TCP J18010186-2951258

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TCP J18010186-2951258

Postby Olivier GARDE » Sat Jul 14, 2018 9:16 am

New CBAT about this object :
http://www.cbat.eps.harvard.edu/unconf/ ... 51258.html

Christian and I made a spectrum of this target last night at the OHP during the annual spectro party and the spectra we got is visible here:
https://www.aavso.org/tcp-j18010186-295 ... agittarius

Very strange spectrum and at this date no confirmation about this kind of object.

Could be either a microlensing event and highly obscured supernova in milky Way (according to discussion in Facebook cataclysmic variables forum :
https://www.facebook.com/groups/7122470 ... st_mention
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Re: TCP J18010186-2951258

Postby Robin Leadbeater » Sat Jul 14, 2018 9:18 pm

Olivier GARDE wrote:New CBAT about this object :
highly obscured supernova in milky Way (according to discussion in Facebook cataclysmic variables forum :


Really ?? This would be extraordinary if it turns out to be true. Any neutrinos seen ? (Facebook is a place I avoid)
It is too low for me but definitely sounds like one to watch

Robin
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Re: TCP J18010186-2951258

Postby Francois Teyssier » Sun Jul 15, 2018 7:35 am

Lorenzo Franco also got a spectrum of the event

tcpj18010186-2951258_20180713_902_LFranco.png


ATel about the event:

ATEL #11853 ATEL #11853

Title: ASAS-SN Confirmation of a Bright and Possible High-Magnification
Microlensing Event
Author: Subo Dong (KIAA-PKU), K. Z. Stanek, C. S. Kochanek, T. Jayasinghe,
T. A. Thompson (OSU), J. L. Prieto (Diego Portales; MAS), B. J. Shappee
(Univ. of Hawaii), T. W.-S. Holoien (Carnegie)
Queries: dongsubo@pku.edu.cn
Posted: 14 Jul 2018; 16:51 UT
Subjects:Optical, Microlensing Event

The transient <a href=http://www.cbat.eps.harvard.edu/unconf/followups/J18010186-2951258.html>TCP
J18010186-2951258</a> was first discovered by T. Kojima on UT 2018 07
13.494. The <a href=https://asas-sn-s.asc.ohio-state.edu/light_curves/40857b7e-c8ad-4144-91a9-1ad5f12d66ee>ASAS-SN
Sky Patrol light curve </a> (Shappee et al. 2014; Kochanek et al. 2017)
suggested this to be a probable microlensing event. We take i-band follow-up
images with 40cm robotic telescopes of the Las Cumbres Observatory, and
the refined coordinates based on the follow-up observations are: (RA =
18:01:01.84 Dec=-29:51:23.8).

ASAS-SN has been regularly observing the field containing TCP J18010186-2951258
since 2016-03-10. The latest ASAS-SN photometry on UT 2018-07-14.1132905
shows that the source is at V = 10.73, and this is brighter than all previous
ASAS-SN measurements. The light curve is consistent with single-lens microlensing
models. Since we only have the rising part of the light curve, and due
to the degeneracy of blending, there are a number of single-lens microlensing
models compatible with data. One possible (though not unique) class of
microlensing models expect the event reaching high peak magnification on
around UT 2018 07 15 (<a href=http://www.astronomy.ohio-state.edu/~assassin/followup/TCPJ18010186-2951258.pdf>see
an example model here</a>). A high-magnification microlensing event is
sensitive to planets orbiting the lens star, and high-cadence photometric
follow ups are encouraged in the near future.

We thank Las Cumbres Observatory and its staff for their continued support
of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation
through grant GBMF5490 to the Ohio State University, NSF grant AST-1515927,
the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle
Physics (CCAPP) at OSU, and the Chinese Academy of Sciences South America
Center for Astronomy (CASSACA).
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Re: TCP J18010186-2951258

Postby Robin Leadbeater » Sun Jul 15, 2018 10:36 am

I spoke to Subo Dong last night and pointed him to the spectra. (I sometimes work with him and the ASASSN team on supernovae) Even if it turns out to be a microlensing event, the question still remains what type of star is this ? Subo does not think this is a CV. What does the spectrum look like with the Telluric and IS lines removed? Assuming it is a hot star with very high extinction, what objects have a narrow H alpha in absorption and no other obvious stellar features ?

Cheers
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Re: TCP J18010186-2951258

Postby Francois Teyssier » Thu Jul 26, 2018 10:34 am

Two new ATel


Is TCP J18010186-2951258 a binary lens?

