112 bears a striking resemblance to the circumstellar nebula associated with the Galactic cLBV GAL 079.29+00.46, which suggests that both nebulae might have a similar origin and that the central star of MN112 is a LBV. The spectroscopy of the central star showed that its spectrum is almost identical to that of the bona fide LBV P Cygni, which also supports the LBV classification of the object. To further constrain the nature of MN112, we searched for signatures of possible high-amplitude ($ga 1$ mag) photometric variability of the central star using archival and newly obtained photometric data covering a 45 year period. We found that the B magnitude of the star was constant ($simeq$ 17.1$pm$0.3 mag) over this period, while in the I band the star brightened by $simeq 0.4$ mag during the last 17 years. Although the non-detection of large photometric variability leads us to use the prefix `candidate in the classification of MN112, we remind that the long-term photometric stability is not unusual for genuine LBVs and that the brightness of P Cygni remains relatively stable during the last three centuries.
We present the preliminary results of an image-subtraction analysis of the Galactic globular cluster M79 (NGC 1904), as well as a new investigation of the variable star population in NGC 1851. Both M79 and NGC 1851 have been previously associated with the Canis Major overdensity, which has been suggested to have an extragalactic origin. We found 6 new RR Lyrae in M79, and also recovered 3 previously known RR Lyrae. The average period of the 5 ab-type RR Lyrae is 0.68 ~ d, corresponding to an Oosterhoff II classification -- which is unusual, though not unprecedented, for systems of extragalactic origin. We also report on the discovery of at least 4 previously unknown variables in NGC 1851.
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