Hypergiant V1302 Aql in 2001-2014
Klochkova Valentina, Chentsov Eugene, Miroshnichenko Anatoly, Panchuk Vladimir, Yushkin Maksim
aa r X i v : . [ a s t r o - ph . S R ] D ec Hypergiant V1302 Aql in 2001–2014
V.G. Klochkova, ⋆ , E.L. Chentsov, A.S. Miroshnichenko, V.E. Panchuk, and M.V. Yushkin – Special Astrophysical Observatory RAS, Nizhnij Arkhyz, 369167 Russia – Department of Physics and Astronomy, University of North Carolina at Greensboro,Greensboro, NC 27402–6170, U.S.A.November 5, 2018 Abstract
We present the results of a study of spectral features and the velocity field in the at-mosphere and the circumstellar envelope of the hypergiant V1302 Aql, the optical counterpart ofthe IR source IRC+10420, based on high-resolution spectroscopic observations obtained in 2001–2014. We measured radial velocities of the following types of lines: forbidden and permitted pureemissions, absorption and emission components of lines of ions, pure absorptions (e.g., He i , Si ii ),and interstellar components of the Na i D–lines, K i , and DIBs. The heliocentric radial velocitymeasured for pure absorptions as well as for the forbidden and permitted pure emissions is closeto the systemic radial velocity and equal to V r = 63.7 ± ± ± − , respec-tively. Positions of the absorption components of the lines with inverse P Cyg profiles are stableand indicate the presence of clumps moving toward the star with a velocity of ∼
20 km s − . Theaverage radial velocity of the DIBs is V r (DIB) = 4.6 ± − . Comparison of the absorptionlines observed in 2001–2014 and those in earlier data shows no noticeable variations. We concludethat the hypergiant reached a phase of slowing down (or termination) of the effective temperaturegrowth and is currently located near the high-temperature boundary of the Yellow Void in theHertszprung-Russell diagramme. Key words. stars: massive, supergiants – techniques: spectroscopic – stars: individual: V1302 Aql
1. Introduction
The evolutionary status of a very luminous star V1302 Aql, the optical counterpart of the IR sourceIRC+10420, has been unclear. The variety of its properties allowed to classify it either as a Proto-Planetary Nebulae (PPN) [1] or as a very massive star that has passed through the red supergiantphase [2]. PPNe are currently thought to be low-mass peculiar supergiants with strong IR excessesin a short-term transition from the Asymptotic Giant Branch to the Planetary Nebula (PN) stage.They are descendants of intermediate-mass stars (initial masses 1–8 M ⊙ ) which have passed severalevolutionary stages, including switching energy sources and stages with typical mass loss rates upto 10 − M ⊙ yr − and even up to 10 − M ⊙ yr − . As a result, a PPN is a low-mass degenerate C–Ocore surrounded by a tenuous and usually an asymmetric envelope. As the core contracts, its effectivetemperature (T eff ) rises and the star moves blueward in the Hertsprung-Russell diagramme (hereafterHRD). This stage may last until T eff reaches ∼ ⊙ ∼ ≥
20 M ⊙ ) and the most luminous stars, ⋆ E-mail: [email protected]
Klochkova et al.: Hypergiant V1302 Aql in 2001–2014 which lose a significant part of their mass after leaving main-sequence, become red supergiants, andlater proceed to yellow supergiants. A typical luminosity of a yellow supergiant is log L/L ⊙ ∼ − − − M ⊙ yr − are sources of IR andmaser radiation as well as of numerous molecular emission lines. Nevertheless, the yellow hypergiant ρ Cas, nearest to V1302 Aql in HRD and possessing an extended and unstable atmosphere [7], showsno signs of circumstellar material [8].Obviously, depending on the adopted nature and hence luminosity of an object, its distance estimatemay differ by a factor of a few. However, data obtained during the last two decades from variousobservations leave no doubts that V1302 Aql is an object at the yellow hypergiant stage (see review byOudmaijer et al. [6]) as well as later papers [9, 10]. Moreover, V1302 Aql is now considered to be themost unambiguous massive Galactic object with a highest mass loss rate which undergoes a short-termevolutionary transition from a red supergiant to a Wolf-Rayet star [11]. One of the most compellingarguments confirming its high-luminosity massive star status has been derived from spectroscopicdata obtained at the 6 m telescope of the Russian Academy of Sciences, when the authors [12] found asignificant nitrogen excess in the atmosphere of V1302 Aql. In all the spectra obtained between 1997and 2000, a He i ≥
