Volume 567, July 2014
|Number of page(s)||13|
|Section||Stellar structure and evolution|
|Published online||09 July 2014|
The spectra of the new symbiotics stars are presented in Fig. A.1, and their fit files can be accessed from the CDS.
GTC spectra of the new IPHAS symbiotic stars. The region at 7600 Å with the strong oxygen atmospheric absorption band is not plotted.
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For the other 12 sources observed with the GTC telescope, spectra and SEDs reveal their nature as YSOs (Fig. B.1). In addition, one very compact planetary nebula, IPHASJ191942.91+162128.0, was also discovered. These 13 objects are listed in Table B.1 and their SEDs displayed in Fig. B.2. Their fit files can also be accessed from the CDS. The new planetary nebula IPHASJ191942.91+162128.0, which is discussed in some detail in Appendix C, is displayed at the top of Fig. B.2, whereas all other objects are shown to be young stars of different types (see Table B.1). Criteria for their spectral classification follow what was already discussed in Paper II.
Compared to both S- and D-type symbiotic stars (Fig. 2), the SED of YSOs are typically flatter, showing strong excesses beyond 12 μm. A 2000 K blackbody function is fitted to the 0.6 → 4.6 μm fluxes of the classical TTau star IPHASJ012539.29+613630.4 (bottom SED, blue solid curve) to illustrate this. The mid-IR colours are in this respect a very useful tool for distinguishing between symbiotic stars, YSOs, and other kinds of common mimics, such as compact planetary nebulae, even when lacking optical spectra, a fact that will be explored in detail in Paper IV.
Spectral energy distribution of non-symbiotic objects. Numbers in parentheses following the IPHAS names indicate the scale factors used for clarity in the figure. Errors are plotted when larger than the size of the symbols. See text.
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SIMBAD lists at this position an IRAS source (IRAS 19147+1615) detected at 25 and 60 μm. It coincides with an unresolved (size <42″) radio continuum source NVSS J191942+162128 with flux S(1.4 GHz) = 4.3 ± 0.5 mJy. The object is also included in the 2MASS, UKIDSS, WISE, and AKARI-IRC databases.
The IPHAS (Hα+[N ii]) and UKIDSS (H and K) images show that IPHASJ191942.91+162128.0 is moderately extended, with deconvolved FWHM of 1.2–1.3″. The UKIDSS H image, taken under excellent seeing conditions (0.6″), shows that the source is elongated in the NE-SW direction.
The SED of IPHASJ191942.91+162128.0 (not including the radio flux) is shown in Fig. B.2, and is rather different than those of YSOs and symbiotic stars, indicating that different contributors to the 1 → 60 μm emission are present: nebular continuum and line emission, dust with a broad range of temperatures, and possibly IR bands from molecules and other solid state features. This SED is typical of planetary nebulae.
Indeed, the optical spectrum of IPHASJ191942.91+ 162128.0 in Fig. B.1 corresponds to a low-excitation PN, showing a very weak continuum and strong emission lines of intermediate excitation ions. No He ii lines are detected. The strongest spectral lines are spatially resolved in the 2D GTC spectrum with deconvolved FWHM of 1.1 and 1.3″ in Hα and [N ii]6583 Å, respectively, i.e. in agreement with the values obtained from the images. Table C.1 lists the fluxes of the main emission lines measured in the spectrum.
The PN is heavily reddened, with AV = 7.3 mag, which is the weighted average obtained from the Hα, Hβ , and Hγ line ratios using the Fitzpatrick (2004) extincton law with RV = 3.1. The density is Ne([S ii]) = 5000 cm-3, and the temperature Te([N ii]) = 12 000 K. In spite of the relatively high electron density and small diameter, it is worth noting the absence in IPHASJ191942.91+162128.0 of the Ca ii infrared triplet and [Fe ii] emission lines typical of very young PNe (Viironen et al. 2009), indicating that the small apparent size is probably
due to a large distance to the object. Total abundances of He / H = 0.11, 12log (S) = 6.6, and 12log (O) = 8.7 were obtained using ICF = 1.13 and 1.0 for S and O, respectively (Kingsburgh & Barlow 1994). These values are typical of mainstream Galactic PNe (cf. Pottasch 1983).
IPHASJ191942.91+162128.0 is located at lII = 50.7°, bII = + 1.3°, i.e. towards the direction passing through the nearest end of the Galactic bar. Although its distance is undetermined with the data at hand, its size and chemical abundances are consistent with being a distant, relatively evolved PN located in the inner Galaxy near the extreme of the Galactic bar.
Observed line fluxes in IPHASJ191942.91+162128.0, normalized to Hβ = 100.
© ESO, 2014
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