V1025 Tau and its Associated Reflection Nebula
by Zaytsev and Hanson
Click for larger image
Herbig Ae/Be variable star V1025 Tau [1, 2] with its associated reflection nebula GN 04.32.8 reflection nebula [3] embedded into a sub-region of the Taurus Molecular Cloud is the brightest component of a young star group surrounding a variable star V* HP Tau [4] in which group the V1025 Tau itself is identified as CoKu (Cohen+Kuhi) HP Tau/G2 and other two components are CoKu HP Tau/G1 [5] and CoKu HP Tau/G3 [6]. According to the GCVS variability classification scheme [7] the CoKu HP Tau/G2 is an Orion type variable (“irregular, eruptive variables connected with bright or dark diffuse nebulae or observed in the regions of these nebulae”) located at a distance of about 161 pc as measured by VLBA using the direct parallax method [8, 9], at which distance the edge of the image frame corresponds to 2.7 ly = 169 kAU. Manually annotated cropped view to the central part of the image at 100% original resolution is shown below in Fig. S1.
Fig. S1. Manually annotated image of the V1025 Tau and its immediate surroundings.
The CoKu HP Tau/G2 and CoKu HP Tau/G3 are believed to form a gravitationally bound system according to [8, 9] and on top of that both V* HP Tau and CoKu HP Tau/G3 were confirmed to be tight binaries by themselves based on lunar occultation data analysis under [10, 11] and the orbital solution for HP Tau/G3 can be found in [12, 13]. Thus, the CoKu HP Tau/G2 plus CoKu HP Tau/G3 system appears to be a hierarchical triple star system [8, 9]. Furthermore, treating the V* HP Tau plus CoKu HP Tau/G2 plus CoKu HP Tau/G3 as a wide triple system (intentionally neglecting tightly coupled components of V* HP Tau and CoKu HP Tau/G3) [14, 15] gives masses for its components as 0.94, 2.49, 0.72 Solar masses correspondingly, with separation between CoKu HP Tau/G2 and V* HP Tau determined to be 3089 AU and separation between CoKu HP Tau/G2 and Coku HP Tau/G3 determined to be 1463 AU. The age of these three stars is estimated to be in the range of only 3-8 Myr, with CoKu HP Tau/G3 being the youngest and CoKu HP Tau/G2 - the oldest in the group [8, 9].
The reflection nebula surrounding the HP Tau group consists of multiple concentric fronts of which the brightness drops and average radial width - increases as they move away from the central CoKu HP Tau/G2 (V1025 Tau) star. The curvature diameter of the smallest curved front features visible in the core of the nebula is about 0.043 ly = 2735 AU based on the estimated distance to the star from above. Another set of non-concentric fronts exists here as well, some of which seemingly associated with V* HQ Tau star located 5 arc.min away from HP Tau/G2 in the lower right part of the image frame. Many of the fronts are with peculiar 120 deg bends and junction points. The entire set of fronts is embedded in a dark cloud showing hints of an even more peculiar spiral structure reaching out to the edge of the frame. Simple attempt to fit the most prominent curved fronts in the central part of the image with circular shells centered (or nearly centered) on the stars belonging to the HP Tau group and the nearby stars visible in the FOV is given below in Fig. S2. Interestingly enough, some of those fit rather well (each circle is provided with the indicator of a center). Further study is needed to attempt a 3D reconstruction of this region and its relation to the Taurus Molecular Cloud situated in the range of distances between 130 and 160 pc according to [16, 17], so the V1025 Tau is actually expected to sit behind most of the structures of that dark cloud.
Fig. S2. Attempt to fit the curved fronts visible in the central part of the reflection nebula surrounding V1025 Tau with circular shells centered (or nearly centered) on the stars belonging to HP Tau group and other nearby stars.
Data and initial calibration/integration: Alexandr Zaytsev https://www.astrobin.com/users/m57ring/
ASA Ritchey-Chretien RC-1000: D=1m, f/6.8 on alt-azimuthal direct drive fork mount, FLI ProLine 16803 with secondary mirror based motorized focusing and automatic de-rotation (Telescope #1 system of ChileScope observatory, Río Hurtado Valley, Chile).
16x L + 8x R + 8x G + 8x B guided 1200 sec exposures (13h 20min of combined integral) collected over 7 imaging sessions carried out on Dec 8, 9, 10 of 2023 and Jan 4, 5, 6, 7 of 2024 using Chilescope Telescope #1 system.
Image Processing: Mark Hanson https://www.hansonastronomy.com
Enjoy, Mark and Alex
[2] http://www.sai.msu.su/gcvs/cgi-bin/search2.cgi?search=V1025+Tau
[7] https://cdsarc.u-strasbg.fr/ftp/cats/B/gcvs/vartype.txt
[8] https://iopscience.iop.org/article/10.1088/0004-637X/698/1/242
[9] https://iopscience.iop.org/article/10.1088/0004-637X/698/1/242/pdf
[10] https://ui.adsabs.harvard.edu/abs/1994A%26A...287..145R/abstract
[11] https://ui.adsabs.harvard.edu/link_gateway/1994A%26A...287..145R/ADS_PDF
[12] https://iopscience.iop.org/article/10.3847/1538-4357/ab5aed
[13] https://iopscience.iop.org/article/10.3847/1538-4357/ab5aed/pdf
[14] https://iopscience.iop.org/article/10.1088/0004-637X/703/2/1511
[15] https://iopscience.iop.org/article/10.1088/0004-637X/703/2/1511/pdf
[16] https://www.aanda.org/articles/aa/full_html/2019/04/aa34337-18/aa34337-18.html
[17] https://www.aanda.org/articles/aa/pdf/2019/04/aa34337-18.pdf