200 m˚A was detected. With the object’sT eff ∼ eff increase [12, 14, 15, 16] that allowed to suggest evolution toward the Wolf-Rayet stage. Humphreys etal. [17] points out that V1302 Aql is a post red supergiant star which is crossing a critical HRD regioncalled the Yellow Void [18].The T eff increase stimulates us to continue spectroscopic monitoring of this mysterious object. High-resolution spectroscopy is required to refine the structure and kinematics of its circumstellar envelope.The most adequate model to represent the observed kinematics is, in our opinion, the “rain” modelproposed by Humphreys et al. [17] even considering a bipolar model suggested later [10]. Observationswith a moderate spectral resolving power, R ∼ et al. [17] to testthe model. We obtained spectra with a much higher resolution (up to R ∼
2. Observational Data
We have added 16 new spectra to our collection of the V1302 Aql data in 2001–2014. The observingdates and data spectral ranges are listed in the first two columns of Table 1. Most spectra were obtainedwith the ´echelle spectrograph NES with spectral resolution R = 60000 [19, 20]. Our first spectrumobtained on 2001 August 9 was taken with the spectrograph LYNX 1K ×
1K CCD, R ∼ ECHELLE context in
MIDAS modified to features of the spectrographs used (see details in [22]). Cosmic particles were removed bymedian averaging of two consecutive spectra. Wavelength calibration of the spectra was derived usinga Th-Ar hollow cathode lamp.One of the spectra used in this paper was obtained at the McDonald Observatory on 2009 September11 with the ´echelle spectrograph TS2 R = 60000 [23] in the coud´e focus of the 2.7 m Harlan J. Smithtelescope. This allowed us to fill the gap in observations with the 6 m telescope for 2009. One-dimensional data for this spectrum were extracted using the apall task within the echelle packagein IRAF. In particular, the spectral range of this observation allowed us to study profiles of the stronglines of Ca ii lochkova et al.: Hypergiant V1302 Aql in 2001–2014 Table 1.
Averaged heliocentric velocities for groups of lines in the spectra of V1302 Aql.
Date ∆ λ , V r , km s − nm Emissions Em/Abs Absorptions ISperm. forb. Fe ii , etc. Si ii +He i H α +H β Na I D DIB09.08.01 510–670 65 68 36/79 61 68 – 5.628.08.04 530–680 67 61 43/83 68 69 11.3 4.824.11.07 530–680 65 61 42/77 58 68 11.2 4.513.07.08 520–670 65 65 42/79 54 67 11.2 5:18.08.08 460–600 66 65 45/80 60 70 11.0 5:3 & 5.11.08 450–590 64 60 46/85 71 72 11.0 4.411.09.09 420–880 64 60 39/82 66 69 10.6 3:31.07.10 440–590 66 59 42/80 60 74 10.8 5:20.11.10 400–550 64 – 43/80 – 70 – –3 & 8.08.12 430–680 65 62 37/81 70 72 10.6 4.427.05.13 430–670 64 61 40/81 65 73 10.5 4.819.08.13 430–670 66 61 35/80 64 72 10.3 5.209.10.13 430–670 66 61 37/82 67 72 10.8 4.613.08.14 430–670 66 62 38/83 63 72 11.1 4.204.10.14 540–850 65 62 – 65 70 10.5 4:Average values of V r , km s − ± ± ± . / . ± . ± ± ± The remaining part of the data reduction, including measurements of the lines intensities andpositions, was done with the latest version of the DECH20t package [24]. This package, traditionallyused in our studies, permits radial velocity measurements for individual features of complex lineprofiles. Only heliocentric radial velocities, V r , are used throughout this paper. Their systematic errorsdo not exceed 1 km s − for a single line. The latter can be seen in the last column of Table 1, whereV r of the saturated interstellar components of the Na i D–lines are listed. Features in the spectrum ofV1302 Aql were identified using an earlier published atlas [25].
