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21 pages, 1509 KiB  
Article
Discovering New B[e] Supergiants and Candidate Luminous Blue Variables in Nearby Galaxies
by Grigoris Maravelias, Stephan de Wit, Alceste Z. Bonanos, Frank Tramper, Gonzalo Munoz-Sanchez and Evangelia Christodoulou
Galaxies 2023, 11(3), 79; https://doi.org/10.3390/galaxies11030079 - 19 Jun 2023
Cited by 2 | Viewed by 1448
Abstract
Mass loss is one of the key parameters that determine stellar evolution. Despite the progress we have achieved over the last decades we still cannot match the observational derived values with theoretical predictions. Even worse, there are certain phases, such as the B[e] [...] Read more.
Mass loss is one of the key parameters that determine stellar evolution. Despite the progress we have achieved over the last decades we still cannot match the observational derived values with theoretical predictions. Even worse, there are certain phases, such as the B[e] supergiants (B[e]SGs) and the Luminous Blue Variables (LBVs), where significant mass is lost through episodic or outburst activity. This leads to various structures forming around them that permit dust formation, making these objects bright IR sources. The ASSESS project aims to determine the role of episodic mass in the evolution of massive stars, by examining large numbers of cool and hot objects (such as B[e]SGs/LBVs). For this purpose, we initiated a large observation campaign to obtain spectroscopic data for ∼1000 IR-selected sources in 27 nearby galaxies. Within this project we successfully identified seven B[e] supergiants (one candidate) and four Luminous Blue Variables of which six and two, respectively, are new discoveries. We used spectroscopic, photometric, and light curve information to better constrain the nature of the reported objects. We particularly noted the presence of B[e]SGs at metallicity environments as low as 0.14 Z. Full article
(This article belongs to the Special Issue Theory and Observation of Active B-type Stars)
Show Figures

Figure 1

Figure 1
<p>Spectra of objects classified as B[e]SGs (including the B[e]SG candidate NGC7793-1). (Left) The full spectra for all stars with small offsets for better illustration purposes. The most prominent emission features are indicated. (Right) The region around H<math display="inline"><semantics> <mi>α</mi> </semantics></math> is highlighted to emphasize the relative strength of the emission compared to the continuum.</p>
Full article ">Figure 2
<p>Similar to <a href="#galaxies-11-00079-f001" class="html-fig">Figure 1</a>, but for LBVc. We note the lack of forbidden emission lines.</p>
Full article ">Figure 3
<p>The region between the [O <span class="html-small-caps">i</span>] and H<math display="inline"><semantics> <mi>α</mi> </semantics></math> line, that showcases multiple Fe <span class="html-small-caps">ii</span> emission lines. We note the clear presence of [O <span class="html-small-caps">i</span>] <math display="inline"><semantics> <mi>λ</mi> </semantics></math>6300 line for the B[e]SGs (left and middle panels, with the exception of the candidate NGC7793-1, due to the problematic spectrum; see text for more) and its absence from the LBVc spectra (right panel).</p>
Full article ">Figure 4
<p>The region around the [Ca <span class="html-small-caps">ii</span>] emission doublet. Its presence is evident in some B[e]SGs (left and middle panels, including NGC7793-1 candidate source, that suffers from data reduction artifacts due to slit overlaps), while LBVc (right panel) do not typically exhibit these lines (except for NGC55-3).</p>
Full article ">Figure 5
<p>The light curves from the Pan-STARRS survey for the B[e]SGs WLM-1 and NGC247-1. Each panel (per filter) shows the difference of each epoch from the mean value (noted on the y-axis label). See text for more.</p>
Full article ">Figure 6
<p>Same as <a href="#galaxies-11-00079-f005" class="html-fig">Figure 5</a>, but for the candidate LBVs NGC3109-1 and NGC247-2.</p>
Full article ">Figure 7
<p>(Left) The mid-IR <span class="html-italic">WISE</span> CCD for B[e]SGs and LBVs, including sources from the MCs (after [<a href="#B7-galaxies-11-00079" class="html-bibr">7</a>]) and our sample (for 5 out of 11 sources with <span class="html-italic">WISE</span> data). In general, the separation also holds for the new sources, with the exception of NGC55-1 (see text for more). (Right) IR CMD combining near-IR <span class="html-italic">J</span>-band (available for only five of our sources) with <span class="html-italic">Spitzer</span> [3.6]. We notice that, in this case, the newly found sources are consistent with the positions of the MC sources.</p>
Full article ">Figure 8
<p>(Left) The optical (<span class="html-italic">Gaia</span>) CMD, plotting BP–RP vs. M<math display="inline"><semantics> <msub> <mrow/> <mi>G</mi> </msub> </semantics></math> magnitude. We included all our sample and the MC sources from [<a href="#B7-galaxies-11-00079" class="html-bibr">7</a>] (except for two sources without a complete dataset in both <span class="html-italic">Gaia</span> and <span class="html-italic">Spitzer</span> surveys). (Right) The mid-IR (<span class="html-italic">Spitzer</span>) CMD using the IR color [3.6]–[4.5] vs. M<math display="inline"><semantics> <msub> <mrow/> <mrow> <mo>[</mo> <mn>4.5</mn> <mo>]</mo> </mrow> </msub> </semantics></math>. In this case, there is a significant improvement in the separation between the two classes. The position of NGC7793-1 favors a B[e]SG nature (see text for more).</p>
Full article ">Figure 9
<p>Similar to <a href="#galaxies-11-00079-f008" class="html-fig">Figure 8</a> but plotting the IR color [3.6]–[4.5] vs. the optical M<math display="inline"><semantics> <msub> <mrow/> <mi>G</mi> </msub> </semantics></math> magnitude. Similar to the IR CMD we saw relatively good separation between the two classes, with LBVs being brighter in the optical and less dusty compared to the B[e]SGs.</p>
Full article ">Figure 10
<p>The cumulative distribution function of the B[e]SGs and LBVs (including candidates) from this work and the literature. We notice (for the first time) the presence of B[e]SGs in lower metallicity environments and the fact that the two populations are not totally different (see text for more).</p>
Full article ">
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