ATel #11882; Nucita A. A., De Paolis F., Strafella F., & Licchelli D., Department of Mathematics & Physics, Unisalento
on 23 Jul 2018; 14:25 UT
Credential Certification: Achille Nucita (nucita@le.infn.it)


Subjects: Optical, Microlensing Event


Referred to by ATel #: 11883



The transient TCP J18010186-2951258 (at J2000 coordinates RA = 18:01:01.84 Dec=-29:51:23.8) was first discovered by T. Kojima on UT 2018 07 13.494 and the ASAS-SN Sky Patrol light curve (Shappee et al. 2014; Kochanek et al. 2017) resembles that of a microlensing event (Subo Dong et al. ATel #11853). By inspecting the ASAS-SN data around the peak we noticed an anomaly with respect to the Paczinsky best fit profile. Hence, including all currently (and free) archival V band data (AAVSO, and ASAS-SN) together with a few newly remotely acquired data using iTelescope.Net instruments (T17) n Siding Spring, Australia, (https://www.itelescope.net/) we find a best fit solution with a binary lens model with parameters q= 8.3E-3, b=0.66, t_0=113.8 (HJD-2458200), t_E= 19.5 days, u_0=0.027, theta = 2.63 radians, V_0 = 14.5. Subsequent analysis on the characteristics of the lens system parameters and the background source is in progress with the aim to test other possible models (including blending and finite source effects), check the robustness of the solution, confirm the binary lens model and, if so, refine the best fit parameters. Detailed analysis on the possible planetary feature will be presented elsewhere. This work makes use of ASAS-SN data (Shappee et al. 2014 and Kochanek et al. 2017). We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research. The use of the Siding Spring Observatory facilities is also acknowledged. We also remind that the BVRI band observations at the T17 Siding Spring iTelescope.Net instrument were performed in occasion of the "Sergio Fonti Summer School for Astronomy" held in Lecce (19-20, July, 2018), see http://www.dmf.unisalento.it/astro/Even ... _2018.html. We thank all the involved high school students and teachers for their enthusiastic participation in the observations and photometric analyses.

Possible binary lens fit http://www.dmf.unisalento.it/tagroup/download/LC.pdf


TCP J18010186-2951258 is likely not a binary microlensing event

ATel #11883; P. Mroz, A. Udalski (Warsaw University Observatory)
on 24 Jul 2018; 09:20 UT
Credential Certification: Przemek Mroz (pmroz@astrouw.edu.pl)


Subjects: Optical, Microlensing Event



Nucita et al. (ATel #11882) reported that the light curve of the microlensing event TCP J18010186-2951258 (ATel #11853) shows deviations from the single lens model that could be interpreted as a signature of the binary lens with the mass ratio q = 8.3e-3.

This event is located in the field BLG513 that is regularly monitored by the OGLE-IV Survey. The archival 22-year-long light curve of the source reveals semi-regular low-amplitude variability that is typical of OGLE small amplitude red giants. The strongest pulsation period is 155.4 d, but the light curve shows additional modulation on timescales of 10-20 d. Although the amplitude of variability in the baseline is small (0.03 mag or 3% of the flux in the I band), it is magnified by a factor ~30 during the microlensing event.

Deviations from the single lens model in the light curve of TCP J18010186-2951258 are likely caused by the variability of the source star, not by the binarity of the lens.





Assuming it is a hot star with very high extinction, what objects have a narrow H alpha in absorption and no other obvious stellar features ?

I wonder if lines are conserved through the deviation of the light by the lens object. I suppose it is not apochromactic :D

François
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Re: TCP J18010186-2951258

Postby Robin Leadbeater » Thu Jul 26, 2018 4:44 pm

Hi Francois,

I think the lensing effect itself is achromatic (all wavelengths deflected equally) but there are some reports of chromaticity in lensing, perhaps caused by different extinction in different paths or because emission at different wavelengths come from different locations in lensed extended sources. I think in general though the spectrum should survive the lensing. It did here for example.
http://www.threehillsobservatory.co.uk/ ... tra_30.htm

The Atel #11883 proposing that the deviations from the binary/extended source lensing model are due to pulsations of a red giant is strange. Pulsations might be a good explanation but surely the spectrum rules out this being a red giant (no molecular lines) ?

Robin
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Re: TCP J18010186-2951258

Postby Francois Teyssier » Thu Jul 26, 2018 4:48 pm

Thank you for the explanations and the link, Robin
François
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