3. Results and Discussion
Earlier spectroscopic observations of V1302 Aql revealed a gradual transition from a normal F–typesupergiant [26] to an A5–type one [14]. The new spectral type estimates for 2001–2014 based on ourtechnique presented in [12, 14] give the following results. Pure absorption lines in the blue part of thespectrum indicate a spectral type A6, while inclusion of criteria using He i and Si ii absorptions leadsto A3.5. Therefore we conclude that the current spectral type coincides with that derived in [12, 14]within the uncertainties and that the objects T eff does not grow anymore. As earlier, line profiles in the spectra of V1302 Aql vary from purely absorption with small deviationsfrom symmetry to P Cyg–type profiles and double-peaked emissions. Examples of these line profilesare shown in Fig. 1. Variations of the intensities and profiles for the last 20 years taking into accountresults from [12, 14, 17] are noticeable but small.Hydrogen lines H α and H β in 2001–2014 still have a characteristic double-peaked profile, which wasobserved in the 1990’s see Fig. 5 in [14]. Positions of both emission peaks and the central depressionhave not changed since then. Variations of the residual intensities of the emission components of bothlines remained within 40%. The H α profiles in two spectra are shown in Fig. 2.A typical peak intensity ratio for the entire 20-year long period is seen in the spectrum taken in2014. An unusual H α line profile, when the red peak is significantly stronger than the blue one, is Klochkova et al.: Hypergiant V1302 Aql in 2001–2014 r a b cd Figure 1.
The line profile transformation in the spectra of V1302 Aql in 2012–2014. From top to bot-tom: a) the forbidden emissions [Fe ii ] (Multiplet 14F) 7155 ˚A and [O i ] (1F) 6300 ˚A; b) the emissionsFe ii (46) 5991, 6084, and 6113 ˚A and an average of the Fe i (168) 6394 ˚A and Ti ii (112) 6718 ˚A; c)the emission Fe ii (74) 6417 ˚A an average of the emissions Cr ii (50) 5502 ˚A and 5511 ˚A and absorp-tion/emission lines Ti ii (69) 5337 ˚A and Ti ii (70) 5154 ˚A d) the absorptions Si ii (5) 5056 ˚A and Si ii (2) 6347 ˚A. The vertical line shows the systemic velocity V sys ∼
60 km s − [15].detected in only one spectrum taken on 2007 November 24. In all other spectra the peak intensity ratiois the opposite [14, 17]. Variations of the residual intensities of the strongest forbidden and permittedFe ii lines are even weaker (within 10%). In the last 7 spectra taken in 2012–2014 they are limited to20% and 6%, respectively. According to [15], the average radial velocity of several rotational bands of the CO molecule withrespect to the local standard of rest is V(LSR) = 77 km s − . The heliocentric systemic radial velocityof the object is V sys ∼
60 km s − . Humphreys et al. [17] determined V sys = 58 −
60 km s − using acombination of CO and OH bands. We note that the latter is also close to the velocities derived fromradio lines of other molecules (see [28] and references therein).The relative stability of the spectrum of V1302 Aql in recent time and homogeneity of the obtainedmaterial allowed us to move from reporting the variety of the spectral line shapes to following a lochkova et al.: Hypergiant V1302 Aql in 2001–2014 -200 0 200 Vr, km/s02468r Figure 2.
