----- Attempting Submission 2 (Wed Jun 01 00:52:50 GMT 2011) ----- The carbon star V Hydra is experiencing heavy mass loss as it undergoes the transition from AGB star to pre-planetary nebula. This is possibly the earliest object known in this brief phase, which is so short that few nearby stars are likely to be caught in the act. Molecular observations reveal that a bipolar nebula has been established even at this early stage. Using STIS, in Jan 2002, we discovered a high-velocity (> 200 km/s) jet or blob of gas in V Hya which had been ejected a few years prior from near the star. 2nd and 3rd epoch STIS observations over 2 years clearly revealed both its proper motion and strong deceleration. We propose STIS monitoring of this remarkable event over a period of 3 years, in order to obtain a precise dynamical and cooling history of this blob and any successor blobs that may have been ejected since then. This ejection event is likely to hold the key to understanding why initially spherical mass outflows adopt a bipolar geometry during the post-AGB phase of stellar evolution. The goal is to understand the interaction of the blobby jet outflow with the ambient circumstellar medium. We not only have the opportunity to look on as the circumstellar envelope is sculpted by this and perhaps other collimated mass ejections, but we also have an unprecedented chance to constrain the mechanism for mass ejection, and thereby help solve the long-standing puzzle of how the spherical mass-loss envelopes of AGB stars evolve into bipolar planetary nebulae.

We will utilise the same observing set-up as in GO 9800. We will use STIS with G430M (tilt setting of 4194) and the 52''$\times$0\farcs1 to obtain spectra in the $\lambda\lambda$4051-4337{\AA} range. From our previous data, the [SII]$\lambda$4066{\AA} line has a peak intensity of 4$\times10^{-13}$ erg s$^{-1}$ cm$^2$ {\AA}$^{-1}$ arcsec$^{-2}$. We will use somewhat larger exposure times ($\sim$720\,s) compared to GO\,9800 (520\,s total per slit position) to account for possible weakening of the blob brightness, using a 3 point dither along the slit, and CR-SPLIT=2, which gives us a S/N$\gsim$60-70 at peak of the [SII]$\lambda$4066{\AA} line, and a S/N$\gsim$15 at the continuum (which is roughly a factor 4 weaker in the -0\farcs1 slit, where the high-velocity outflow emission is strongest). This high S/N ratio is necessary because it allows us to measure the spatial offset of the peak from the source continuum to sub-pixel accuracy, which is important since the proper motion is about 0\farcs07 per year (and may decrease with time, if deceleration of the blob continues). In addition, we want to continue to be able to detect important fainter lines ([FeII]$\lambda$4241 \& 4285{\AA}) (which we have detected previosly) which provide additional probes of the physical conditions in the outflow. Since our most important objective is to understand the velocity field of the jets in order to study the collimation process, we will obtain spectra with 2 additional slit positions displaced symmetrically on either side of the central star (i.e. with offsets of $\pm$0\farcs1 and $\pm$0\farcs2). The G430M observations will require slightly more than 3.5 orbits. The remainder of the last orbit will be used for the observations of the ``central disk" in H$\alpha$, we will use a mosaic of 3 adjacent slit positions, using the 52''$\times$0\farcs1wide slit -- the narrow slit is used here (in contrast to the G430M observations) in order to obtain the highest spectral resolution because the velocity range covered by the ``disk" emission is much smaller (about 90\kms). The H$\alpha$ disk intensity at the half-power point is about 5$\times10^{-12}$ erg s$^{-1}$ cm$^2$ {\AA}$^{-1}$ arcsec$^{-2}$; we will use exposure times of 300 sec total per slit (CR-SPLIT=2 and a 3-point dither along slit) to obtain a S/N of 40 (after subtraction of the continuum background) -- such a high S/N is necessary to characterise the disk velocity structure with the limited spectral resolution (50\kms). Our slit mosaic will cover a total of 0\farcs3 across the central region -- such a mosaic is necessary because in our previous H$\alpha$ STIS observations, the disk was clearly seen only in the offset slits. The presence of the very strong stellar continuum in the central slit and imperfect rectification, resulting in very strong undulations along the wavelength direction -- makes it difficult to subtract the continuum, which is necessary in order to detect the weaker disk signal. We will use a 3-point dither strategy. The available windows for observing V Hya given our STIS slit ORIENT constraints (we require an ORIENT within $\pm$4\arcdeg~of the one in first two epochs) occur twice (1) in June/July, and (2) Dec/Jan/Feb each calendar year. We will request observing dates with an attempt to ensure that at least one epoch falls near (i.e. within a month) of maximum light, while a second one fall near minimum light of the 529 day period of this object. Such scheduling will allow us to check if there is any effect of the stellar light cycle on the outflow. COOL STARS 12 false 0.0 0.0 false false false false SUPPORTED STAR CARBON STAR J2000 10 51 37.2500 -21 15 0.32 J2000 STIS/CCD Spectroscopic No No G430M 4194 STIS/CCD Spectroscopic No No G750M 6581 STIS/CCD Spectroscopic No No G430M 4194 STIS/CCD Spectroscopic No No G750M 6581 STIS/CCD Spectroscopic No No G430M 4194 STIS/CCD Spectroscopic No No G750M 6581 POS-TARG MOSAIC DITHER 3 0.2 pattern should produce a mosaic of 3 slits, spaced apart by 0.2 arcsec, with a 3-point dither along the slit for each slit position; so 9 exposures STIS-ALONG-SLIT false true 0.22851 3 0.0 POS-TARG STIS-PERP-TO-SLIT 90.0 1 true POS-TARG MOSAIC DITHER 3 0.2 pattern should produce a mosaic of 3 slits, spaced apart by 0.2 arcsec, with a 3-point dither along the slit for each slit position; so 9 exposures STIS-ALONG-SLIT false true 0.22851 3 0.0 POS-TARG STIS-PERP-TO-SLIT 90.0 2 true POS-TARG DITHER 0.22851 LINE false false 3 90.0 STIS-ALONG-SLIT 3 false The scheduling data was generated by CASM 19.0. CASM was run in Phase II mode. /tmp/OPVisit1873973451571832563.xml 1306889253206 (Tic-Visit :proposal-id 12227 :visit-id "01" :proposal-version -1 :trans-version "20100902" :date "31-May-2011 17:47:31.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 755504 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12227 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12227 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2876 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12227 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3027 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12227 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3027 :al-overhead-at-end 75 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12227 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 2996 :al-overhead-at-end 0 :internal-dur-at-end 826 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) true 4 0 mosaic of 3 slits aligned along the outflow, spaced apart by 0.3 arcsec; for each slit position, a 3-point dither in steps of 0.225 arcsec mosaic of 3 slits aligned along the outflow, spaced apart by 0.2 arcsec; for each slit position, a 3-point dither in steps of 0.225 arcsec 9 exposures to produce a mosaic of 3 slits, spaced apart by 0.2 arcsec, with a 3-point dither along the slit for each slit position 9 exposures to produce a mosaic of 3 slits, spaced apart by 0.1 arcsec, with a 3-point dither along the slit for each slit position 9 exposures to produce a mosaic of 3 slits, spaced apart by 0.1 arcsec, with a 3-point dither along the slit for each slit position