Wolf 1465: Not a Bright Dwarf Carbon Star

Dwarf carbon (dC) stars objects with prominent C2 bands in their spectra, but luminosity near the main sequence pose a variety of interesting problems. The long-standing presumption is that the carbon must have been transferred from a now invisible companion (Green 2013), but empirical evidence to this effect has been elusive. Data that many, most or possibly all dC stars are binary, a concept suspected but unproven for decades, is finally starting to emerge from recent photometric (Margon et al. 2018), spectroscopic (Whitehouse et al. 2018) and astrometric (Harris et al. 2018, hereafter “H18”) observations. A remaining important issue, however, is metallicity. As yet only one dC star has a detailed abundance analysis, the prototype dC, G77-61, and it is extraordinarily metal poor, [Fe/H] = −4 (Plez & Cohen 2005). Clearly a far larger sample is needed to probe this interesting abundance result, but even the brightest dCs (V ∼14) require the largest telescopes for these analyses. Thus discovery of a previously unnoted very bright dC would be quite important. Recently H18 have noted that (I−J), (J−Ks) colors provide excellent segregation of dC stars from normal late-type dwarfs, and the 2MASS colors for the high proper motion star Wolf 1465 ( = LHS 466, = LFT 1419, = LTT 7381, = G 155-27) fall in the dC regime. They point out that at V = 13.7 (Harrington & Dahn 1980), this would make Wolf 1465 the brightest known dC, exceeding even the prototype G77-61. The recent Gaia DR2 parallax of 17 mas might also make it the closest such star. However, H18 note an important caveat: the UKIDSS colors disagree with 2MASS by 0.2 mag, indicating one of the measures is likely in error. The MV = 9.85 derived from the parallax is compatible with either a late type dwarf or a dC, so sheds no further light on the mystery. Although Wolf 1465 first appeared in the literature almost a century ago (Wolf & Reinmuth 1925), and there are multiple astrometric measurements published, there is little published spectral data. Rodgers & Eggen (1974) obtained but did not display a photographic spectrum, with the notation “slightly weak lined”, which is typed as K4 by Augensen & Buscombe (1978). Bidelman (1985) cites an unpublished photographic spectrum by G. P. Kuiper obtained years earlier, assigning spectral type K5. We are aware of no publication of an actual spectrogram, nor any reported observation since the use of solid state detectors became common. To gain a definitive modern classification of Wolf 1465, we obtained the spectrum of the star on 2018 May 8 UT, using the Kast spectrograph of the Lick Observatory Shane telescope. The resulting 800 s exposure is shown in Figure 1; the spectral resolution is about 2.5 Å. Although the modest resolution is not ideal for precise classification purposes, it is clear that Wolf 1465 is a normal mid-K star, in agreement with the unpublished photographic spectrograms of decades earlier. Prominent Ca lines (IR triplet, λλ4226, 6162, H&K), NaD, and the Mg b band are present, but negligible Balmer or TiO absorption, bounding the classification on the warm and cool ends, respectively. There is certainly no sign of C2 features. The MV = 9.85 derived from the parallax supports the interpretation as a dK star. It seems likely that H18's suggestion that the 2MASS photometry is flawed is correct. Given the high proper motion of the star, 1260 mas yr−1, it may even be possible that the object was misidentified there by an automated algorithm. Unfortunately Wolf 1465 is not the brightest dC star, and the original prototype from four decades past, G77-61 (Dahn et al. 1977), continues to hold this distinction.