The H α line profile in the spectra of V1302 Aql in 2007 and 2014. The vertical line showsthe systemic velocity V sys ∼
60 km s − [15].gradual transformation between different shapes. Comparison of Figs. 1 and 3 with the data fromTable 1 convinces that such a transformation is real. The profiles shown in Fig. 1 are averaged fromthe spectra taken in 2012–2014. A typical example of relationships between the radial velocities forindividual lines and their residual intensities is shown in Fig. 3. The same profile types follow eachother from top to bottom in Fig. 1 and from left to right in Fig. 3 and in Table 1.Variations of the average radial velocities of various line groups (see Table 1) are small as well. Inparticular, all the radial velocities for the pure absorptions are in a range of 54–70 km s − . Forbiddenlines are asymmetric (see Fig. 1a), such as the peak intensity is red-shifted with respect to the lowerpart of the profile by 6 km s − on average. The [Ca ii ](1F) 7291 and 7324 ˚A emissions seen in ourspectra taken on 2009 September 11 and 2014 October 4 are much stronger that all other forbiddenlines but with no positional shift with respect to the latter. Radial velocities of the entire profiles andtheir peaks are presented in Fig. 3a by circles and dots, respectively. The averaged radial velocities,measured from lower parts of the forbidden line profiles, are listed in column 3 of Table 1.Permitted emissions of the iron group are noticeably wider than the forbidden lines. For example, atthe same residual intensity of 1.5, the half-widths at the zero level are 70 and 50 km s − , respectively.The iron lines are clearly double-peaked with a weaker blue-shifted peak (see Fig. 1b). The radialvelocities of the lower parts of these emission profiles (in the same way as for the forbidden lines), areshown in column 4 of Table 1 and represented by circles in Fig. 3b. The emission peak velocities areshown by dots in the same Figure. The peak separation decreases from 50 km s − for weak emissionsto 26 km s − for the strongest ones, where it even reaches a triangular shape. It seems that the double-peaked profiles are not just a sum of two narrower single-peaked emissions separated by 50 km s − ,but that a partially filled absorption component formed in the stellar atmosphere also takes part inthe overall profile formation.It is seen in Figs. 1bc that a gradually deepening absorption “pushes down” the central part of theprofile and eventually turns it into an inverse P Cyg–type profile. Line profiles may have this kind ofshape in the following cases: when a narrow circumstellar absorption overlaps with a wide circumstellaremission or when two narrower emissions with different radial velocities join together. The inner slopeswould be shallower than the outer ones in the latter case. We observe steeper inner slopes instead,therefore the emission components are separated by an absorption. It is possible to have a combinationof these two formation mechanisms as well as a double–ray version suggested in [10].There a many lines with emission components on both sides of the absorption in the spectrum ofV1302 Aql. We include in the group of lines with an inverse P Cyg–profile those with the continuumabove the absorption core, r <
1. If the central depression is seen at r >
1, the line is considered to havea double-peaked profile. Column 5 of Table 1 contains the average radial velocities for blue-shifted
Klochkova et al.: Hypergiant V1302 Aql in 2001–2014
Vr a b c d re αβγ Figure 3.
The relationships between the heliocentric radial velocities and residual intensities of theline components in the spectra of V1302 Aql on 2008 August 3 and 8. The horizontal dashed lineshows the systemic velocity V sys ∼
60 km s − [15]. a) Forbidden emissions (whole profiles are shownby filled circles, while their peaks are shown by dots). b) Permitted double-peaked profiles (symbols arethe same as in part a). c) Lines with inverse P Cyg–profiles (emission and absorption components areshown by filled circles, while cores of the strongest absorptions are shown by dots). d) Fe ii absorptions(whole profiles are shown by circles) and He i and Si ii absorptions (whole profiles are shown by opencircles, cores are shown by dots). e) Absorption components of the H i lines (symbols are the same asin part d).emission and absorption components in the group of lines with P Cyg–profiles. Both such componentsare shown by circles in Fig. 3c (an absorption asymmetry is shown for the strongest ones). The red-shifted components are weaker ( r < ±
