1 Introduction

StH$\alpha$ 190 has been independently discovered on objective prism plates by Kinman (1983, private communication to Whitelock et al. 1995, hereafter W95) and Stephenson (1986). Its symbiotic nature was noted during the spectroscopic survey of StH$\alpha$ objects by Downes & Keyes (1988). The 3300-9100 Å absolutely fluxed spectrum of StH$\alpha$ 190 included in the spectrophotometric atlas of 137 symbiotic stars by Munari & Zwitter (2001, hereafter MZ01) shows a well developed G-type continuum with minimal veiling by the nebular or hot companion continua and a pronounced emission line spectrum of moderate excitation (HeII missing) with strong [OIII] and [NeIII] forbidden lines. Minimal - if any - changes arise in the comparison with older available spectroscopy. The IUE spectrum of StH$\alpha$ 190 by Schmidt & Nussbaumer (1993, hereafter SN93) confirms the moderate excitation conditions (NV and HeII missing) and shows the photospheric continuum of an O sub-dwarf without contribution from nebular regions or an accretion disk.

Data from the Munari et al. (2001, hereafter MHZ) UBV(RI)$_{\rm C}$ photometric survey of symbiotic stars confirms a rather limited variability of StH$\alpha$ 190 and absence of outbursts since its discovery, reporting V=10.50, (B-V)=+0.84, (U-B)=-0.23, $(V-R)_{\rm C}=+0.50$ and $(V-I)_{\rm C}=+0.47$ for mid 2000. W95 infrared photometry of StH$\alpha$ 190 over 16 nights from Oct. 1983 to Jul. 1987 gives K=7.81, J-H=+0.57, H-K=+0.36 and K-L=+0.95 as mean values. In J and H bands W95 did not find evidence of variability while a modest $\bigtriangleup K = 0.16$ is attributed to changes in the heating of the circumstellar dust by the hot source.

In this Letter we report about the discovery of highly variable bipolar mass outflow and blob ejection from StH$\alpha$ 190, the first time in a yellow symbiotic star. Yellow SS harbour warm giants (F, G or early K type), which have much smaller dimensions and lower mass loss rates compared to the M giants of classical symbiotics. Jets and bipolar outflows have been so far discovered in only five other symbiotic stars (among the $\sim$225 known), all of them containing M giants or Miras and showing outburst activity: R Aqr (Burgarella & Paresce 1992), CH Cyg (Taylor et al. 1986), MWC 560 (Tomov et al. 1990), RS Oph (Taylor et al. 1989) and Hen 3-1341 (Tomov et al. 2000).

  

Table 1: Journal of spectroscopic observations and measured radial velocities. A= Asiago Echelle+CCD spectrograph operating at $R=18\,500$ resolving power, S = the SARG Echelle+CCD spectrograph at $R=57\,000$. The heliocentric radial velocities of HeI 5876 and [OIII] 4959 Å pertain to the main emission component, those of NaI to the stellar 5890-5896 doublet de-blended from the interstellar components. Data on H$\alpha$ includes heliocentric radial velocities of the main component (mc), the blue shifted jet ($b_{\rm J}$) and the red shifted jet ($r_{\rm J}$), as well as the component widths corrected for the instrumental PSF