10 km s − in our spectra.The profiles in Fig. 1 differ from classic P Cyg–profiles which represent a spherically-symmetricenvelope with a radial velocity gradient. The latter show a relationship between the emission compo-nent intensity and the absorption component depth. However the weakest absorptions in our profiles( r < < r < r ∼ r < ii (37,38), Ti ii (31), Cr ii , may have hidden outside emissioncomponents, because their wings are narrower than those of Si ii and Mg ii with similar depths. Fig. 3dshows the uncertain absorption group members by filled circles, while more reliable ones are shownby open circles. In turn, we consider the most pure absorptions are the weakest ones, such as Si ii (4,5) and He i σ ≤ − and σ = 0.2 km s − for the interstellar features.Closeness of the radial velocities seen in Fig. 3 is noticeable in the following line groups: – iron absorption lines in the blue part of the spectrum and absorption components of the lines withinverse P Cyg–profiles (averaging all our data gives 81 and 80 km s − , respectively). We considerstable positions of the latter as an indicator of a matter infall; – strong Si ii (2) absorptions (they are shown by a pair of open circles in Fig. 3d) and absorptioncomponents of the H α and H β lines (average radial velocities are 73 and ∼
70 km s − , respectively); – the weakest absorptions and forbidden emissions (63.7 and 65.2 km s − , respectively). Since theformer form in the deepest layers of the photosphere (or pseudo-photosphere) while the latter formin an extended envelope, it is natural that the radial velocity of the latter is the closest to that ofthe star’s center of mass, i.e. V sys ∼
60 km s − . lochkova et al.: Hypergiant V1302 Aql in 2001–2014 Vr, km/s r Figure 4.
The Na i D1 line profile in the spectra of V1302 Aql (thick solid line) and HD 183143 (dashedline). The thin solid line shows the profile of the K i (1) 7665 ˚A line in the spectrum of V1302 Aql.The dotted line shows the Fe ii
4. Interstellar features in the spectrum of V1302 Aql
Fig. 4 shows a complex profile of the D1–line of a resonance Na i doublet. The mail part of its absorptioncomponent forms in a cold interstellar gas in the line of sight, while a weaker red-shifted componentforms in the atmosphere of V1302 Aql. The latter is well reproduced by the absorption component ofthe Fe ii i D–line profile in a range of V r = − − +50 km s − has interstellarnature. As follows from a recent compilation of the data on the structure and kinematics of the MilkyWay [27], radial velocity in the direction of V1302 Aql increases with distance and reaches +50 km s − at a distance D = 5.3 kpc. Fig. 4 shows the Na i D1–line profile in the spectrum of the B–type hypergiantHD 183143, which is projectionally close to V1302 Aql (the Galactic coordinates l/b = 53 . ◦ / . ◦ . ◦ / − . ◦
5, respectively). However, as seen in Fig. 1 in [28], HD 183143 is located between the localand Carina–Norma spiral arms, while the line of sight to V1302 Aql passes through the latter armbetween 3 and 8 kpc. Therefore, a distance toward HD 183143 is ∼ i absorption andthe maximum of above mentioned V r (D) relationship indicates that V1302 Aql cannot be closer than5.3 kpc. Its spectroscopic parallax moves it even further away to 6.5–8.0 kpc.The K i i D–lines andsplit into three components. The weakest of them at V r ∼ −
10 km s − corresponds to the blue-shiftedcomponent of the Na i D1 line (Fig. 4), while the other two at V r ∼ − are merged in theNa i profile. The stellar absorption component is located at V r ∼
84 km s − . As clearly seen in Fig. 4,the K i r ∼
84 km s − indicatesthat it forms in the circumstellar envelope.Using our large high-quality material, we measured positions of some diffuse interstellar band (DIB).A list of those reliably identifiable in the spectrum of V1302 Aql was published in [25]. Note twoimportant points concerning the search and measurement of the DIB positions: – the number of DIBs with measured V r varies from one spectrum to another (from 5 to 17 features); – the individual DIBs V r differ systematically.The latter was mentioned by Oudmaijer [16], who has identified many DIBs in the object’s spectrum.Over 30 of them are narrow and have equivalent widths of ≥
20 m˚A. The author explained a large scatterof the measured V r (from 5 to 40 km s − ) by uncertain DIB wavelengths. Klochkova et al.: Hypergiant V1302 Aql in 2001–2014
The last column of Table 1 lists average V r for each of the observing dates in 2001–2014 of a smallgroup of the narrowest and most symmetric DIBs which show the smallest differential shifts. Theirstandard wavelengths (5796.97, 5849.82, 6195.96, 6376.00, and 6379.24 ˚A) are taken from [30]. Aftersuch a selection, the average V r for all the dates came to 4.6 ± − .
5. Closest analogs of the hypergiant V1302 Aql
In Sect. 1 we mentioned ρ Cas, a well-studied yellow hypergiant with a luminosity similar to thatof V1302 Aql. In particular, optical spectra of ρ Cas and a complex structure of its atmosphere andenvelope have been recently studied in detail [7, 31]. However if all features are taken into account,the optical counterpart of the IR-source IRAS 18357 − − ∼ − i , N i , Fe i , Fe ii , Ti ii , [Fe ii ], etc. According to these authors, lineprofile features of IRAS 18357 − i , Ca ii ,and N i in the spectrum of IRAS 18357 − eff . The same authors studied kinematic properties of the star’s atmosphereand envelope in detail and noted signs of a matter infall onto the star with a speed of 30 km s − .Later, based on a set of optical spectra of HR 8752 obtained with various instruments in 1973–2005,Nieuwenhuijzen et al. [35] have analysed these data using a homogeneous approach. Adding data fromeven a longer photometric monitoring, they restored temporal variations of the star’s fundamentalparameters, such as T eff , luminosity, radius, color-index B − V , etc. One of their main results is aconclusion about a gradual growth of T eff from log T eff = 3.65 circa 1900 to log T eff = 3.90 in 2000.Therefore, HR 8752 is the closest analog of V1302 Aql based on all features. At the same time, HR 8752seems to have a lower mass compared to that of V1302 Aql judging on the HRD position [35].Comparison of the spectral line profiles in our spectra of V1302 Aql in 2001–2014 indicates theabsence of a noticeable spectral variability, thus allowing to conclude that the hypergiant entered aphase of a slow down (or termination) of the T eff growth and approached the Yellow Void boundary,which is called the White Wall [10]. Earlier authors [36] suspected stabilization of the star’s T eff basedon a long-term photometric monitoring. New evolutionary loops may follow this episode, such as thatobserved for HR 8752 on a timescale of 10 years [18]. Therefore, it seems very important to continuemonitoring of V1302 Aql.
6. Conclusions
Using a set of high-resolution spectra of V1302 Aql obtained in 2001–2014, we measured intensitiesand positions of various spectral features that allowed us to analyse the profile behaviour with timeas well as the velocity field in various layers of the object’s extended atmosphere and its circumstellarenvelope. We concluded on a closeness of the V r for the iron absorption lines in the blue spectral partand absorption components with inverse P Cyg–profiles. Positions of the latter features that reflectsclumps falling onto the star with a velocity of ∼
20 km s − has been stable for all the observing dates.The position of the strong Si ii (2) absorptions and absorption components of the H α and H β linesvaried insignificantly around 63.7 and 70.5 km s − , respectively.The V r for the weakest absorptions, which form in the deepest observable photospheric (or pseudo-photospheric) layers, and for the forbidden emissions, which form in an extended envelope (63.7 and65.2 km s − , respectively). The average V r of the permitted emissions also weakly deviates from that lochkova et al.: Hypergiant V1302 Aql in 2001–2014 of the pure absorptions. It is equal to 62.0 km s − for all the observing dates. The average V r of theinterstellar features is equal to 4.6 ± − .Comparison of the features in the spectra of V1302 Aql in 2001–2014 indicates the absence of anoticeable variability. We conclude that the hypergiant entered a phase of a slow down (or termination)of the T eff growth and approached the high-temperature boundary of the Yellow Void. Acknowledgments
This study was accomplished with a financial support of the Russian Foundation for Basic Research(RFBR) in the framework of the project No.14–02–00291 a. A.M. acknowledges support of his travelto the McDonald Observatory from the Department of Physics and Astronomy of the University ofNorth Carolina at Greensboro. We have made use of the astronomical data bases SIMBAD and ADS.
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